Now that these are being included in 4.19, I am resending this 4.14 series. It was originally sent here:
https://lore.kernel.org/bpf/20210501043014.33300-5-fllinden@amazon.com/T/
v2: * The backport repairs in that original series were already included in 4.14, so they are no longer needed.
* Add additional commit for CVE-2021-31829.
* Added cherry-picks for CVE-2021-33200.
==
This series contains backports for BPF commits for 4.14, fixing some CVEs and making the verifier selftests clean (666 passed, 0 failures).
What the series does is:
* Fix selftests after recent bpf backports to 4.14 (but before the fixes for CVE-2021-29155). * Backport fixes for CVE-2021-29155, including selftests changes. * Backport commits that disallow the mangling of valid pointers by root (one commit that came in shortly after 4.14, one follow-up fix). This also means that 5 verifier selftests that always failed on the 4.14 branch are OK again. * Backport selftest commits to adapt alignment selftests after the previous. * Cherry-pick commit for CVE-2021-31829 * Cherry-pick commits for CVE-2021-33200
Verifier/alignment selftests are now clean on the 4.14 branch.
Listed by their mainline commit id, with comments on changes made for backporting:
0a13e3537ea6 ("bpf, selftests: Fix up some test_verifier cases for unprivileged") After some recent backports of bpf fixes to 4.14 (separate from this series), there are some selftests that need to be modified. This backported commit does that. No major conflicts/issues. For 4.14, some tests do not exist yet, so they were skipped.
The next ones are a backport of the BPF verifier fixes for CVE-2021-29155. Original series was part of the pull request here: https://lore.kernel.org/bpf/20210416223700.15611-1-daniel@iogearbox.net/T/
960114839252 ("bpf: Use correct permission flag for mixed signed bounds arithmetic") * Not applicable for 4.14, as it does not have 2c78ee898d8f ("bpf: Implement CAP_BPF").
6f55b2f2a117 ("bpf: Move off_reg into sanitize_ptr_alu") * Minor contextual conflict: verbose() does not have the env argument in 4.14.
24c109bb1537 ("bpf: Ensure off_reg has no mixed signed bounds for all types") * This deletes a switch() case in adjust_ptr_min_max_vals, since it moves the check in it to retrieve_ptr_limit. For 4.14, that switch() statement was still 2 if() statements, since it does not have aad2eeaf4697 ("bpf: Simplify ptr_min_max_vals adjustment").
The equivalent change for 4.14 is to delete the PTR_TO_MAP_VALUE if().
b658bbb844e2 ("bpf: Rework ptr_limit into alu_limit and add common error path") * Clean cherry-pick.
a6aaece00a57 ("bpf: Improve verifier error messages for users") * Simple contextual conflict in adjust_scalar_min_max_vals(). because of a var declaration that was added by this post-5.4 commit: 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking"). * Additional simple contextual conflict: verbose() does not have the env argument in 4.14.
073815b756c5 ("bpf: Refactor and streamline bounds check into helper") * This factors out the bounds check in adjust_ptr_min_max_vals in to a separate function. In 4.14, the bounds check block in question looks a little different, because: * 4.14 still uses allow_ptr_leaks, not bypass_spec_v1. * 01f810ace9ed ("bpf: Allow variable-offset stack access") changed the call to check_stack_access to a new function, check_stack_access_for_ptr_arithmetic(), and moved/changed an error message. * Since this commit just factors out some code from adjust_ptr_min_max_vals() in to a new function, do the same with the corresponding block in 4.14 that doesn't have the changes listed above from post-4.14 commits. f528819334 ("bpf: Move sanitize_val_alu out of op switch") * Resolved contextual conflict from post-4.14 commit 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking"), that added a comment on top of the switch referenced in the commit message.
7fedb63a8307 ("bpf: Tighten speculative pointer arithmetic mask") * Resolved contextual conflict post-4.14 commit: 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking") added a call to a new function just above the switch statement in adjust_ptr_min_max_vals. This doesn't affect the lines that were actually changed. * Resolved contextual conflict: 01f810ace9ed ("bpf: Allow variable-offset stack access") added a comment to the PTR_TO_STACK case in retrieve_ptr_limit. This comment is not present in 4.14, but the code is the same.
d7a509135175 ("bpf: Update selftests to reflect new error states") * Post-4.14, the verifier tests were split in to different files, in 4.14 they are still all in test_verifier.c. * The bounds.c tests have undergone several changes since 4.14, related to commits that were not backported (like e.g. the ALU32 changes). The error message will remain the same on 4.14. * 4f7b3e82589e ("bpf: improve verifier branch analysis") changed the error message for the "bounds checks mixing signed and unsigned, variant 14" test. Since 4.14 does not have that commit, this test will still produce the original error message ("R0 invalid mem access 'inv'").
These next commits are to pull in a few commits that get the number of verifier/align selftest errors on the 4.14 branch down to 0. This is mainly about the first one:
82abbf8d2fc4 ("bpf: do not allow root to mangle valid pointers") * This commit has a follow-up that must be added as well, see the next commit. * As the commit message states, this mostly disallows pointer mangling that was allowed by f1174f77b50c ("bpf/verifier: rework value tracking"). Allowing root to mangle valid pointers also results in the unexpected successful loading of some selftests, so backporting this fixes that. * Resolved contextual conflict: 4.14 does not have the env argument to verbose
dd066823db2a ("bpf/verifier: disallow pointer subtraction") * Fixes the above. * Minor contextual conflict: mark_reg_unknown does not have an env argument on 4.14.
2b36047e7889 ("selftests/bpf: fix test_align") * Selftest follow-up to 82abbf8d2fc4 ("bpf: do not allow root to mangle valid pointers") * Clean cherry-pick.
31e95b61e172 ("selftests/bpf: make 'dubious pointer arithmetic' test useful") * Selftest follow-up to the above. * Conflict: 4.14 does not have 'liveness' of registers in the output, so adjust the expected output to match.
The next commit is to fix CVE-2021-31829. One of two commits that fixes this was already applied (b9b34ddbe207 ("bpf: Fix masking negation logic upon negative dst register"), but we still need this one.
801c6058d14a ("bpf: Fix leakage of uninitialized bpf stack under speculation") * Minor fixup: e6ac593372aa ("bpf: Rename fixup_bpf_calls and add some comments") renamed fixup_bpf_calls, which did not happen on the 4.14 branch.
The last ones are for CVE-2021-33200, and were all clean cherry-picks. This also has a selftests change in mainline, but the test it changes isn't present in 4.14.
3d0220f6861d ("bpf: Wrap aux data inside bpf_sanitize_info container") bb01a1bba579 ("bpf: Fix mask direction swap upon off reg sign change") a7036191277f ("bpf: No need to simulate speculative domain for immediates")
====
Alexei Starovoitov (4): bpf: do not allow root to mangle valid pointers bpf/verifier: disallow pointer subtraction selftests/bpf: fix test_align selftests/bpf: make 'dubious pointer arithmetic' test useful
Daniel Borkmann (12): bpf: Move off_reg into sanitize_ptr_alu bpf: Ensure off_reg has no mixed signed bounds for all types bpf: Rework ptr_limit into alu_limit and add common error path bpf: Improve verifier error messages for users bpf: Refactor and streamline bounds check into helper bpf: Move sanitize_val_alu out of op switch bpf: Tighten speculative pointer arithmetic mask bpf: Update selftests to reflect new error states bpf: Fix leakage of uninitialized bpf stack under speculation bpf: Wrap aux data inside bpf_sanitize_info container bpf: Fix mask direction swap upon off reg sign change bpf: No need to simulate speculative domain for immediates
Piotr Krysiuk (1): bpf, selftests: Fix up some test_verifier cases for unprivileged
include/linux/bpf_verifier.h | 5 +- kernel/bpf/verifier.c | 369 ++++++++++++-------- tools/testing/selftests/bpf/test_align.c | 26 +- tools/testing/selftests/bpf/test_verifier.c | 114 +++--- 4 files changed, 299 insertions(+), 215 deletions(-)
From: Piotr Krysiuk piotras@gmail.com
commit 0a13e3537ea67452d549a6a80da3776d6b7dedb3 upstream.
Fix up test_verifier error messages for the case where the original error message changed, or for the case where pointer alu errors differ between privileged and unprivileged tests. Also, add alternative tests for keeping coverage of the original verifier rejection error message (fp alu), and newly reject map_ptr += rX where rX == 0 given we now forbid alu on these types for unprivileged. All test_verifier cases pass after the change. The test case fixups were kept separate to ease backporting of core changes.
Signed-off-by: Piotr Krysiuk piotras@gmail.com Co-developed-by: Daniel Borkmann daniel@iogearbox.net Signed-off-by: Daniel Borkmann daniel@iogearbox.net Acked-by: Alexei Starovoitov ast@kernel.org [fllinden@amazon.com: backport to 4.14, skipping non-existent tests] Signed-off-by: Frank van der Linden fllinden@amazon.com --- tools/testing/selftests/bpf/test_verifier.c | 44 ++++++++++++++++----- 1 file changed, 34 insertions(+), 10 deletions(-)
diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c index 9f7fc30d247d..43d91b2d2a21 100644 --- a/tools/testing/selftests/bpf/test_verifier.c +++ b/tools/testing/selftests/bpf/test_verifier.c @@ -2235,7 +2235,7 @@ static struct bpf_test tests[] = { .result = ACCEPT, }, { - "unpriv: adding of fp", + "unpriv: adding of fp, reg", .insns = { BPF_MOV64_IMM(BPF_REG_0, 0), BPF_MOV64_IMM(BPF_REG_1, 0), @@ -2243,9 +2243,22 @@ static struct bpf_test tests[] = { BPF_STX_MEM(BPF_DW, BPF_REG_1, BPF_REG_0, -8), BPF_EXIT_INSN(), }, - .result = ACCEPT, + .errstr_unpriv = "R1 tried to add from different maps, paths, or prohibited types", .result_unpriv = REJECT, + .result = ACCEPT, + }, + { + "unpriv: adding of fp, imm", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_MOV64_REG(BPF_REG_1, BPF_REG_10), + BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, 0), + BPF_STX_MEM(BPF_DW, BPF_REG_1, BPF_REG_0, -8), + BPF_EXIT_INSN(), + }, .errstr_unpriv = "R1 stack pointer arithmetic goes out of range", + .result_unpriv = REJECT, + .result = ACCEPT, }, { "unpriv: cmp of stack pointer", @@ -7766,8 +7779,9 @@ static struct bpf_test tests[] = { BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1), BPF_EXIT_INSN(), }, - .result = REJECT, + .errstr_unpriv = "R0 tried to sub from different maps, paths, or prohibited types", .errstr = "R0 tried to subtract pointer from scalar", + .result = REJECT, }, { "check deducing bounds from const, 2", @@ -7780,6 +7794,8 @@ static struct bpf_test tests[] = { BPF_ALU64_REG(BPF_SUB, BPF_REG_1, BPF_REG_0), BPF_EXIT_INSN(), }, + .errstr_unpriv = "R1 tried to sub from different maps, paths, or prohibited types", + .result_unpriv = REJECT, .result = ACCEPT, }, { @@ -7790,8 +7806,9 @@ static struct bpf_test tests[] = { BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1), BPF_EXIT_INSN(), }, - .result = REJECT, + .errstr_unpriv = "R0 tried to sub from different maps, paths, or prohibited types", .errstr = "R0 tried to subtract pointer from scalar", + .result = REJECT, }, { "check deducing bounds from const, 4", @@ -7804,6 +7821,8 @@ static struct bpf_test tests[] = { BPF_ALU64_REG(BPF_SUB, BPF_REG_1, BPF_REG_0), BPF_EXIT_INSN(), }, + .errstr_unpriv = "R1 tried to sub from different maps, paths, or prohibited types", + .result_unpriv = REJECT, .result = ACCEPT, }, { @@ -7814,8 +7833,9 @@ static struct bpf_test tests[] = { BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1), BPF_EXIT_INSN(), }, - .result = REJECT, + .errstr_unpriv = "R0 tried to sub from different maps, paths, or prohibited types", .errstr = "R0 tried to subtract pointer from scalar", + .result = REJECT, }, { "check deducing bounds from const, 6", @@ -7826,8 +7846,9 @@ static struct bpf_test tests[] = { BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1), BPF_EXIT_INSN(), }, - .result = REJECT, + .errstr_unpriv = "R0 tried to sub from different maps, paths, or prohibited types", .errstr = "R0 tried to subtract pointer from scalar", + .result = REJECT, }, { "check deducing bounds from const, 7", @@ -7839,8 +7860,9 @@ static struct bpf_test tests[] = { offsetof(struct __sk_buff, mark)), BPF_EXIT_INSN(), }, - .result = REJECT, + .errstr_unpriv = "R1 tried to sub from different maps, paths, or prohibited types", .errstr = "dereference of modified ctx ptr", + .result = REJECT, }, { "check deducing bounds from const, 8", @@ -7852,8 +7874,9 @@ static struct bpf_test tests[] = { offsetof(struct __sk_buff, mark)), BPF_EXIT_INSN(), }, - .result = REJECT, + .errstr_unpriv = "R1 tried to add from different maps, paths, or prohibited types", .errstr = "dereference of modified ctx ptr", + .result = REJECT, }, { "check deducing bounds from const, 9", @@ -7863,8 +7886,9 @@ static struct bpf_test tests[] = { BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1), BPF_EXIT_INSN(), }, - .result = REJECT, + .errstr_unpriv = "R0 tried to sub from different maps, paths, or prohibited types", .errstr = "R0 tried to subtract pointer from scalar", + .result = REJECT, }, { "check deducing bounds from const, 10", @@ -7876,8 +7900,8 @@ static struct bpf_test tests[] = { BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1), BPF_EXIT_INSN(), }, - .result = REJECT, .errstr = "math between ctx pointer and register with unbounded min value is not allowed", + .result = REJECT, }, { "XDP pkt read, pkt_end <= pkt_data', bad access 2",
From: Daniel Borkmann daniel@iogearbox.net
commit 6f55b2f2a1178856c19bbce2f71449926e731914 upstream.
Small refactor to drag off_reg into sanitize_ptr_alu(), so we later on can use off_reg for generalizing some of the checks for all pointer types.
Signed-off-by: Daniel Borkmann daniel@iogearbox.net Reviewed-by: John Fastabend john.fastabend@gmail.com Acked-by: Alexei Starovoitov ast@kernel.org [fllinden@amazon.com: fix minor contextual conflict for 4.14] Signed-off-by: Frank van der Linden fllinden@amazon.com --- kernel/bpf/verifier.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index f28ba90a43a7..434829d4438b 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2094,11 +2094,12 @@ static int sanitize_val_alu(struct bpf_verifier_env *env, static int sanitize_ptr_alu(struct bpf_verifier_env *env, struct bpf_insn *insn, const struct bpf_reg_state *ptr_reg, - struct bpf_reg_state *dst_reg, - bool off_is_neg) + const struct bpf_reg_state *off_reg, + struct bpf_reg_state *dst_reg) { struct bpf_verifier_state *vstate = env->cur_state; struct bpf_insn_aux_data *aux = cur_aux(env); + bool off_is_neg = off_reg->smin_value < 0; bool ptr_is_dst_reg = ptr_reg == dst_reg; u8 opcode = BPF_OP(insn->code); u32 alu_state, alu_limit; @@ -2224,7 +2225,7 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
switch (opcode) { case BPF_ADD: - ret = sanitize_ptr_alu(env, insn, ptr_reg, dst_reg, smin_val < 0); + ret = sanitize_ptr_alu(env, insn, ptr_reg, off_reg, dst_reg); if (ret < 0) { verbose("R%d tried to add from different maps, paths, or prohibited types\n", dst); return ret; @@ -2279,7 +2280,7 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, } break; case BPF_SUB: - ret = sanitize_ptr_alu(env, insn, ptr_reg, dst_reg, smin_val < 0); + ret = sanitize_ptr_alu(env, insn, ptr_reg, off_reg, dst_reg); if (ret < 0) { verbose("R%d tried to sub from different maps, paths, or prohibited types\n", dst); return ret;
From: Daniel Borkmann daniel@iogearbox.net
commit 24c109bb1537c12c02aeed2d51a347b4d6a9b76e upstream.
The mixed signed bounds check really belongs into retrieve_ptr_limit() instead of outside of it in adjust_ptr_min_max_vals(). The reason is that this check is not tied to PTR_TO_MAP_VALUE only, but to all pointer types that we handle in retrieve_ptr_limit() and given errors from the latter propagate back to adjust_ptr_min_max_vals() and lead to rejection of the program, it's a better place to reside to avoid anything slipping through for future types. The reason why we must reject such off_reg is that we otherwise would not be able to derive a mask, see details in 9d7eceede769 ("bpf: restrict unknown scalars of mixed signed bounds for unprivileged").
Signed-off-by: Daniel Borkmann daniel@iogearbox.net Reviewed-by: John Fastabend john.fastabend@gmail.com Acked-by: Alexei Starovoitov ast@kernel.org [fllinden@amazon.com: backport to 4.14] Signed-off-by: Frank van der Linden fllinden@amazon.com --- kernel/bpf/verifier.c | 19 +++++++++---------- 1 file changed, 9 insertions(+), 10 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 434829d4438b..9cb2c035f06d 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2025,12 +2025,18 @@ static struct bpf_insn_aux_data *cur_aux(struct bpf_verifier_env *env) }
static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg, - u32 *ptr_limit, u8 opcode, bool off_is_neg) + const struct bpf_reg_state *off_reg, + u32 *ptr_limit, u8 opcode) { + bool off_is_neg = off_reg->smin_value < 0; bool mask_to_left = (opcode == BPF_ADD && off_is_neg) || (opcode == BPF_SUB && !off_is_neg); u32 off, max;
+ if (!tnum_is_const(off_reg->var_off) && + (off_reg->smin_value < 0) != (off_reg->smax_value < 0)) + return -EACCES; + switch (ptr_reg->type) { case PTR_TO_STACK: /* Offset 0 is out-of-bounds, but acceptable start for the @@ -2121,7 +2127,7 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env, alu_state |= ptr_is_dst_reg ? BPF_ALU_SANITIZE_SRC : BPF_ALU_SANITIZE_DST;
- err = retrieve_ptr_limit(ptr_reg, &alu_limit, opcode, off_is_neg); + err = retrieve_ptr_limit(ptr_reg, off_reg, &alu_limit, opcode); if (err < 0) return err;
@@ -2164,8 +2170,8 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, smin_ptr = ptr_reg->smin_value, smax_ptr = ptr_reg->smax_value; u64 umin_val = off_reg->umin_value, umax_val = off_reg->umax_value, umin_ptr = ptr_reg->umin_value, umax_ptr = ptr_reg->umax_value; - u32 dst = insn->dst_reg, src = insn->src_reg; u8 opcode = BPF_OP(insn->code); + u32 dst = insn->dst_reg; int ret;
dst_reg = ®s[dst]; @@ -2205,13 +2211,6 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, dst); return -EACCES; } - if (ptr_reg->type == PTR_TO_MAP_VALUE) { - if (!env->allow_ptr_leaks && !known && (smin_val < 0) != (smax_val < 0)) { - verbose("R%d has unknown scalar with mixed signed bounds, pointer arithmetic with it prohibited for !root\n", - off_reg == dst_reg ? dst : src); - return -EACCES; - } - }
/* In case of 'scalar += pointer', dst_reg inherits pointer type and id. * The id may be overwritten later if we create a new variable offset.
From: Daniel Borkmann daniel@iogearbox.net
commit b658bbb844e28f1862867f37e8ca11a8e2aa94a3 upstream.
Small refactor with no semantic changes in order to consolidate the max ptr_limit boundary check.
Signed-off-by: Daniel Borkmann daniel@iogearbox.net Reviewed-by: John Fastabend john.fastabend@gmail.com Acked-by: Alexei Starovoitov ast@kernel.org --- kernel/bpf/verifier.c | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 9cb2c035f06d..12cb6b1c4e9b 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2026,12 +2026,12 @@ static struct bpf_insn_aux_data *cur_aux(struct bpf_verifier_env *env)
static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg, const struct bpf_reg_state *off_reg, - u32 *ptr_limit, u8 opcode) + u32 *alu_limit, u8 opcode) { bool off_is_neg = off_reg->smin_value < 0; bool mask_to_left = (opcode == BPF_ADD && off_is_neg) || (opcode == BPF_SUB && !off_is_neg); - u32 off, max; + u32 off, max = 0, ptr_limit = 0;
if (!tnum_is_const(off_reg->var_off) && (off_reg->smin_value < 0) != (off_reg->smax_value < 0)) @@ -2045,22 +2045,27 @@ static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg, max = MAX_BPF_STACK + mask_to_left; off = ptr_reg->off + ptr_reg->var_off.value; if (mask_to_left) - *ptr_limit = MAX_BPF_STACK + off; + ptr_limit = MAX_BPF_STACK + off; else - *ptr_limit = -off - 1; - return *ptr_limit >= max ? -ERANGE : 0; + ptr_limit = -off - 1; + break; case PTR_TO_MAP_VALUE: max = ptr_reg->map_ptr->value_size; if (mask_to_left) { - *ptr_limit = ptr_reg->umax_value + ptr_reg->off; + ptr_limit = ptr_reg->umax_value + ptr_reg->off; } else { off = ptr_reg->smin_value + ptr_reg->off; - *ptr_limit = ptr_reg->map_ptr->value_size - off - 1; + ptr_limit = ptr_reg->map_ptr->value_size - off - 1; } - return *ptr_limit >= max ? -ERANGE : 0; + break; default: return -EINVAL; } + + if (ptr_limit >= max) + return -ERANGE; + *alu_limit = ptr_limit; + return 0; }
static bool can_skip_alu_sanitation(const struct bpf_verifier_env *env,
From: Daniel Borkmann daniel@iogearbox.net
commit a6aaece00a57fa6f22575364b3903dfbccf5345d upstream.
Consolidate all error handling and provide more user-friendly error messages from sanitize_ptr_alu() and sanitize_val_alu().
Signed-off-by: Daniel Borkmann daniel@iogearbox.net Reviewed-by: John Fastabend john.fastabend@gmail.com Acked-by: Alexei Starovoitov ast@kernel.org [fllinden@amazon.com: backport to 4.14] Signed-off-by: Frank van der Linden fllinden@amazon.com --- kernel/bpf/verifier.c | 84 +++++++++++++++++++++++++++++++------------ 1 file changed, 62 insertions(+), 22 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 12cb6b1c4e9b..b44a4efeb1be 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2024,6 +2024,14 @@ static struct bpf_insn_aux_data *cur_aux(struct bpf_verifier_env *env) return &env->insn_aux_data[env->insn_idx]; }
+enum { + REASON_BOUNDS = -1, + REASON_TYPE = -2, + REASON_PATHS = -3, + REASON_LIMIT = -4, + REASON_STACK = -5, +}; + static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg, const struct bpf_reg_state *off_reg, u32 *alu_limit, u8 opcode) @@ -2035,7 +2043,7 @@ static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg,
if (!tnum_is_const(off_reg->var_off) && (off_reg->smin_value < 0) != (off_reg->smax_value < 0)) - return -EACCES; + return REASON_BOUNDS;
switch (ptr_reg->type) { case PTR_TO_STACK: @@ -2059,11 +2067,11 @@ static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg, } break; default: - return -EINVAL; + return REASON_TYPE; }
if (ptr_limit >= max) - return -ERANGE; + return REASON_LIMIT; *alu_limit = ptr_limit; return 0; } @@ -2083,7 +2091,7 @@ static int update_alu_sanitation_state(struct bpf_insn_aux_data *aux, if (aux->alu_state && (aux->alu_state != alu_state || aux->alu_limit != alu_limit)) - return -EACCES; + return REASON_PATHS;
/* Corresponding fixup done in fixup_bpf_calls(). */ aux->alu_state = alu_state; @@ -2156,7 +2164,46 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env, ret = push_stack(env, env->insn_idx + 1, env->insn_idx, true); if (!ptr_is_dst_reg && ret) *dst_reg = tmp; - return !ret ? -EFAULT : 0; + return !ret ? REASON_STACK : 0; +} + +static int sanitize_err(struct bpf_verifier_env *env, + const struct bpf_insn *insn, int reason, + const struct bpf_reg_state *off_reg, + const struct bpf_reg_state *dst_reg) +{ + static const char *err = "pointer arithmetic with it prohibited for !root"; + const char *op = BPF_OP(insn->code) == BPF_ADD ? "add" : "sub"; + u32 dst = insn->dst_reg, src = insn->src_reg; + + switch (reason) { + case REASON_BOUNDS: + verbose("R%d has unknown scalar with mixed signed bounds, %s\n", + off_reg == dst_reg ? dst : src, err); + break; + case REASON_TYPE: + verbose("R%d has pointer with unsupported alu operation, %s\n", + off_reg == dst_reg ? src : dst, err); + break; + case REASON_PATHS: + verbose("R%d tried to %s from different maps, paths or scalars, %s\n", + dst, op, err); + break; + case REASON_LIMIT: + verbose("R%d tried to %s beyond pointer bounds, %s\n", + dst, op, err); + break; + case REASON_STACK: + verbose("R%d could not be pushed for speculative verification, %s\n", + dst, err); + break; + default: + verbose("verifier internal error: unknown reason (%d)\n", + reason); + break; + } + + return -EACCES; }
/* Handles arithmetic on a pointer and a scalar: computes new min/max and var_off. @@ -2230,10 +2277,9 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, switch (opcode) { case BPF_ADD: ret = sanitize_ptr_alu(env, insn, ptr_reg, off_reg, dst_reg); - if (ret < 0) { - verbose("R%d tried to add from different maps, paths, or prohibited types\n", dst); - return ret; - } + if (ret < 0) + return sanitize_err(env, insn, ret, off_reg, dst_reg); + /* We can take a fixed offset as long as it doesn't overflow * the s32 'off' field */ @@ -2285,10 +2331,9 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, break; case BPF_SUB: ret = sanitize_ptr_alu(env, insn, ptr_reg, off_reg, dst_reg); - if (ret < 0) { - verbose("R%d tried to sub from different maps, paths, or prohibited types\n", dst); - return ret; - } + if (ret < 0) + return sanitize_err(env, insn, ret, off_reg, dst_reg); + if (dst_reg == off_reg) { /* scalar -= pointer. Creates an unknown scalar */ if (!env->allow_ptr_leaks) @@ -2412,7 +2457,6 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, s64 smin_val, smax_val; u64 umin_val, umax_val; u64 insn_bitness = (BPF_CLASS(insn->code) == BPF_ALU64) ? 64 : 32; - u32 dst = insn->dst_reg; int ret;
if (insn_bitness == 32) { @@ -2449,10 +2493,8 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, switch (opcode) { case BPF_ADD: ret = sanitize_val_alu(env, insn); - if (ret < 0) { - verbose("R%d tried to add from different pointers or scalars\n", dst); - return ret; - } + if (ret < 0) + return sanitize_err(env, insn, ret, NULL, NULL); if (signed_add_overflows(dst_reg->smin_value, smin_val) || signed_add_overflows(dst_reg->smax_value, smax_val)) { dst_reg->smin_value = S64_MIN; @@ -2473,10 +2515,8 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, break; case BPF_SUB: ret = sanitize_val_alu(env, insn); - if (ret < 0) { - verbose("R%d tried to sub from different pointers or scalars\n", dst); - return ret; - } + if (ret < 0) + return sanitize_err(env, insn, ret, NULL, NULL); if (signed_sub_overflows(dst_reg->smin_value, smax_val) || signed_sub_overflows(dst_reg->smax_value, smin_val)) { /* Overflow possible, we know nothing */
From: Daniel Borkmann daniel@iogearbox.net
commit 073815b756c51ba9d8384d924c5d1c03ca3d1ae4 upstream.
Move the bounds check in adjust_ptr_min_max_vals() into a small helper named sanitize_check_bounds() in order to simplify the former a bit.
Signed-off-by: Daniel Borkmann daniel@iogearbox.net Reviewed-by: John Fastabend john.fastabend@gmail.com Acked-by: Alexei Starovoitov ast@kernel.org [fllinden@amazon.com: backport to 4.14] Signed-off-by: Frank van der Linden fllinden@amazon.com --- kernel/bpf/verifier.c | 54 +++++++++++++++++++++++++++++-------------- 1 file changed, 37 insertions(+), 17 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index b44a4efeb1be..d178098f2298 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2206,6 +2206,41 @@ static int sanitize_err(struct bpf_verifier_env *env, return -EACCES; }
+static int sanitize_check_bounds(struct bpf_verifier_env *env, + const struct bpf_insn *insn, + const struct bpf_reg_state *dst_reg) +{ + u32 dst = insn->dst_reg; + + /* For unprivileged we require that resulting offset must be in bounds + * in order to be able to sanitize access later on. + */ + if (env->allow_ptr_leaks) + return 0; + + switch (dst_reg->type) { + case PTR_TO_STACK: + if (check_stack_access(env, dst_reg, dst_reg->off + + dst_reg->var_off.value, 1)) { + verbose("R%d stack pointer arithmetic goes out of range, " + "prohibited for !root\n", dst); + return -EACCES; + } + break; + case PTR_TO_MAP_VALUE: + if (check_map_access(env, dst, dst_reg->off, 1)) { + verbose("R%d pointer arithmetic of map value goes out of range, " + "prohibited for !root\n", dst); + return -EACCES; + } + break; + default: + break; + } + + return 0; +} + /* Handles arithmetic on a pointer and a scalar: computes new min/max and var_off. * Caller should also handle BPF_MOV case separately. * If we return -EACCES, caller may want to try again treating pointer as a @@ -2421,23 +2456,8 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, __reg_deduce_bounds(dst_reg); __reg_bound_offset(dst_reg);
- /* For unprivileged we require that resulting offset must be in bounds - * in order to be able to sanitize access later on. - */ - if (!env->allow_ptr_leaks) { - if (dst_reg->type == PTR_TO_MAP_VALUE && - check_map_access(env, dst, dst_reg->off, 1)) { - verbose("R%d pointer arithmetic of map value goes out of range, " - "prohibited for !root\n", dst); - return -EACCES; - } else if (dst_reg->type == PTR_TO_STACK && - check_stack_access(env, dst_reg, dst_reg->off + - dst_reg->var_off.value, 1)) { - verbose("R%d stack pointer arithmetic goes out of range, " - "prohibited for !root\n", dst); - return -EACCES; - } - } + if (sanitize_check_bounds(env, insn, dst_reg) < 0) + return -EACCES;
return 0; }
From: Daniel Borkmann daniel@iogearbox.net
commit f528819334881fd622fdadeddb3f7edaed8b7c9b upstream.
Add a small sanitize_needed() helper function and move sanitize_val_alu() out of the main opcode switch. In upcoming work, we'll move sanitize_ptr_alu() as well out of its opcode switch so this helps to streamline both.
Signed-off-by: Daniel Borkmann daniel@iogearbox.net Reviewed-by: John Fastabend john.fastabend@gmail.com Acked-by: Alexei Starovoitov ast@kernel.org [fllinden@amazon.com: backported to 4.14] Signed-off-by: Frank van der Linden fllinden@amazon.com --- kernel/bpf/verifier.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index d178098f2298..f76177a37b18 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2110,6 +2110,11 @@ static int sanitize_val_alu(struct bpf_verifier_env *env, return update_alu_sanitation_state(aux, BPF_ALU_NON_POINTER, 0); }
+static bool sanitize_needed(u8 opcode) +{ + return opcode == BPF_ADD || opcode == BPF_SUB; +} + static int sanitize_ptr_alu(struct bpf_verifier_env *env, struct bpf_insn *insn, const struct bpf_reg_state *ptr_reg, @@ -2510,11 +2515,14 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, return 0; }
- switch (opcode) { - case BPF_ADD: + if (sanitize_needed(opcode)) { ret = sanitize_val_alu(env, insn); if (ret < 0) return sanitize_err(env, insn, ret, NULL, NULL); + } + + switch (opcode) { + case BPF_ADD: if (signed_add_overflows(dst_reg->smin_value, smin_val) || signed_add_overflows(dst_reg->smax_value, smax_val)) { dst_reg->smin_value = S64_MIN; @@ -2534,9 +2542,6 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, dst_reg->var_off = tnum_add(dst_reg->var_off, src_reg.var_off); break; case BPF_SUB: - ret = sanitize_val_alu(env, insn); - if (ret < 0) - return sanitize_err(env, insn, ret, NULL, NULL); if (signed_sub_overflows(dst_reg->smin_value, smax_val) || signed_sub_overflows(dst_reg->smax_value, smin_val)) { /* Overflow possible, we know nothing */
From: Daniel Borkmann daniel@iogearbox.net
commit 7fedb63a8307dda0ec3b8969a3b233a1dd7ea8e0 upstream.
This work tightens the offset mask we use for unprivileged pointer arithmetic in order to mitigate a corner case reported by Piotr and Benedict where in the speculative domain it is possible to advance, for example, the map value pointer by up to value_size-1 out-of-bounds in order to leak kernel memory via side-channel to user space.
Before this change, the computed ptr_limit for retrieve_ptr_limit() helper represents largest valid distance when moving pointer to the right or left which is then fed as aux->alu_limit to generate masking instructions against the offset register. After the change, the derived aux->alu_limit represents the largest potential value of the offset register which we mask against which is just a narrower subset of the former limit.
For minimal complexity, we call sanitize_ptr_alu() from 2 observation points in adjust_ptr_min_max_vals(), that is, before and after the simulated alu operation. In the first step, we retieve the alu_state and alu_limit before the operation as well as we branch-off a verifier path and push it to the verification stack as we did before which checks the dst_reg under truncation, in other words, when the speculative domain would attempt to move the pointer out-of-bounds.
In the second step, we retrieve the new alu_limit and calculate the absolute distance between both. Moreover, we commit the alu_state and final alu_limit via update_alu_sanitation_state() to the env's instruction aux data, and bail out from there if there is a mismatch due to coming from different verification paths with different states.
Reported-by: Piotr Krysiuk piotras@gmail.com Reported-by: Benedict Schlueter benedict.schlueter@rub.de Signed-off-by: Daniel Borkmann daniel@iogearbox.net Reviewed-by: John Fastabend john.fastabend@gmail.com Acked-by: Alexei Starovoitov ast@kernel.org Tested-by: Benedict Schlueter benedict.schlueter@rub.de [fllinden@amazon.com: backported to 4.14] Signed-off-by: Frank van der Linden fllinden@amazon.com --- kernel/bpf/verifier.c | 70 +++++++++++++++++++++++++++---------------- 1 file changed, 44 insertions(+), 26 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index f76177a37b18..1a39a89e1584 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2039,7 +2039,7 @@ static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg, bool off_is_neg = off_reg->smin_value < 0; bool mask_to_left = (opcode == BPF_ADD && off_is_neg) || (opcode == BPF_SUB && !off_is_neg); - u32 off, max = 0, ptr_limit = 0; + u32 max = 0, ptr_limit = 0;
if (!tnum_is_const(off_reg->var_off) && (off_reg->smin_value < 0) != (off_reg->smax_value < 0)) @@ -2048,23 +2048,18 @@ static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg, switch (ptr_reg->type) { case PTR_TO_STACK: /* Offset 0 is out-of-bounds, but acceptable start for the - * left direction, see BPF_REG_FP. + * left direction, see BPF_REG_FP. Also, unknown scalar + * offset where we would need to deal with min/max bounds is + * currently prohibited for unprivileged. */ max = MAX_BPF_STACK + mask_to_left; - off = ptr_reg->off + ptr_reg->var_off.value; - if (mask_to_left) - ptr_limit = MAX_BPF_STACK + off; - else - ptr_limit = -off - 1; + ptr_limit = -(ptr_reg->var_off.value + ptr_reg->off); break; case PTR_TO_MAP_VALUE: max = ptr_reg->map_ptr->value_size; - if (mask_to_left) { - ptr_limit = ptr_reg->umax_value + ptr_reg->off; - } else { - off = ptr_reg->smin_value + ptr_reg->off; - ptr_limit = ptr_reg->map_ptr->value_size - off - 1; - } + ptr_limit = (mask_to_left ? + ptr_reg->smin_value : + ptr_reg->umax_value) + ptr_reg->off; break; default: return REASON_TYPE; @@ -2119,10 +2114,12 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env, struct bpf_insn *insn, const struct bpf_reg_state *ptr_reg, const struct bpf_reg_state *off_reg, - struct bpf_reg_state *dst_reg) + struct bpf_reg_state *dst_reg, + struct bpf_insn_aux_data *tmp_aux, + const bool commit_window) { + struct bpf_insn_aux_data *aux = commit_window ? cur_aux(env) : tmp_aux; struct bpf_verifier_state *vstate = env->cur_state; - struct bpf_insn_aux_data *aux = cur_aux(env); bool off_is_neg = off_reg->smin_value < 0; bool ptr_is_dst_reg = ptr_reg == dst_reg; u8 opcode = BPF_OP(insn->code); @@ -2141,18 +2138,33 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env, if (vstate->speculative) goto do_sim;
- alu_state = off_is_neg ? BPF_ALU_NEG_VALUE : 0; - alu_state |= ptr_is_dst_reg ? - BPF_ALU_SANITIZE_SRC : BPF_ALU_SANITIZE_DST; - err = retrieve_ptr_limit(ptr_reg, off_reg, &alu_limit, opcode); if (err < 0) return err;
+ if (commit_window) { + /* In commit phase we narrow the masking window based on + * the observed pointer move after the simulated operation. + */ + alu_state = tmp_aux->alu_state; + alu_limit = abs(tmp_aux->alu_limit - alu_limit); + } else { + alu_state = off_is_neg ? BPF_ALU_NEG_VALUE : 0; + alu_state |= ptr_is_dst_reg ? + BPF_ALU_SANITIZE_SRC : BPF_ALU_SANITIZE_DST; + } + err = update_alu_sanitation_state(aux, alu_state, alu_limit); if (err < 0) return err; do_sim: + /* If we're in commit phase, we're done here given we already + * pushed the truncated dst_reg into the speculative verification + * stack. + */ + if (commit_window) + return 0; + /* Simulate and find potential out-of-bounds access under * speculative execution from truncation as a result of * masking when off was not within expected range. If off @@ -2262,6 +2274,7 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, smin_ptr = ptr_reg->smin_value, smax_ptr = ptr_reg->smax_value; u64 umin_val = off_reg->umin_value, umax_val = off_reg->umax_value, umin_ptr = ptr_reg->umin_value, umax_ptr = ptr_reg->umax_value; + struct bpf_insn_aux_data tmp_aux = {}; u8 opcode = BPF_OP(insn->code); u32 dst = insn->dst_reg; int ret; @@ -2314,12 +2327,15 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, !check_reg_sane_offset(env, ptr_reg, ptr_reg->type)) return -EINVAL;
- switch (opcode) { - case BPF_ADD: - ret = sanitize_ptr_alu(env, insn, ptr_reg, off_reg, dst_reg); + if (sanitize_needed(opcode)) { + ret = sanitize_ptr_alu(env, insn, ptr_reg, off_reg, dst_reg, + &tmp_aux, false); if (ret < 0) return sanitize_err(env, insn, ret, off_reg, dst_reg); + }
+ switch (opcode) { + case BPF_ADD: /* We can take a fixed offset as long as it doesn't overflow * the s32 'off' field */ @@ -2370,10 +2386,6 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, } break; case BPF_SUB: - ret = sanitize_ptr_alu(env, insn, ptr_reg, off_reg, dst_reg); - if (ret < 0) - return sanitize_err(env, insn, ret, off_reg, dst_reg); - if (dst_reg == off_reg) { /* scalar -= pointer. Creates an unknown scalar */ if (!env->allow_ptr_leaks) @@ -2463,6 +2475,12 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
if (sanitize_check_bounds(env, insn, dst_reg) < 0) return -EACCES; + if (sanitize_needed(opcode)) { + ret = sanitize_ptr_alu(env, insn, dst_reg, off_reg, dst_reg, + &tmp_aux, true); + if (ret < 0) + return sanitize_err(env, insn, ret, off_reg, dst_reg); + }
return 0; }
From: Daniel Borkmann daniel@iogearbox.net
commit d7a5091351756d0ae8e63134313c455624e36a13 upstream.
Update various selftest error messages:
* The 'Rx tried to sub from different maps, paths, or prohibited types' is reworked into more specific/differentiated error messages for better guidance.
* The change into 'value -4294967168 makes map_value pointer be out of bounds' is due to moving the mixed bounds check into the speculation handling and thus occuring slightly later than above mentioned sanity check.
* The change into 'math between map_value pointer and register with unbounded min value' is similarly due to register sanity check coming before the mixed bounds check.
* The case of 'map access: known scalar += value_ptr from different maps' now loads fine given masks are the same from the different paths (despite max map value size being different).
Signed-off-by: Daniel Borkmann daniel@iogearbox.net Reviewed-by: John Fastabend john.fastabend@gmail.com Acked-by: Alexei Starovoitov ast@kernel.org [fllinden@amazon.com - 4.14 backport, account for split test_verifier and different / missing tests] Signed-off-by: Frank van der Linden fllinden@amazon.com --- tools/testing/selftests/bpf/test_verifier.c | 34 ++++++++------------- 1 file changed, 12 insertions(+), 22 deletions(-)
diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c index 43d91b2d2a21..bab9942b20b2 100644 --- a/tools/testing/selftests/bpf/test_verifier.c +++ b/tools/testing/selftests/bpf/test_verifier.c @@ -2243,7 +2243,7 @@ static struct bpf_test tests[] = { BPF_STX_MEM(BPF_DW, BPF_REG_1, BPF_REG_0, -8), BPF_EXIT_INSN(), }, - .errstr_unpriv = "R1 tried to add from different maps, paths, or prohibited types", + .errstr_unpriv = "R1 stack pointer arithmetic goes out of range", .result_unpriv = REJECT, .result = ACCEPT, }, @@ -6220,7 +6220,6 @@ static struct bpf_test tests[] = { }, .fixup_map1 = { 3 }, .errstr = "unbounded min value", - .errstr_unpriv = "R1 has unknown scalar with mixed signed bounds", .result = REJECT, }, { @@ -6245,7 +6244,6 @@ static struct bpf_test tests[] = { }, .fixup_map1 = { 3 }, .errstr = "unbounded min value", - .errstr_unpriv = "R1 has unknown scalar with mixed signed bounds", .result = REJECT, }, { @@ -6272,7 +6270,6 @@ static struct bpf_test tests[] = { }, .fixup_map1 = { 3 }, .errstr = "unbounded min value", - .errstr_unpriv = "R8 has unknown scalar with mixed signed bounds", .result = REJECT, }, { @@ -6298,7 +6295,6 @@ static struct bpf_test tests[] = { }, .fixup_map1 = { 3 }, .errstr = "unbounded min value", - .errstr_unpriv = "R8 has unknown scalar with mixed signed bounds", .result = REJECT, }, { @@ -6347,7 +6343,6 @@ static struct bpf_test tests[] = { }, .fixup_map1 = { 3 }, .errstr = "unbounded min value", - .errstr_unpriv = "R1 has unknown scalar with mixed signed bounds", .result = REJECT, }, { @@ -6419,7 +6414,6 @@ static struct bpf_test tests[] = { }, .fixup_map1 = { 3 }, .errstr = "unbounded min value", - .errstr_unpriv = "R1 has unknown scalar with mixed signed bounds", .result = REJECT, }, { @@ -6471,7 +6465,6 @@ static struct bpf_test tests[] = { }, .fixup_map1 = { 3 }, .errstr = "unbounded min value", - .errstr_unpriv = "R1 has unknown scalar with mixed signed bounds", .result = REJECT, }, { @@ -6499,7 +6492,6 @@ static struct bpf_test tests[] = { }, .fixup_map1 = { 3 }, .errstr = "unbounded min value", - .errstr_unpriv = "R1 has unknown scalar with mixed signed bounds", .result = REJECT, }, { @@ -6526,7 +6518,6 @@ static struct bpf_test tests[] = { }, .fixup_map1 = { 3 }, .errstr = "unbounded min value", - .errstr_unpriv = "R1 has unknown scalar with mixed signed bounds", .result = REJECT, }, { @@ -6556,7 +6547,6 @@ static struct bpf_test tests[] = { }, .fixup_map1 = { 3 }, .errstr = "unbounded min value", - .errstr_unpriv = "R7 has unknown scalar with mixed signed bounds", .result = REJECT, }, { @@ -6615,7 +6605,6 @@ static struct bpf_test tests[] = { }, .fixup_map1 = { 3 }, .errstr = "unbounded min value", - .errstr_unpriv = "R1 has unknown scalar with mixed signed bounds", .result = REJECT, .result_unpriv = REJECT, }, @@ -7779,7 +7768,7 @@ static struct bpf_test tests[] = { BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1), BPF_EXIT_INSN(), }, - .errstr_unpriv = "R0 tried to sub from different maps, paths, or prohibited types", + .errstr_unpriv = "R1 has pointer with unsupported alu operation", .errstr = "R0 tried to subtract pointer from scalar", .result = REJECT, }, @@ -7794,7 +7783,7 @@ static struct bpf_test tests[] = { BPF_ALU64_REG(BPF_SUB, BPF_REG_1, BPF_REG_0), BPF_EXIT_INSN(), }, - .errstr_unpriv = "R1 tried to sub from different maps, paths, or prohibited types", + .errstr_unpriv = "R1 has pointer with unsupported alu operation", .result_unpriv = REJECT, .result = ACCEPT, }, @@ -7806,22 +7795,23 @@ static struct bpf_test tests[] = { BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1), BPF_EXIT_INSN(), }, - .errstr_unpriv = "R0 tried to sub from different maps, paths, or prohibited types", + .errstr_unpriv = "R1 has pointer with unsupported alu operation", .errstr = "R0 tried to subtract pointer from scalar", .result = REJECT, }, { "check deducing bounds from const, 4", .insns = { + BPF_MOV64_REG(BPF_REG_6, BPF_REG_1), BPF_MOV64_IMM(BPF_REG_0, 0), BPF_JMP_IMM(BPF_JSLE, BPF_REG_0, 0, 1), BPF_EXIT_INSN(), BPF_JMP_IMM(BPF_JSGE, BPF_REG_0, 0, 1), BPF_EXIT_INSN(), - BPF_ALU64_REG(BPF_SUB, BPF_REG_1, BPF_REG_0), + BPF_ALU64_REG(BPF_SUB, BPF_REG_6, BPF_REG_0), BPF_EXIT_INSN(), }, - .errstr_unpriv = "R1 tried to sub from different maps, paths, or prohibited types", + .errstr_unpriv = "R6 has pointer with unsupported alu operation", .result_unpriv = REJECT, .result = ACCEPT, }, @@ -7833,7 +7823,7 @@ static struct bpf_test tests[] = { BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1), BPF_EXIT_INSN(), }, - .errstr_unpriv = "R0 tried to sub from different maps, paths, or prohibited types", + .errstr_unpriv = "R1 has pointer with unsupported alu operation", .errstr = "R0 tried to subtract pointer from scalar", .result = REJECT, }, @@ -7846,7 +7836,7 @@ static struct bpf_test tests[] = { BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1), BPF_EXIT_INSN(), }, - .errstr_unpriv = "R0 tried to sub from different maps, paths, or prohibited types", + .errstr_unpriv = "R1 has pointer with unsupported alu operation", .errstr = "R0 tried to subtract pointer from scalar", .result = REJECT, }, @@ -7860,7 +7850,7 @@ static struct bpf_test tests[] = { offsetof(struct __sk_buff, mark)), BPF_EXIT_INSN(), }, - .errstr_unpriv = "R1 tried to sub from different maps, paths, or prohibited types", + .errstr_unpriv = "R1 has pointer with unsupported alu operation", .errstr = "dereference of modified ctx ptr", .result = REJECT, }, @@ -7874,7 +7864,7 @@ static struct bpf_test tests[] = { offsetof(struct __sk_buff, mark)), BPF_EXIT_INSN(), }, - .errstr_unpriv = "R1 tried to add from different maps, paths, or prohibited types", + .errstr_unpriv = "R1 has pointer with unsupported alu operation", .errstr = "dereference of modified ctx ptr", .result = REJECT, }, @@ -7886,7 +7876,7 @@ static struct bpf_test tests[] = { BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1), BPF_EXIT_INSN(), }, - .errstr_unpriv = "R0 tried to sub from different maps, paths, or prohibited types", + .errstr_unpriv = "R1 has pointer with unsupported alu operation", .errstr = "R0 tried to subtract pointer from scalar", .result = REJECT, },
From: Alexei Starovoitov ast@kernel.org
commit 82abbf8d2fc46d79611ab58daa7c608df14bb3ee upstream.
Do not allow root to convert valid pointers into unknown scalars. In particular disallow: ptr &= reg ptr <<= reg ptr += ptr and explicitly allow: ptr -= ptr since pkt_end - pkt == length
1. This minimizes amount of address leaks root can do. In the future may need to further tighten the leaks with kptr_restrict.
2. If program has such pointer math it's likely a user mistake and when verifier complains about it right away instead of many instructions later on invalid memory access it's easier for users to fix their progs.
3. when register holding a pointer cannot change to scalar it allows JITs to optimize better. Like 32-bit archs could use single register for pointers instead of a pair required to hold 64-bit scalars.
4. reduces architecture dependent behavior. Since code: r1 = r10; r1 &= 0xff; if (r1 ...) will behave differently arm64 vs x64 and offloaded vs native.
A significant chunk of ptr mangling was allowed by commit f1174f77b50c ("bpf/verifier: rework value tracking") yet some of it was allowed even earlier.
Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net [fllinden@amazon.com: backport to 4.14] Signed-off-by: Frank van der Linden fllinden@amazon.com --- kernel/bpf/verifier.c | 100 +++++++------------- tools/testing/selftests/bpf/test_verifier.c | 56 +++++------ 2 files changed, 62 insertions(+), 94 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 1a39a89e1584..b999e268ee23 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2292,28 +2292,24 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
if (BPF_CLASS(insn->code) != BPF_ALU64) { /* 32-bit ALU ops on pointers produce (meaningless) scalars */ - if (!env->allow_ptr_leaks) - verbose("R%d 32-bit pointer arithmetic prohibited\n", - dst); + verbose("R%d 32-bit pointer arithmetic prohibited\n", + dst); return -EACCES; }
if (ptr_reg->type == PTR_TO_MAP_VALUE_OR_NULL) { - if (!env->allow_ptr_leaks) - verbose("R%d pointer arithmetic on PTR_TO_MAP_VALUE_OR_NULL prohibited, null-check it first\n", - dst); + verbose("R%d pointer arithmetic on PTR_TO_MAP_VALUE_OR_NULL prohibited, null-check it first\n", + dst); return -EACCES; } if (ptr_reg->type == CONST_PTR_TO_MAP) { - if (!env->allow_ptr_leaks) - verbose("R%d pointer arithmetic on CONST_PTR_TO_MAP prohibited\n", - dst); + verbose("R%d pointer arithmetic on CONST_PTR_TO_MAP prohibited\n", + dst); return -EACCES; } if (ptr_reg->type == PTR_TO_PACKET_END) { - if (!env->allow_ptr_leaks) - verbose("R%d pointer arithmetic on PTR_TO_PACKET_END prohibited\n", - dst); + verbose("R%d pointer arithmetic on PTR_TO_PACKET_END prohibited\n", + dst); return -EACCES; }
@@ -2388,9 +2384,8 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, case BPF_SUB: if (dst_reg == off_reg) { /* scalar -= pointer. Creates an unknown scalar */ - if (!env->allow_ptr_leaks) - verbose("R%d tried to subtract pointer from scalar\n", - dst); + verbose("R%d tried to subtract pointer from scalar\n", + dst); return -EACCES; } /* We don't allow subtraction from FP, because (according to @@ -2398,9 +2393,8 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, * be able to deal with it. */ if (ptr_reg->type == PTR_TO_STACK) { - if (!env->allow_ptr_leaks) - verbose("R%d subtraction from stack pointer prohibited\n", - dst); + verbose("R%d subtraction from stack pointer prohibited\n", + dst); return -EACCES; } if (known && (ptr_reg->off - smin_val == @@ -2450,19 +2444,14 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, case BPF_AND: case BPF_OR: case BPF_XOR: - /* bitwise ops on pointers are troublesome, prohibit for now. - * (However, in principle we could allow some cases, e.g. - * ptr &= ~3 which would reduce min_value by 3.) - */ - if (!env->allow_ptr_leaks) - verbose("R%d bitwise operator %s on pointer prohibited\n", - dst, bpf_alu_string[opcode >> 4]); + /* bitwise ops on pointers are troublesome. */ + verbose("R%d bitwise operator %s on pointer prohibited\n", + dst, bpf_alu_string[opcode >> 4]); return -EACCES; default: /* other operators (e.g. MUL,LSH) produce non-pointer results */ - if (!env->allow_ptr_leaks) - verbose("R%d pointer arithmetic with %s operator prohibited\n", - dst, bpf_alu_string[opcode >> 4]); + verbose("R%d pointer arithmetic with %s operator prohibited\n", + dst, bpf_alu_string[opcode >> 4]); return -EACCES; }
@@ -2752,7 +2741,6 @@ static int adjust_reg_min_max_vals(struct bpf_verifier_env *env, struct bpf_reg_state *regs = cur_regs(env), *dst_reg, *src_reg; struct bpf_reg_state *ptr_reg = NULL, off_reg = {0}; u8 opcode = BPF_OP(insn->code); - int rc;
dst_reg = ®s[insn->dst_reg]; src_reg = NULL; @@ -2763,43 +2751,29 @@ static int adjust_reg_min_max_vals(struct bpf_verifier_env *env, if (src_reg->type != SCALAR_VALUE) { if (dst_reg->type != SCALAR_VALUE) { /* Combining two pointers by any ALU op yields - * an arbitrary scalar. + * an arbitrary scalar. Disallow all math except + * pointer subtraction */ - if (!env->allow_ptr_leaks) { - verbose("R%d pointer %s pointer prohibited\n", - insn->dst_reg, - bpf_alu_string[opcode >> 4]); - return -EACCES; + if (opcode == BPF_SUB){ + mark_reg_unknown(regs, insn->dst_reg); + return 0; } - mark_reg_unknown(regs, insn->dst_reg); - return 0; + verbose("R%d pointer %s pointer prohibited\n", + insn->dst_reg, + bpf_alu_string[opcode >> 4]); + return -EACCES; } else { /* scalar += pointer * This is legal, but we have to reverse our * src/dest handling in computing the range */ - rc = adjust_ptr_min_max_vals(env, insn, - src_reg, dst_reg); - if (rc == -EACCES && env->allow_ptr_leaks) { - /* scalar += unknown scalar */ - __mark_reg_unknown(&off_reg); - return adjust_scalar_min_max_vals( - env, insn, - dst_reg, off_reg); - } - return rc; + return adjust_ptr_min_max_vals(env, insn, + src_reg, dst_reg); } } else if (ptr_reg) { /* pointer += scalar */ - rc = adjust_ptr_min_max_vals(env, insn, - dst_reg, src_reg); - if (rc == -EACCES && env->allow_ptr_leaks) { - /* unknown scalar += scalar */ - __mark_reg_unknown(dst_reg); - return adjust_scalar_min_max_vals( - env, insn, dst_reg, *src_reg); - } - return rc; + return adjust_ptr_min_max_vals(env, insn, + dst_reg, src_reg); } } else { /* Pretend the src is a reg with a known value, since we only @@ -2808,17 +2782,9 @@ static int adjust_reg_min_max_vals(struct bpf_verifier_env *env, off_reg.type = SCALAR_VALUE; __mark_reg_known(&off_reg, insn->imm); src_reg = &off_reg; - if (ptr_reg) { /* pointer += K */ - rc = adjust_ptr_min_max_vals(env, insn, - ptr_reg, src_reg); - if (rc == -EACCES && env->allow_ptr_leaks) { - /* unknown scalar += K */ - __mark_reg_unknown(dst_reg); - return adjust_scalar_min_max_vals( - env, insn, dst_reg, off_reg); - } - return rc; - } + if (ptr_reg) /* pointer += K */ + return adjust_ptr_min_max_vals(env, insn, + ptr_reg, src_reg); }
/* Got here implies adding two SCALAR_VALUEs */ diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c index bab9942b20b2..d4f611546fc0 100644 --- a/tools/testing/selftests/bpf/test_verifier.c +++ b/tools/testing/selftests/bpf/test_verifier.c @@ -462,9 +462,7 @@ static struct bpf_test tests[] = { BPF_STX_MEM(BPF_DW, BPF_REG_1, BPF_REG_0, 0), BPF_EXIT_INSN(), }, - .errstr_unpriv = "R1 subtraction from stack pointer", - .result_unpriv = REJECT, - .errstr = "R1 invalid mem access", + .errstr = "R1 subtraction from stack pointer", .result = REJECT, }, { @@ -1900,9 +1898,8 @@ static struct bpf_test tests[] = { BPF_MOV64_IMM(BPF_REG_0, 0), BPF_EXIT_INSN(), }, - .result = ACCEPT, - .result_unpriv = REJECT, - .errstr_unpriv = "R1 pointer += pointer", + .result = REJECT, + .errstr = "R1 pointer += pointer", }, { "unpriv: neg pointer", @@ -2694,7 +2691,8 @@ static struct bpf_test tests[] = { BPF_LDX_MEM(BPF_W, BPF_REG_3, BPF_REG_1, offsetof(struct __sk_buff, data)), BPF_ALU64_REG(BPF_ADD, BPF_REG_3, BPF_REG_4), - BPF_MOV64_REG(BPF_REG_2, BPF_REG_1), + BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1, + offsetof(struct __sk_buff, len)), BPF_ALU64_IMM(BPF_LSH, BPF_REG_2, 49), BPF_ALU64_IMM(BPF_RSH, BPF_REG_2, 49), BPF_ALU64_REG(BPF_ADD, BPF_REG_3, BPF_REG_2), @@ -3001,7 +2999,7 @@ static struct bpf_test tests[] = { BPF_MOV64_IMM(BPF_REG_0, 0), BPF_EXIT_INSN(), }, - .errstr = "invalid access to packet", + .errstr = "R3 pointer arithmetic on PTR_TO_PACKET_END", .result = REJECT, .prog_type = BPF_PROG_TYPE_SCHED_CLS, }, @@ -3988,9 +3986,7 @@ static struct bpf_test tests[] = { BPF_EXIT_INSN(), }, .fixup_map2 = { 3, 11 }, - .errstr_unpriv = "R0 pointer += pointer", - .errstr = "R0 invalid mem access 'inv'", - .result_unpriv = REJECT, + .errstr = "R0 pointer += pointer", .result = REJECT, .flags = F_NEEDS_EFFICIENT_UNALIGNED_ACCESS, }, @@ -4031,7 +4027,7 @@ static struct bpf_test tests[] = { BPF_EXIT_INSN(), }, .fixup_map1 = { 4 }, - .errstr = "R4 invalid mem access", + .errstr = "R4 pointer arithmetic on PTR_TO_MAP_VALUE_OR_NULL", .result = REJECT, .prog_type = BPF_PROG_TYPE_SCHED_CLS }, @@ -4052,7 +4048,7 @@ static struct bpf_test tests[] = { BPF_EXIT_INSN(), }, .fixup_map1 = { 4 }, - .errstr = "R4 invalid mem access", + .errstr = "R4 pointer arithmetic on PTR_TO_MAP_VALUE_OR_NULL", .result = REJECT, .prog_type = BPF_PROG_TYPE_SCHED_CLS }, @@ -4073,7 +4069,7 @@ static struct bpf_test tests[] = { BPF_EXIT_INSN(), }, .fixup_map1 = { 4 }, - .errstr = "R4 invalid mem access", + .errstr = "R4 pointer arithmetic on PTR_TO_MAP_VALUE_OR_NULL", .result = REJECT, .prog_type = BPF_PROG_TYPE_SCHED_CLS }, @@ -5304,10 +5300,8 @@ static struct bpf_test tests[] = { BPF_EXIT_INSN(), }, .fixup_map2 = { 3 }, - .errstr_unpriv = "R0 bitwise operator &= on pointer", - .errstr = "invalid mem access 'inv'", + .errstr = "R0 bitwise operator &= on pointer", .result = REJECT, - .result_unpriv = REJECT, }, { "map element value illegal alu op, 2", @@ -5323,10 +5317,8 @@ static struct bpf_test tests[] = { BPF_EXIT_INSN(), }, .fixup_map2 = { 3 }, - .errstr_unpriv = "R0 32-bit pointer arithmetic prohibited", - .errstr = "invalid mem access 'inv'", + .errstr = "R0 32-bit pointer arithmetic prohibited", .result = REJECT, - .result_unpriv = REJECT, }, { "map element value illegal alu op, 3", @@ -5342,10 +5334,8 @@ static struct bpf_test tests[] = { BPF_EXIT_INSN(), }, .fixup_map2 = { 3 }, - .errstr_unpriv = "R0 pointer arithmetic with /= operator", - .errstr = "invalid mem access 'inv'", + .errstr = "R0 pointer arithmetic with /= operator", .result = REJECT, - .result_unpriv = REJECT, }, { "map element value illegal alu op, 4", @@ -5938,8 +5928,7 @@ static struct bpf_test tests[] = { BPF_EXIT_INSN(), }, .fixup_map_in_map = { 3 }, - .errstr = "R1 type=inv expected=map_ptr", - .errstr_unpriv = "R1 pointer arithmetic on CONST_PTR_TO_MAP prohibited", + .errstr = "R1 pointer arithmetic on CONST_PTR_TO_MAP prohibited", .result = REJECT, }, { @@ -7299,6 +7288,19 @@ static struct bpf_test tests[] = { .result = REJECT, .prog_type = BPF_PROG_TYPE_SCHED_CLS, }, + { + "pkt_end - pkt_start is allowed", + .insns = { + BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1, + offsetof(struct __sk_buff, data_end)), + BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1, + offsetof(struct __sk_buff, data)), + BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_2), + BPF_EXIT_INSN(), + }, + .result = ACCEPT, + .prog_type = BPF_PROG_TYPE_SCHED_CLS, + }, { "XDP pkt read, pkt_end mangling, bad access 1", .insns = { @@ -7314,7 +7316,7 @@ static struct bpf_test tests[] = { BPF_MOV64_IMM(BPF_REG_0, 0), BPF_EXIT_INSN(), }, - .errstr = "R1 offset is outside of the packet", + .errstr = "R3 pointer arithmetic on PTR_TO_PACKET_END", .result = REJECT, .prog_type = BPF_PROG_TYPE_XDP, }, @@ -7333,7 +7335,7 @@ static struct bpf_test tests[] = { BPF_MOV64_IMM(BPF_REG_0, 0), BPF_EXIT_INSN(), }, - .errstr = "R1 offset is outside of the packet", + .errstr = "R3 pointer arithmetic on PTR_TO_PACKET_END", .result = REJECT, .prog_type = BPF_PROG_TYPE_XDP, },
From: Alexei Starovoitov ast@kernel.org
commit dd066823db2ac4e22f721ec85190817b58059a54 upstream.
Subtraction of pointers was accidentally allowed for unpriv programs by commit 82abbf8d2fc4. Revert that part of commit.
Fixes: 82abbf8d2fc4 ("bpf: do not allow root to mangle valid pointers") Reported-by: Jann Horn jannh@google.com Acked-by: Daniel Borkmann daniel@iogearbox.net Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net [fllinden@amazon.com: backport to 4.14] Signed-off-by: Frank van der Linden fllinden@amazon.com --- kernel/bpf/verifier.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index b999e268ee23..5c440398e0a1 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2754,7 +2754,7 @@ static int adjust_reg_min_max_vals(struct bpf_verifier_env *env, * an arbitrary scalar. Disallow all math except * pointer subtraction */ - if (opcode == BPF_SUB){ + if (opcode == BPF_SUB && env->allow_ptr_leaks) { mark_reg_unknown(regs, insn->dst_reg); return 0; }
From: Alexei Starovoitov ast@fb.com
commit 2b36047e7889b7efee22c11e17f035f721855731 upstream.
since commit 82abbf8d2fc4 the verifier rejects the bit-wise arithmetic on pointers earlier. The test 'dubious pointer arithmetic' now has less output to match on. Adjust it.
Fixes: 82abbf8d2fc4 ("bpf: do not allow root to mangle valid pointers") Reported-by: kernel test robot xiaolong.ye@intel.com Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net --- tools/testing/selftests/bpf/test_align.c | 22 +--------------------- 1 file changed, 1 insertion(+), 21 deletions(-)
diff --git a/tools/testing/selftests/bpf/test_align.c b/tools/testing/selftests/bpf/test_align.c index 8591c89c0828..471bbbdb94db 100644 --- a/tools/testing/selftests/bpf/test_align.c +++ b/tools/testing/selftests/bpf/test_align.c @@ -474,27 +474,7 @@ static struct bpf_align_test tests[] = { .result = REJECT, .matches = { {4, "R5=pkt(id=0,off=0,r=0,imm=0)"}, - /* ptr & 0x40 == either 0 or 0x40 */ - {5, "R5=inv(id=0,umax_value=64,var_off=(0x0; 0x40))"}, - /* ptr << 2 == unknown, (4n) */ - {7, "R5=inv(id=0,smax_value=9223372036854775804,umax_value=18446744073709551612,var_off=(0x0; 0xfffffffffffffffc))"}, - /* (4n) + 14 == (4n+2). We blow our bounds, because - * the add could overflow. - */ - {8, "R5=inv(id=0,var_off=(0x2; 0xfffffffffffffffc))"}, - /* Checked s>=0 */ - {10, "R5=inv(id=0,umin_value=2,umax_value=9223372036854775806,var_off=(0x2; 0x7ffffffffffffffc))"}, - /* packet pointer + nonnegative (4n+2) */ - {12, "R6=pkt(id=1,off=0,r=0,umin_value=2,umax_value=9223372036854775806,var_off=(0x2; 0x7ffffffffffffffc))"}, - {14, "R4=pkt(id=1,off=4,r=0,umin_value=2,umax_value=9223372036854775806,var_off=(0x2; 0x7ffffffffffffffc))"}, - /* NET_IP_ALIGN + (4n+2) == (4n), alignment is fine. - * We checked the bounds, but it might have been able - * to overflow if the packet pointer started in the - * upper half of the address space. - * So we did not get a 'range' on R6, and the access - * attempt will fail. - */ - {16, "R6=pkt(id=1,off=0,r=0,umin_value=2,umax_value=9223372036854775806,var_off=(0x2; 0x7ffffffffffffffc))"}, + /* R5 bitwise operator &= on pointer prohibited */ } }, {
From: Alexei Starovoitov ast@kernel.org
commit 31e95b61e172144bb2b626a291db1bdc0769275b upstream.
mostly revert the previous workaround and make 'dubious pointer arithmetic' test useful again. Use (ptr - ptr) << const instead of ptr << const to generate large scalar. The rest stays as before commit 2b36047e7889.
Fixes: 2b36047e7889 ("selftests/bpf: fix test_align") Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net [fllinden@amazon.com: adjust for 4.14 (no liveness of regs in output)] Signed-off-by: Frank van der Linden fllinden@amazon.com --- tools/testing/selftests/bpf/test_align.c | 30 ++++++++++++++++++------ 1 file changed, 23 insertions(+), 7 deletions(-)
diff --git a/tools/testing/selftests/bpf/test_align.c b/tools/testing/selftests/bpf/test_align.c index 471bbbdb94db..5d530c90779e 100644 --- a/tools/testing/selftests/bpf/test_align.c +++ b/tools/testing/selftests/bpf/test_align.c @@ -446,11 +446,9 @@ static struct bpf_align_test tests[] = { .insns = { PREP_PKT_POINTERS, BPF_MOV64_IMM(BPF_REG_0, 0), - /* ptr & const => unknown & const */ - BPF_MOV64_REG(BPF_REG_5, BPF_REG_2), - BPF_ALU64_IMM(BPF_AND, BPF_REG_5, 0x40), - /* ptr << const => unknown << const */ - BPF_MOV64_REG(BPF_REG_5, BPF_REG_2), + /* (ptr - ptr) << 2 */ + BPF_MOV64_REG(BPF_REG_5, BPF_REG_3), + BPF_ALU64_REG(BPF_SUB, BPF_REG_5, BPF_REG_2), BPF_ALU64_IMM(BPF_LSH, BPF_REG_5, 2), /* We have a (4n) value. Let's make a packet offset * out of it. First add 14, to make it a (4n+2) @@ -473,8 +471,26 @@ static struct bpf_align_test tests[] = { .prog_type = BPF_PROG_TYPE_SCHED_CLS, .result = REJECT, .matches = { - {4, "R5=pkt(id=0,off=0,r=0,imm=0)"}, - /* R5 bitwise operator &= on pointer prohibited */ + {4, "R5=pkt_end(id=0,off=0,imm=0)"}, + /* (ptr - ptr) << 2 == unknown, (4n) */ + {6, "R5=inv(id=0,smax_value=9223372036854775804,umax_value=18446744073709551612,var_off=(0x0; 0xfffffffffffffffc))"}, + /* (4n) + 14 == (4n+2). We blow our bounds, because + * the add could overflow. + */ + {7, "R5=inv(id=0,var_off=(0x2; 0xfffffffffffffffc))"}, + /* Checked s>=0 */ + {9, "R5=inv(id=0,umin_value=2,umax_value=9223372036854775806,var_off=(0x2; 0x7ffffffffffffffc))"}, + /* packet pointer + nonnegative (4n+2) */ + {11, "R6=pkt(id=1,off=0,r=0,umin_value=2,umax_value=9223372036854775806,var_off=(0x2; 0x7ffffffffffffffc))"}, + {13, "R4=pkt(id=1,off=4,r=0,umin_value=2,umax_value=9223372036854775806,var_off=(0x2; 0x7ffffffffffffffc))"}, + /* NET_IP_ALIGN + (4n+2) == (4n), alignment is fine. + * We checked the bounds, but it might have been able + * to overflow if the packet pointer started in the + * upper half of the address space. + * So we did not get a 'range' on R6, and the access + * attempt will fail. + */ + {15, "R6=pkt(id=1,off=0,r=0,umin_value=2,umax_value=9223372036854775806,var_off=(0x2; 0x7ffffffffffffffc))"}, } }, {
From: Daniel Borkmann daniel@iogearbox.net
commit 801c6058d14a82179a7ee17a4b532cac6fad067f upstream.
The current implemented mechanisms to mitigate data disclosure under speculation mainly address stack and map value oob access from the speculative domain. However, Piotr discovered that uninitialized BPF stack is not protected yet, and thus old data from the kernel stack, potentially including addresses of kernel structures, could still be extracted from that 512 bytes large window. The BPF stack is special compared to map values since it's not zero initialized for every program invocation, whereas map values /are/ zero initialized upon their initial allocation and thus cannot leak any prior data in either domain. In the non-speculative domain, the verifier ensures that every stack slot read must have a prior stack slot write by the BPF program to avoid such data leaking issue.
However, this is not enough: for example, when the pointer arithmetic operation moves the stack pointer from the last valid stack offset to the first valid offset, the sanitation logic allows for any intermediate offsets during speculative execution, which could then be used to extract any restricted stack content via side-channel.
Given for unprivileged stack pointer arithmetic the use of unknown but bounded scalars is generally forbidden, we can simply turn the register-based arithmetic operation into an immediate-based arithmetic operation without the need for masking. This also gives the benefit of reducing the needed instructions for the operation. Given after the work in 7fedb63a8307 ("bpf: Tighten speculative pointer arithmetic mask"), the aux->alu_limit already holds the final immediate value for the offset register with the known scalar. Thus, a simple mov of the immediate to AX register with using AX as the source for the original instruction is sufficient and possible now in this case.
Reported-by: Piotr Krysiuk piotras@gmail.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Tested-by: Piotr Krysiuk piotras@gmail.com Reviewed-by: Piotr Krysiuk piotras@gmail.com Reviewed-by: John Fastabend john.fastabend@gmail.com Acked-by: Alexei Starovoitov ast@kernel.org [fllinden@amazon.com: fixed minor 4.14 conflict because of renamed function] Signed-off-by: Frank van der Linden fllinden@amazon.com --- include/linux/bpf_verifier.h | 5 +++-- kernel/bpf/verifier.c | 27 +++++++++++++++++---------- 2 files changed, 20 insertions(+), 12 deletions(-)
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index d8b3240cfe6e..8509484cada4 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -114,10 +114,11 @@ struct bpf_verifier_state_list { };
/* Possible states for alu_state member. */ -#define BPF_ALU_SANITIZE_SRC 1U -#define BPF_ALU_SANITIZE_DST 2U +#define BPF_ALU_SANITIZE_SRC (1U << 0) +#define BPF_ALU_SANITIZE_DST (1U << 1) #define BPF_ALU_NEG_VALUE (1U << 2) #define BPF_ALU_NON_POINTER (1U << 3) +#define BPF_ALU_IMMEDIATE (1U << 4) #define BPF_ALU_SANITIZE (BPF_ALU_SANITIZE_SRC | \ BPF_ALU_SANITIZE_DST)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 5c440398e0a1..84779fe35ebc 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2120,6 +2120,7 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env, { struct bpf_insn_aux_data *aux = commit_window ? cur_aux(env) : tmp_aux; struct bpf_verifier_state *vstate = env->cur_state; + bool off_is_imm = tnum_is_const(off_reg->var_off); bool off_is_neg = off_reg->smin_value < 0; bool ptr_is_dst_reg = ptr_reg == dst_reg; u8 opcode = BPF_OP(insn->code); @@ -2150,6 +2151,7 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env, alu_limit = abs(tmp_aux->alu_limit - alu_limit); } else { alu_state = off_is_neg ? BPF_ALU_NEG_VALUE : 0; + alu_state |= off_is_imm ? BPF_ALU_IMMEDIATE : 0; alu_state |= ptr_is_dst_reg ? BPF_ALU_SANITIZE_SRC : BPF_ALU_SANITIZE_DST; } @@ -4850,7 +4852,7 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env) const u8 code_sub = BPF_ALU64 | BPF_SUB | BPF_X; struct bpf_insn insn_buf[16]; struct bpf_insn *patch = &insn_buf[0]; - bool issrc, isneg; + bool issrc, isneg, isimm; u32 off_reg;
aux = &env->insn_aux_data[i + delta]; @@ -4861,16 +4863,21 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env) isneg = aux->alu_state & BPF_ALU_NEG_VALUE; issrc = (aux->alu_state & BPF_ALU_SANITIZE) == BPF_ALU_SANITIZE_SRC; + isimm = aux->alu_state & BPF_ALU_IMMEDIATE;
off_reg = issrc ? insn->src_reg : insn->dst_reg; - if (isneg) - *patch++ = BPF_ALU64_IMM(BPF_MUL, off_reg, -1); - *patch++ = BPF_MOV32_IMM(BPF_REG_AX, aux->alu_limit); - *patch++ = BPF_ALU64_REG(BPF_SUB, BPF_REG_AX, off_reg); - *patch++ = BPF_ALU64_REG(BPF_OR, BPF_REG_AX, off_reg); - *patch++ = BPF_ALU64_IMM(BPF_NEG, BPF_REG_AX, 0); - *patch++ = BPF_ALU64_IMM(BPF_ARSH, BPF_REG_AX, 63); - *patch++ = BPF_ALU64_REG(BPF_AND, BPF_REG_AX, off_reg); + if (isimm) { + *patch++ = BPF_MOV32_IMM(BPF_REG_AX, aux->alu_limit); + } else { + if (isneg) + *patch++ = BPF_ALU64_IMM(BPF_MUL, off_reg, -1); + *patch++ = BPF_MOV32_IMM(BPF_REG_AX, aux->alu_limit); + *patch++ = BPF_ALU64_REG(BPF_SUB, BPF_REG_AX, off_reg); + *patch++ = BPF_ALU64_REG(BPF_OR, BPF_REG_AX, off_reg); + *patch++ = BPF_ALU64_IMM(BPF_NEG, BPF_REG_AX, 0); + *patch++ = BPF_ALU64_IMM(BPF_ARSH, BPF_REG_AX, 63); + *patch++ = BPF_ALU64_REG(BPF_AND, BPF_REG_AX, off_reg); + } if (!issrc) *patch++ = BPF_MOV64_REG(insn->dst_reg, insn->src_reg); insn->src_reg = BPF_REG_AX; @@ -4878,7 +4885,7 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env) insn->code = insn->code == code_add ? code_sub : code_add; *patch++ = *insn; - if (issrc && isneg) + if (issrc && isneg && !isimm) *patch++ = BPF_ALU64_IMM(BPF_MUL, off_reg, -1); cnt = patch - insn_buf;
From: Daniel Borkmann daniel@iogearbox.net
commit 3d0220f6861d713213b015b582e9f21e5b28d2e0 upstream.
Add a container structure struct bpf_sanitize_info which holds the current aux info, and update call-sites to sanitize_ptr_alu() to pass it in. This is needed for passing in additional state later on.
Signed-off-by: Daniel Borkmann daniel@iogearbox.net Reviewed-by: Piotr Krysiuk piotras@gmail.com Acked-by: Alexei Starovoitov ast@kernel.org --- kernel/bpf/verifier.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 84779fe35ebc..db359b796442 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2110,15 +2110,19 @@ static bool sanitize_needed(u8 opcode) return opcode == BPF_ADD || opcode == BPF_SUB; }
+struct bpf_sanitize_info { + struct bpf_insn_aux_data aux; +}; + static int sanitize_ptr_alu(struct bpf_verifier_env *env, struct bpf_insn *insn, const struct bpf_reg_state *ptr_reg, const struct bpf_reg_state *off_reg, struct bpf_reg_state *dst_reg, - struct bpf_insn_aux_data *tmp_aux, + struct bpf_sanitize_info *info, const bool commit_window) { - struct bpf_insn_aux_data *aux = commit_window ? cur_aux(env) : tmp_aux; + struct bpf_insn_aux_data *aux = commit_window ? cur_aux(env) : &info->aux; struct bpf_verifier_state *vstate = env->cur_state; bool off_is_imm = tnum_is_const(off_reg->var_off); bool off_is_neg = off_reg->smin_value < 0; @@ -2147,8 +2151,8 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env, /* In commit phase we narrow the masking window based on * the observed pointer move after the simulated operation. */ - alu_state = tmp_aux->alu_state; - alu_limit = abs(tmp_aux->alu_limit - alu_limit); + alu_state = info->aux.alu_state; + alu_limit = abs(info->aux.alu_limit - alu_limit); } else { alu_state = off_is_neg ? BPF_ALU_NEG_VALUE : 0; alu_state |= off_is_imm ? BPF_ALU_IMMEDIATE : 0; @@ -2276,7 +2280,7 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, smin_ptr = ptr_reg->smin_value, smax_ptr = ptr_reg->smax_value; u64 umin_val = off_reg->umin_value, umax_val = off_reg->umax_value, umin_ptr = ptr_reg->umin_value, umax_ptr = ptr_reg->umax_value; - struct bpf_insn_aux_data tmp_aux = {}; + struct bpf_sanitize_info info = {}; u8 opcode = BPF_OP(insn->code); u32 dst = insn->dst_reg; int ret; @@ -2327,7 +2331,7 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
if (sanitize_needed(opcode)) { ret = sanitize_ptr_alu(env, insn, ptr_reg, off_reg, dst_reg, - &tmp_aux, false); + &info, false); if (ret < 0) return sanitize_err(env, insn, ret, off_reg, dst_reg); } @@ -2468,7 +2472,7 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, return -EACCES; if (sanitize_needed(opcode)) { ret = sanitize_ptr_alu(env, insn, dst_reg, off_reg, dst_reg, - &tmp_aux, true); + &info, true); if (ret < 0) return sanitize_err(env, insn, ret, off_reg, dst_reg); }
From: Daniel Borkmann daniel@iogearbox.net
commit bb01a1bba579b4b1c5566af24d95f1767859771e upstream.
Masking direction as indicated via mask_to_left is considered to be calculated once and then used to derive pointer limits. Thus, this needs to be placed into bpf_sanitize_info instead so we can pass it to sanitize_ptr_alu() call after the pointer move. Piotr noticed a corner case where the off reg causes masking direction change which then results in an incorrect final aux->alu_limit.
Fixes: 7fedb63a8307 ("bpf: Tighten speculative pointer arithmetic mask") Reported-by: Piotr Krysiuk piotras@gmail.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Reviewed-by: Piotr Krysiuk piotras@gmail.com Acked-by: Alexei Starovoitov ast@kernel.org --- kernel/bpf/verifier.c | 22 ++++++++++++---------- 1 file changed, 12 insertions(+), 10 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index db359b796442..f3f14519708d 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2033,18 +2033,10 @@ enum { };
static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg, - const struct bpf_reg_state *off_reg, - u32 *alu_limit, u8 opcode) + u32 *alu_limit, bool mask_to_left) { - bool off_is_neg = off_reg->smin_value < 0; - bool mask_to_left = (opcode == BPF_ADD && off_is_neg) || - (opcode == BPF_SUB && !off_is_neg); u32 max = 0, ptr_limit = 0;
- if (!tnum_is_const(off_reg->var_off) && - (off_reg->smin_value < 0) != (off_reg->smax_value < 0)) - return REASON_BOUNDS; - switch (ptr_reg->type) { case PTR_TO_STACK: /* Offset 0 is out-of-bounds, but acceptable start for the @@ -2112,6 +2104,7 @@ static bool sanitize_needed(u8 opcode)
struct bpf_sanitize_info { struct bpf_insn_aux_data aux; + bool mask_to_left; };
static int sanitize_ptr_alu(struct bpf_verifier_env *env, @@ -2143,7 +2136,16 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env, if (vstate->speculative) goto do_sim;
- err = retrieve_ptr_limit(ptr_reg, off_reg, &alu_limit, opcode); + if (!commit_window) { + if (!tnum_is_const(off_reg->var_off) && + (off_reg->smin_value < 0) != (off_reg->smax_value < 0)) + return REASON_BOUNDS; + + info->mask_to_left = (opcode == BPF_ADD && off_is_neg) || + (opcode == BPF_SUB && !off_is_neg); + } + + err = retrieve_ptr_limit(ptr_reg, &alu_limit, info->mask_to_left); if (err < 0) return err;
From: Daniel Borkmann daniel@iogearbox.net
commit a7036191277f9fa68d92f2071ddc38c09b1e5ee5 upstream.
In 801c6058d14a ("bpf: Fix leakage of uninitialized bpf stack under speculation") we replaced masking logic with direct loads of immediates if the register is a known constant. Given in this case we do not apply any masking, there is also no reason for the operation to be truncated under the speculative domain.
Therefore, there is also zero reason for the verifier to branch-off and simulate this case, it only needs to do it for unknown but bounded scalars. As a side-effect, this also enables few test cases that were previously rejected due to simulation under zero truncation.
Signed-off-by: Daniel Borkmann daniel@iogearbox.net Reviewed-by: Piotr Krysiuk piotras@gmail.com Acked-by: Alexei Starovoitov ast@kernel.org --- kernel/bpf/verifier.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index f3f14519708d..4a3333039bf2 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2169,8 +2169,12 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env, /* If we're in commit phase, we're done here given we already * pushed the truncated dst_reg into the speculative verification * stack. + * + * Also, when register is a known constant, we rewrite register-based + * operation to immediate-based, and thus do not need masking (and as + * a consequence, do not need to simulate the zero-truncation either). */ - if (commit_window) + if (commit_window || off_is_imm) return 0;
/* Simulate and find potential out-of-bounds access under
On Mon, May 31, 2021 at 06:25:39PM +0000, Frank van der Linden wrote:
Now that these are being included in 4.19, I am resending this 4.14 series. It was originally sent here:
https://lore.kernel.org/bpf/20210501043014.33300-5-fllinden@amazon.com/T/
v2:
The backport repairs in that original series were already included in 4.14, so they are no longer needed.
Add additional commit for CVE-2021-31829.
Added cherry-picks for CVE-2021-33200.
All now qeueud up, thanks.
greg k-h
linux-stable-mirror@lists.linaro.org
-
Frank van der Linden -
Greg KH