From 758cabae312d3aded781aacc6d0c946b299c52df Mon Sep 17 00:00:00 2001 From: Peter Collingbourne Date: Fri, 5 Nov 2021 13:35:56 -0700 Subject: kasan: test: add memcpy test that avoids out-of-bounds write With HW tag-based KASAN, error checks are performed implicitly by the load and store instructions in the memcpy implementation. A failed check results in tag checks being disabled and execution will keep going. As a result, under HW tag-based KASAN, prior to commit 1b0668be62cf ("kasan: test: disable kmalloc_memmove_invalid_size for HW_TAGS"), this memcpy would end up corrupting memory until it hits an inaccessible page and causes a kernel panic. This is a pre-existing issue that was revealed by commit 285133040e6c ("arm64: Import latest memcpy()/memmove() implementation") which changed the memcpy implementation from using signed comparisons (incorrectly, resulting in the memcpy being terminated early for negative sizes) to using unsigned comparisons. It is unclear how this could be handled by memcpy itself in a reasonable way. One possibility would be to add an exception handler that would force memcpy to return if a tag check fault is detected -- this would make the behavior roughly similar to generic and SW tag-based KASAN. However, this wouldn't solve the problem for asynchronous mode and also makes memcpy behavior inconsistent with manually copying data. This test was added as a part of a series that taught KASAN to detect negative sizes in memory operations, see commit 8cceeff48f23 ("kasan: detect negative size in memory operation function"). Therefore we should keep testing for negative sizes with generic and SW tag-based KASAN. But there is some value in testing small memcpy overflows, so let's add another test with memcpy that does not destabilize the kernel by performing out-of-bounds writes, and run it in all modes. Link: https://linux-review.googlesource.com/id/I048d1e6a9aff766c4a53f989fb0c83de68923882 Link: https://lkml.kernel.org/r/20210910211356.3603758-1-pcc@google.com Signed-off-by: Peter Collingbourne Reviewed-by: Andrey Konovalov Acked-by: Marco Elver Cc: Robin Murphy Cc: Will Deacon Cc: Catalin Marinas Cc: Mark Rutland Cc: Evgenii Stepanov Cc: Alexander Potapenko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- lib/test_kasan.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) (limited to 'lib/test_kasan.c') diff --git a/lib/test_kasan.c b/lib/test_kasan.c index 8835e0784578..aa8e42250219 100644 --- a/lib/test_kasan.c +++ b/lib/test_kasan.c @@ -493,7 +493,7 @@ static void kmalloc_oob_in_memset(struct kunit *test) kfree(ptr); } -static void kmalloc_memmove_invalid_size(struct kunit *test) +static void kmalloc_memmove_negative_size(struct kunit *test) { char *ptr; size_t size = 64; @@ -515,6 +515,21 @@ static void kmalloc_memmove_invalid_size(struct kunit *test) kfree(ptr); } +static void kmalloc_memmove_invalid_size(struct kunit *test) +{ + char *ptr; + size_t size = 64; + volatile size_t invalid_size = size; + + ptr = kmalloc(size, GFP_KERNEL); + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr); + + memset((char *)ptr, 0, 64); + KUNIT_EXPECT_KASAN_FAIL(test, + memmove((char *)ptr, (char *)ptr + 4, invalid_size)); + kfree(ptr); +} + static void kmalloc_uaf(struct kunit *test) { char *ptr; @@ -1129,6 +1144,7 @@ static struct kunit_case kasan_kunit_test_cases[] = { KUNIT_CASE(kmalloc_oob_memset_4), KUNIT_CASE(kmalloc_oob_memset_8), KUNIT_CASE(kmalloc_oob_memset_16), + KUNIT_CASE(kmalloc_memmove_negative_size), KUNIT_CASE(kmalloc_memmove_invalid_size), KUNIT_CASE(kmalloc_uaf), KUNIT_CASE(kmalloc_uaf_memset), -- cgit v1.2.3 From d73dad4eb5ad8c31ac9cf358eb5a55825bafe706 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Fri, 5 Nov 2021 13:36:12 -0700 Subject: kasan: test: bypass __alloc_size checks Intentional overflows, as performed by the KASAN tests, are detected at compile time[1] (instead of only at run-time) with the addition of __alloc_size. Fix this by forcing the compiler into not being able to trust the size used following the kmalloc()s. [1] https://lore.kernel.org/lkml/20211005184717.65c6d8eb39350395e387b71f@linux-foundation.org Link: https://lkml.kernel.org/r/20211006181544.1670992-1-keescook@chromium.org Signed-off-by: Kees Cook Cc: Andrey Ryabinin Cc: Alexander Potapenko Cc: Andrey Konovalov Cc: Dmitry Vyukov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- lib/test_kasan.c | 8 +++++++- lib/test_kasan_module.c | 2 ++ 2 files changed, 9 insertions(+), 1 deletion(-) (limited to 'lib/test_kasan.c') diff --git a/lib/test_kasan.c b/lib/test_kasan.c index aa8e42250219..5475fe396ff7 100644 --- a/lib/test_kasan.c +++ b/lib/test_kasan.c @@ -440,6 +440,7 @@ static void kmalloc_oob_memset_2(struct kunit *test) ptr = kmalloc(size, GFP_KERNEL); KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr); + OPTIMIZER_HIDE_VAR(size); KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 1, 0, 2)); kfree(ptr); } @@ -452,6 +453,7 @@ static void kmalloc_oob_memset_4(struct kunit *test) ptr = kmalloc(size, GFP_KERNEL); KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr); + OPTIMIZER_HIDE_VAR(size); KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 3, 0, 4)); kfree(ptr); } @@ -464,6 +466,7 @@ static void kmalloc_oob_memset_8(struct kunit *test) ptr = kmalloc(size, GFP_KERNEL); KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr); + OPTIMIZER_HIDE_VAR(size); KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 7, 0, 8)); kfree(ptr); } @@ -476,6 +479,7 @@ static void kmalloc_oob_memset_16(struct kunit *test) ptr = kmalloc(size, GFP_KERNEL); KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr); + OPTIMIZER_HIDE_VAR(size); KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 15, 0, 16)); kfree(ptr); } @@ -488,6 +492,7 @@ static void kmalloc_oob_in_memset(struct kunit *test) ptr = kmalloc(size, GFP_KERNEL); KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr); + OPTIMIZER_HIDE_VAR(size); KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr, 0, size + KASAN_GRANULE_SIZE)); kfree(ptr); @@ -497,7 +502,7 @@ static void kmalloc_memmove_negative_size(struct kunit *test) { char *ptr; size_t size = 64; - volatile size_t invalid_size = -2; + size_t invalid_size = -2; /* * Hardware tag-based mode doesn't check memmove for negative size. @@ -510,6 +515,7 @@ static void kmalloc_memmove_negative_size(struct kunit *test) KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr); memset((char *)ptr, 0, 64); + OPTIMIZER_HIDE_VAR(invalid_size); KUNIT_EXPECT_KASAN_FAIL(test, memmove((char *)ptr, (char *)ptr + 4, invalid_size)); kfree(ptr); diff --git a/lib/test_kasan_module.c b/lib/test_kasan_module.c index 7ebf433edef3..b112cbc835e9 100644 --- a/lib/test_kasan_module.c +++ b/lib/test_kasan_module.c @@ -35,6 +35,8 @@ static noinline void __init copy_user_test(void) return; } + OPTIMIZER_HIDE_VAR(size); + pr_info("out-of-bounds in copy_from_user()\n"); unused = copy_from_user(kmem, usermem, size + 1); -- cgit v1.2.3