From: Vincenzo Frascino <vincenzo.frasc...@arm.com> 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 would previously trigger an MTE fault. Implement a KASAN KUnit test that triggers the issue with the previous implementation of read_word_at_a_time() on aarch64 with MTE enabled. Cc: Will Deacon <w...@kernel.org> Signed-off-by: Vincenzo Frascino <vincenzo.frasc...@arm.com> Signed-off-by: Catalin Marinas <catalin.mari...@arm.com> Co-developed-by: Peter Collingbourne <p...@google.com> Signed-off-by: Peter Collingbourne <p...@google.com> Reviewed-by: Andrey Konovalov <andreyk...@gmail.com> Link: https://linux-review.googlesource.com/id/If88e396b9e7c058c1a4b5a252274120e77b1898a --- v5: - add test for unreadable first byte of strscpy() source v4: - clarify commit message - improve comment v3: - simplify test case v2: - rebased - fixed test failure mm/kasan/kasan_test_c.c | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c index 59d673400085f..e8d33af634b03 100644 --- a/mm/kasan/kasan_test_c.c +++ b/mm/kasan/kasan_test_c.c @@ -1570,6 +1570,7 @@ static void kasan_memcmp(struct kunit *test) static void kasan_strings(struct kunit *test) { char *ptr; + char *src; size_t size = 24; /* @@ -1581,6 +1582,25 @@ static void kasan_strings(struct kunit *test) ptr = kmalloc(size, GFP_KERNEL | __GFP_ZERO); KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr); + src = kmalloc(KASAN_GRANULE_SIZE, GFP_KERNEL | __GFP_ZERO); + strscpy(src, "f0cacc1a0000000", KASAN_GRANULE_SIZE); + + /* + * Make sure that strscpy() does not trigger KASAN if it overreads into + * poisoned memory. + * + * 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, KASAN_GRANULE_SIZE)); + + /* strscpy should fail if the first byte is unreadable. */ + KUNIT_EXPECT_KASAN_FAIL(test, strscpy(ptr, src + KASAN_GRANULE_SIZE, + KASAN_GRANULE_SIZE)); + + kfree(src); kfree(ptr); /* -- 2.49.0.472.ge94155a9ec-goog
