Hi Greg,
(Since this was aleady pending, I just spun a v2, resent here.)
Can you please apply these patches to your drivers/misc tree for LKDTM? It's mostly a collection of fixes and improvements and tweaks to the selftest integration.
Thanks!
-Kees
v2: - add fix for UML build failures (Randy, Richard) v1: https://lore.kernel.org/lkml/20200529200347.2464284-1-keescook@chromium.org/
Kees Cook (4): lkdtm: Avoid more compiler optimizations for bad writes lkdtm/heap: Avoid edge and middle of slabs selftests/lkdtm: Reset WARN_ONCE to avoid false negatives lkdtm: Make arch-specific tests always available
drivers/misc/lkdtm/bugs.c | 49 +++++++++++++------------ drivers/misc/lkdtm/heap.c | 9 +++-- drivers/misc/lkdtm/lkdtm.h | 2 - drivers/misc/lkdtm/perms.c | 22 +++++++---- drivers/misc/lkdtm/usercopy.c | 7 +++- tools/testing/selftests/lkdtm/run.sh | 6 +++ tools/testing/selftests/lkdtm/tests.txt | 1 + 7 files changed, 58 insertions(+), 38 deletions(-)
It seems at least Clang is able to throw away writes it knows are destined for read-only memory, which makes things like the WRITE_RO test fail, as the write gets elided. Instead, force the variable to be volatile, and make similar changes through-out other tests in an effort to avoid needing to repeat fixing these kinds of problems. Also includes pr_err() calls in failure paths so that kernel logs are more clear in the failure case.
Reported-by: Prasad Sodagudi psodagud@codeaurora.org Suggested-by: Sami Tolvanen samitolvanen@google.com Fixes: 9ae113ce5faf ("lkdtm: add tests for additional page permissions") Signed-off-by: Kees Cook keescook@chromium.org --- drivers/misc/lkdtm/bugs.c | 11 +++++------ drivers/misc/lkdtm/perms.c | 22 +++++++++++++++------- drivers/misc/lkdtm/usercopy.c | 7 +++++-- 3 files changed, 25 insertions(+), 15 deletions(-)
diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c index 736675f0a246..08c70281c380 100644 --- a/drivers/misc/lkdtm/bugs.c +++ b/drivers/misc/lkdtm/bugs.c @@ -118,9 +118,8 @@ noinline void lkdtm_CORRUPT_STACK(void) /* Use default char array length that triggers stack protection. */ char data[8] __aligned(sizeof(void *));
- __lkdtm_CORRUPT_STACK(&data); - - pr_info("Corrupted stack containing char array ...\n"); + pr_info("Corrupting stack containing char array ...\n"); + __lkdtm_CORRUPT_STACK((void *)&data); }
/* Same as above but will only get a canary with -fstack-protector-strong */ @@ -131,9 +130,8 @@ noinline void lkdtm_CORRUPT_STACK_STRONG(void) unsigned long *ptr; } data __aligned(sizeof(void *));
- __lkdtm_CORRUPT_STACK(&data); - - pr_info("Corrupted stack containing union ...\n"); + pr_info("Corrupting stack containing union ...\n"); + __lkdtm_CORRUPT_STACK((void *)&data); }
void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void) @@ -248,6 +246,7 @@ void lkdtm_ARRAY_BOUNDS(void)
kfree(not_checked); kfree(checked); + pr_err("FAIL: survived array bounds overflow!\n"); }
void lkdtm_CORRUPT_LIST_ADD(void) diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c index 62f76d506f04..2dede2ef658f 100644 --- a/drivers/misc/lkdtm/perms.c +++ b/drivers/misc/lkdtm/perms.c @@ -57,6 +57,7 @@ static noinline void execute_location(void *dst, bool write) } pr_info("attempting bad execution at %px\n", func); func(); + pr_err("FAIL: func returned\n"); }
static void execute_user_location(void *dst) @@ -75,20 +76,22 @@ static void execute_user_location(void *dst) return; pr_info("attempting bad execution at %px\n", func); func(); + pr_err("FAIL: func returned\n"); }
void lkdtm_WRITE_RO(void) { - /* Explicitly cast away "const" for the test. */ - unsigned long *ptr = (unsigned long *)&rodata; + /* Explicitly cast away "const" for the test and make volatile. */ + volatile unsigned long *ptr = (unsigned long *)&rodata;
pr_info("attempting bad rodata write at %px\n", ptr); *ptr ^= 0xabcd1234; + pr_err("FAIL: survived bad write\n"); }
void lkdtm_WRITE_RO_AFTER_INIT(void) { - unsigned long *ptr = &ro_after_init; + volatile unsigned long *ptr = &ro_after_init;
/* * Verify we were written to during init. Since an Oops @@ -102,19 +105,21 @@ void lkdtm_WRITE_RO_AFTER_INIT(void)
pr_info("attempting bad ro_after_init write at %px\n", ptr); *ptr ^= 0xabcd1234; + pr_err("FAIL: survived bad write\n"); }
void lkdtm_WRITE_KERN(void) { size_t size; - unsigned char *ptr; + volatile unsigned char *ptr;
size = (unsigned long)do_overwritten - (unsigned long)do_nothing; ptr = (unsigned char *)do_overwritten;
pr_info("attempting bad %zu byte write at %px\n", size, ptr); - memcpy(ptr, (unsigned char *)do_nothing, size); + memcpy((void *)ptr, (unsigned char *)do_nothing, size); flush_icache_range((unsigned long)ptr, (unsigned long)(ptr + size)); + pr_err("FAIL: survived bad write\n");
do_overwritten(); } @@ -193,9 +198,11 @@ void lkdtm_ACCESS_USERSPACE(void) pr_info("attempting bad read at %px\n", ptr); tmp = *ptr; tmp += 0xc0dec0de; + pr_err("FAIL: survived bad read\n");
pr_info("attempting bad write at %px\n", ptr); *ptr = tmp; + pr_err("FAIL: survived bad write\n");
vm_munmap(user_addr, PAGE_SIZE); } @@ -203,19 +210,20 @@ void lkdtm_ACCESS_USERSPACE(void) void lkdtm_ACCESS_NULL(void) { unsigned long tmp; - unsigned long *ptr = (unsigned long *)NULL; + volatile unsigned long *ptr = (unsigned long *)NULL;
pr_info("attempting bad read at %px\n", ptr); tmp = *ptr; tmp += 0xc0dec0de; + pr_err("FAIL: survived bad read\n");
pr_info("attempting bad write at %px\n", ptr); *ptr = tmp; + pr_err("FAIL: survived bad write\n"); }
void __init lkdtm_perms_init(void) { /* Make sure we can write to __ro_after_init values during __init */ ro_after_init |= 0xAA; - } diff --git a/drivers/misc/lkdtm/usercopy.c b/drivers/misc/lkdtm/usercopy.c index e172719dd86d..b833367a45d0 100644 --- a/drivers/misc/lkdtm/usercopy.c +++ b/drivers/misc/lkdtm/usercopy.c @@ -304,19 +304,22 @@ void lkdtm_USERCOPY_KERNEL(void) return; }
- pr_info("attempting good copy_to_user from kernel rodata\n"); + pr_info("attempting good copy_to_user from kernel rodata: %px\n", + test_text); if (copy_to_user((void __user *)user_addr, test_text, unconst + sizeof(test_text))) { pr_warn("copy_to_user failed unexpectedly?!\n"); goto free_user; }
- pr_info("attempting bad copy_to_user from kernel text\n"); + pr_info("attempting bad copy_to_user from kernel text: %px\n", + vm_mmap); if (copy_to_user((void __user *)user_addr, vm_mmap, unconst + PAGE_SIZE)) { pr_warn("copy_to_user failed, but lacked Oops\n"); goto free_user; } + pr_err("FAIL: survived bad copy_to_user()\n");
free_user: vm_munmap(user_addr, PAGE_SIZE);
Har har, after I moved the slab freelist pointer into the middle of the slab, now it looks like the contents are getting poisoned. Adjust the test to avoid the freelist pointer again.
Fixes: 3202fa62fb43 ("slub: relocate freelist pointer to middle of object") Cc: stable@vger.kernel.org Signed-off-by: Kees Cook keescook@chromium.org --- drivers/misc/lkdtm/heap.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/drivers/misc/lkdtm/heap.c b/drivers/misc/lkdtm/heap.c index 3c5cec85edce..1323bc16f113 100644 --- a/drivers/misc/lkdtm/heap.c +++ b/drivers/misc/lkdtm/heap.c @@ -58,11 +58,12 @@ void lkdtm_READ_AFTER_FREE(void) int *base, *val, saw; size_t len = 1024; /* - * The slub allocator uses the first word to store the free - * pointer in some configurations. Use the middle of the - * allocation to avoid running into the freelist + * The slub allocator will use the either the first word or + * the middle of the allocation to store the free pointer, + * depending on configurations. Store in the second word to + * avoid running into the freelist. */ - size_t offset = (len / sizeof(*base)) / 2; + size_t offset = sizeof(*base);
base = kmalloc(len, GFP_KERNEL); if (!base) {
Since we expect to see warnings every time for many tests, just reset the WARN_ONCE flags each time the script runs.
Fixes: 46d1a0f03d66 ("selftests/lkdtm: Add tests for LKDTM targets") Signed-off-by: Kees Cook keescook@chromium.org --- tools/testing/selftests/lkdtm/run.sh | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/tools/testing/selftests/lkdtm/run.sh b/tools/testing/selftests/lkdtm/run.sh index ee64ff8df8f4..8383eb89d88a 100755 --- a/tools/testing/selftests/lkdtm/run.sh +++ b/tools/testing/selftests/lkdtm/run.sh @@ -8,6 +8,7 @@ # set -e TRIGGER=/sys/kernel/debug/provoke-crash/DIRECT +CLEAR_ONCE=/sys/kernel/debug/clear_warn_once KSELFTEST_SKIP_TEST=4
# Verify we have LKDTM available in the kernel. @@ -67,6 +68,11 @@ cleanup() { } trap cleanup EXIT
+# Reset WARN_ONCE counters so we trip it each time this runs. +if [ -w $CLEAR_ONCE ] ; then + echo 1 > $CLEAR_ONCE +fi + # Save existing dmesg so we can detect new content below dmesg > "$DMESG"
I'd like arch-specific tests to XFAIL when on a mismatched architecture so that we can more easily compare test coverage across all systems. Lacking kernel configs or CPU features count as a FAIL, not an XFAIL.
Additionally fixes a build failure under 32-bit UML.
Fixes: b09511c253e5 ("lkdtm: Add a DOUBLE_FAULT crash type on x86") Fixes: cea23efb4de2 ("lkdtm/bugs: Make double-fault test always available") Fixes: 6cb6982f42cb ("lkdtm: arm64: test kernel pointer authentication") Signed-off-by: Kees Cook keescook@chromium.org --- drivers/misc/lkdtm/bugs.c | 38 ++++++++++++++----------- drivers/misc/lkdtm/lkdtm.h | 2 -- tools/testing/selftests/lkdtm/tests.txt | 1 + 3 files changed, 22 insertions(+), 19 deletions(-)
diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c index 08c70281c380..10338800f6be 100644 --- a/drivers/misc/lkdtm/bugs.c +++ b/drivers/misc/lkdtm/bugs.c @@ -13,7 +13,7 @@ #include <linux/uaccess.h> #include <linux/slab.h>
-#ifdef CONFIG_X86_32 +#if IS_ENABLED(CONFIG_X86_32) && !IS_ENABLED(CONFIG_UML) #include <asm/desc.h> #endif
@@ -418,7 +418,7 @@ void lkdtm_UNSET_SMEP(void)
void lkdtm_DOUBLE_FAULT(void) { -#ifdef CONFIG_X86_32 +#if IS_ENABLED(CONFIG_X86_32) && !IS_ENABLED(CONFIG_UML) /* * Trigger #DF by setting the stack limit to zero. This clobbers * a GDT TLS slot, which is okay because the current task will die @@ -453,38 +453,42 @@ void lkdtm_DOUBLE_FAULT(void) #endif }
-#ifdef CONFIG_ARM64_PTR_AUTH +#ifdef CONFIG_ARM64 static noinline void change_pac_parameters(void) { - /* Reset the keys of current task */ - ptrauth_thread_init_kernel(current); - ptrauth_thread_switch_kernel(current); + if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH)) { + /* Reset the keys of current task */ + ptrauth_thread_init_kernel(current); + ptrauth_thread_switch_kernel(current); + } } +#endif
-#define CORRUPT_PAC_ITERATE 10 noinline void lkdtm_CORRUPT_PAC(void) { +#ifdef CONFIG_ARM64 +#define CORRUPT_PAC_ITERATE 10 int i;
+ if (!IS_ENABLED(CONFIG_ARM64_PTR_AUTH)) + pr_err("FAIL: kernel not built with CONFIG_ARM64_PTR_AUTH\n"); + if (!system_supports_address_auth()) { - pr_err("FAIL: arm64 pointer authentication feature not present\n"); + pr_err("FAIL: CPU lacks pointer authentication feature\n"); return; }
- pr_info("Change the PAC parameters to force function return failure\n"); + pr_info("changing PAC parameters to force function return failure...\n"); /* - * Pac is a hash value computed from input keys, return address and + * PAC is a hash value computed from input keys, return address and * stack pointer. As pac has fewer bits so there is a chance of * collision, so iterate few times to reduce the collision probability. */ for (i = 0; i < CORRUPT_PAC_ITERATE; i++) change_pac_parameters();
- pr_err("FAIL: %s test failed. Kernel may be unstable from here\n", __func__); -} -#else /* !CONFIG_ARM64_PTR_AUTH */ -noinline void lkdtm_CORRUPT_PAC(void) -{ - pr_err("FAIL: arm64 pointer authentication config disabled\n"); -} + pr_err("FAIL: survived PAC changes! Kernel may be unstable from here\n"); +#else + pr_err("XFAIL: this test is arm64-only\n"); #endif +} diff --git a/drivers/misc/lkdtm/lkdtm.h b/drivers/misc/lkdtm/lkdtm.h index 601a2156a0d4..8878538b2c13 100644 --- a/drivers/misc/lkdtm/lkdtm.h +++ b/drivers/misc/lkdtm/lkdtm.h @@ -31,9 +31,7 @@ void lkdtm_CORRUPT_USER_DS(void); void lkdtm_STACK_GUARD_PAGE_LEADING(void); void lkdtm_STACK_GUARD_PAGE_TRAILING(void); void lkdtm_UNSET_SMEP(void); -#ifdef CONFIG_X86_32 void lkdtm_DOUBLE_FAULT(void); -#endif void lkdtm_CORRUPT_PAC(void);
/* lkdtm_heap.c */ diff --git a/tools/testing/selftests/lkdtm/tests.txt b/tools/testing/selftests/lkdtm/tests.txt index 92ca32143ae5..9d266e79c6a2 100644 --- a/tools/testing/selftests/lkdtm/tests.txt +++ b/tools/testing/selftests/lkdtm/tests.txt @@ -14,6 +14,7 @@ STACK_GUARD_PAGE_LEADING STACK_GUARD_PAGE_TRAILING UNSET_SMEP CR4 bits went missing DOUBLE_FAULT +CORRUPT_PAC UNALIGNED_LOAD_STORE_WRITE #OVERWRITE_ALLOCATION Corrupts memory on failure #WRITE_AFTER_FREE Corrupts memory on failure
linux-kselftest-mirror@lists.linaro.org
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Kees Cook