From: Andrii Nakryiko andrii@kernel.org
[ Upstream commit 1ef22b6865a73a8aed36d43375fe8c7b30869326 ]
Teach __mark_chain_precision logic to maintain register/stack masks across all active frames when going from child state to parent state. Currently this should be mostly no-op, as precision backtracking usually bails out when encountering subprog entry/exit.
It's not very apparent from the diff due to increased indentation, but the logic remains the same, except everything is done on specific `fr` frame index. Calls to bt_clear_reg() and bt_clear_slot() are replaced with frame-specific bt_clear_frame_reg() and bt_clear_frame_slot(), where frame index is passed explicitly, instead of using current frame number.
We also adjust logging to emit affected frame number. And we also add better logging of human-readable register and stack slot masks, similar to previous patch.
Signed-off-by: Andrii Nakryiko andrii@kernel.org Link: https://lore.kernel.org/r/20230505043317.3629845-6-andrii@kernel.org Signed-off-by: Alexei Starovoitov ast@kernel.org Stable-dep-of: f655badf2a8f ("bpf: fix propagate_precision() logic for inner frames") Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/verifier.c | 100 ++++++++++-------- .../testing/selftests/bpf/verifier/precise.c | 18 ++-- 2 files changed, 62 insertions(+), 56 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 9260006c13823..bc4cf078e6277 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -3694,7 +3694,7 @@ static int __mark_chain_precision(struct bpf_verifier_env *env, int frame, int r struct bpf_func_state *func; struct bpf_reg_state *reg; bool skip_first = true; - int i, err; + int i, fr, err;
if (!env->bpf_capable) return 0; @@ -3803,56 +3803,62 @@ static int __mark_chain_precision(struct bpf_verifier_env *env, int frame, int r if (!st) break;
- func = st->frame[frame]; - bitmap_from_u64(mask, bt_reg_mask(bt)); - for_each_set_bit(i, mask, 32) { - reg = &func->regs[i]; - if (reg->type != SCALAR_VALUE) { - bt_clear_reg(bt, i); - continue; + for (fr = bt->frame; fr >= 0; fr--) { + func = st->frame[fr]; + bitmap_from_u64(mask, bt_frame_reg_mask(bt, fr)); + for_each_set_bit(i, mask, 32) { + reg = &func->regs[i]; + if (reg->type != SCALAR_VALUE) { + bt_clear_frame_reg(bt, fr, i); + continue; + } + if (reg->precise) + bt_clear_frame_reg(bt, fr, i); + else + reg->precise = true; } - if (reg->precise) - bt_clear_reg(bt, i); - else - reg->precise = true; - }
- bitmap_from_u64(mask, bt_stack_mask(bt)); - for_each_set_bit(i, mask, 64) { - if (i >= func->allocated_stack / BPF_REG_SIZE) { - /* the sequence of instructions: - * 2: (bf) r3 = r10 - * 3: (7b) *(u64 *)(r3 -8) = r0 - * 4: (79) r4 = *(u64 *)(r10 -8) - * doesn't contain jmps. It's backtracked - * as a single block. - * During backtracking insn 3 is not recognized as - * stack access, so at the end of backtracking - * stack slot fp-8 is still marked in stack_mask. - * However the parent state may not have accessed - * fp-8 and it's "unallocated" stack space. - * In such case fallback to conservative. - */ - mark_all_scalars_precise(env, st); - bt_reset(bt); - return 0; - } + bitmap_from_u64(mask, bt_frame_stack_mask(bt, fr)); + for_each_set_bit(i, mask, 64) { + if (i >= func->allocated_stack / BPF_REG_SIZE) { + /* the sequence of instructions: + * 2: (bf) r3 = r10 + * 3: (7b) *(u64 *)(r3 -8) = r0 + * 4: (79) r4 = *(u64 *)(r10 -8) + * doesn't contain jmps. It's backtracked + * as a single block. + * During backtracking insn 3 is not recognized as + * stack access, so at the end of backtracking + * stack slot fp-8 is still marked in stack_mask. + * However the parent state may not have accessed + * fp-8 and it's "unallocated" stack space. + * In such case fallback to conservative. + */ + mark_all_scalars_precise(env, st); + bt_reset(bt); + return 0; + }
- if (!is_spilled_scalar_reg(&func->stack[i])) { - bt_clear_slot(bt, i); - continue; + if (!is_spilled_scalar_reg(&func->stack[i])) { + bt_clear_frame_slot(bt, fr, i); + continue; + } + reg = &func->stack[i].spilled_ptr; + if (reg->precise) + bt_clear_frame_slot(bt, fr, i); + else + reg->precise = true; + } + if (env->log.level & BPF_LOG_LEVEL2) { + fmt_reg_mask(env->tmp_str_buf, TMP_STR_BUF_LEN, + bt_frame_reg_mask(bt, fr)); + verbose(env, "mark_precise: frame%d: parent state regs=%s ", + fr, env->tmp_str_buf); + fmt_stack_mask(env->tmp_str_buf, TMP_STR_BUF_LEN, + bt_frame_stack_mask(bt, fr)); + verbose(env, "stack=%s: ", env->tmp_str_buf); + print_verifier_state(env, func, true); } - reg = &func->stack[i].spilled_ptr; - if (reg->precise) - bt_clear_slot(bt, i); - else - reg->precise = true; - } - if (env->log.level & BPF_LOG_LEVEL2) { - verbose(env, "parent %s regs=%x stack=%llx marks:", - !bt_empty(bt) ? "didn't have" : "already had", - bt_reg_mask(bt), bt_stack_mask(bt)); - print_verifier_state(env, func, true); }
if (bt_empty(bt)) diff --git a/tools/testing/selftests/bpf/verifier/precise.c b/tools/testing/selftests/bpf/verifier/precise.c index 86cb0722792f0..a928c53432999 100644 --- a/tools/testing/selftests/bpf/verifier/precise.c +++ b/tools/testing/selftests/bpf/verifier/precise.c @@ -44,7 +44,7 @@ mark_precise: frame0: regs=r2 stack= before 23\ mark_precise: frame0: regs=r2 stack= before 22\ mark_precise: frame0: regs=r2 stack= before 20\ - parent didn't have regs=4 stack=0 marks:\ + mark_precise: frame0: parent state regs=r2 stack=:\ mark_precise: frame0: last_idx 19 first_idx 10\ mark_precise: frame0: regs=r2 stack= before 19\ mark_precise: frame0: regs=r9 stack= before 18\ @@ -55,7 +55,7 @@ mark_precise: frame0: regs=r9 stack= before 12\ mark_precise: frame0: regs=r9 stack= before 11\ mark_precise: frame0: regs=r9 stack= before 10\ - parent already had regs=0 stack=0 marks:", + mark_precise: frame0: parent state regs= stack=:", }, { "precise: test 2", @@ -104,15 +104,15 @@ mark_precise: frame0: regs=r2 stack= before 24\ mark_precise: frame0: regs=r2 stack= before 23\ mark_precise: frame0: regs=r2 stack= before 22\ - parent didn't have regs=4 stack=0 marks:\ + mark_precise: frame0: parent state regs=r2 stack=:\ mark_precise: frame0: last_idx 20 first_idx 20\ mark_precise: frame0: regs=r2 stack= before 20\ - parent didn't have regs=4 stack=0 marks:\ + mark_precise: frame0: parent state regs=r2 stack=:\ mark_precise: frame0: last_idx 19 first_idx 17\ mark_precise: frame0: regs=r2 stack= before 19\ mark_precise: frame0: regs=r9 stack= before 18\ mark_precise: frame0: regs=r8,r9 stack= before 17\ - parent already had regs=0 stack=0 marks:", + mark_precise: frame0: parent state regs= stack=:", }, { "precise: cross frame pruning", @@ -153,14 +153,14 @@ .prog_type = BPF_PROG_TYPE_XDP, .flags = BPF_F_TEST_STATE_FREQ, .errstr = "mark_precise: frame0: last_idx 5 first_idx 5\ - parent didn't have regs=10 stack=0 marks:\ + mark_precise: frame0: parent state regs=r4 stack=:\ mark_precise: frame0: last_idx 4 first_idx 2\ mark_precise: frame0: regs=r4 stack= before 4\ mark_precise: frame0: regs=r4 stack= before 3\ mark_precise: frame0: regs= stack=-8 before 2\ mark_precise: frame0: falling back to forcing all scalars precise\ mark_precise: frame0: last_idx 5 first_idx 5\ - parent didn't have regs=1 stack=0 marks:", + mark_precise: frame0: parent state regs=r0 stack=:", .result = VERBOSE_ACCEPT, .retval = -1, }, @@ -179,7 +179,7 @@ .prog_type = BPF_PROG_TYPE_XDP, .flags = BPF_F_TEST_STATE_FREQ, .errstr = "mark_precise: frame0: last_idx 6 first_idx 6\ - parent didn't have regs=10 stack=0 marks:\ + mark_precise: frame0: parent state regs=r4 stack=:\ mark_precise: frame0: last_idx 5 first_idx 3\ mark_precise: frame0: regs=r4 stack= before 5\ mark_precise: frame0: regs=r4 stack= before 4\ @@ -188,7 +188,7 @@ force_precise: frame0: forcing r0 to be precise\ force_precise: frame0: forcing r0 to be precise\ mark_precise: frame0: last_idx 6 first_idx 6\ - parent didn't have regs=1 stack=0 marks:\ + mark_precise: frame0: parent state regs=r0 stack=:\ mark_precise: frame0: last_idx 5 first_idx 3\ mark_precise: frame0: regs=r0 stack= before 5", .result = VERBOSE_ACCEPT,