From: Vincenzo Frascino <[email protected]> When we invoke strscpy() with a maximum size of N bytes, it assumes that: - It can always read N bytes from the source. - It always write N bytes (zero-padded) to the destination.
On aarch64 with Memory Tagging Extension enabled if we pass an N that is bigger then the source buffer, it triggers an MTE fault. Implement a KASAN KUnit test that triggers the issue with the current implementation of read_word_at_a_time() on aarch64 with MTE enabled. Cc: Will Deacon <[email protected]> Signed-off-by: Vincenzo Frascino <[email protected]> Signed-off-by: Catalin Marinas <[email protected]> Co-developed-by: Peter Collingbourne <[email protected]> Signed-off-by: Peter Collingbourne <[email protected]> Link: https://linux-review.googlesource.com/id/If88e396b9e7c058c1a4b5a252274120e77b1898a --- v2: - rebased - fixed test failure mm/kasan/kasan_test_c.c | 31 ++++++++++++++++++++++++++++++- 1 file changed, 30 insertions(+), 1 deletion(-) diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c index 59d673400085f..c4bb3ee497b54 100644 --- a/mm/kasan/kasan_test_c.c +++ b/mm/kasan/kasan_test_c.c @@ -1570,7 +1570,9 @@ static void kasan_memcmp(struct kunit *test) static void kasan_strings(struct kunit *test) { char *ptr; - size_t size = 24; + char *src, *src2; + u8 tag; + size_t size = 2 * KASAN_GRANULE_SIZE; /* * str* functions are not instrumented with CONFIG_AMD_MEM_ENCRYPT. @@ -1581,6 +1583,33 @@ static void kasan_strings(struct kunit *test) ptr = kmalloc(size, GFP_KERNEL | __GFP_ZERO); KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr); + src = kmalloc(size, GFP_KERNEL | __GFP_ZERO); + strscpy(src, "f0cacc1a00000000f0cacc1a00000000", size); + + tag = get_tag(src); + + src2 = src + KASAN_GRANULE_SIZE; + + /* + * Shorten string and poison the granule after it so that the unaligned + * read in strscpy() triggers a tag mismatch. + */ + src[KASAN_GRANULE_SIZE - 1] = '\0'; + kasan_poison(src2, KASAN_GRANULE_SIZE, tag + 1, false); + + /* + * The expected size does not include the terminator '\0' + * so it is (KASAN_GRANULE_SIZE - 2) == + * KASAN_GRANULE_SIZE - ("initial removed character" + "\0"). + */ + KUNIT_EXPECT_EQ(test, KASAN_GRANULE_SIZE - 2, + strscpy(ptr, src + 1, size)); + + /* Undo operations above. */ + src[KASAN_GRANULE_SIZE - 1] = '0'; + kasan_poison(src2, KASAN_GRANULE_SIZE, tag, false); + + kfree(src); kfree(ptr); /* -- 2.49.0.395.g12beb8f557-goog
