Commit 62d32440 authored by Vincenzo Frascino's avatar Vincenzo Frascino Committed by Kees Cook
Browse files

kasan: Add strscpy() test to trigger tag fault on arm64 



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 <will@kernel.org>
Signed-off-by: default avatarVincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Co-developed-by: default avatarPeter Collingbourne <pcc@google.com>
Signed-off-by: default avatarPeter Collingbourne <pcc@google.com>
Reviewed-by: default avatarAndrey Konovalov <andreyknvl@gmail.com>
Link: https://linux-review.googlesource.com/id/If88e396b9e7c058c1a4b5a252274120e77b1898a


Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20250403000703.2584581-3-pcc@google.com


Signed-off-by: default avatarKees Cook <kees@kernel.org>
parent d94c12bd

mm/kasan/kasan_test_c.c

+20 −0
Original line number Diff line number Diff line
@@ -1567,6 +1567,7 @@ static void kasan_memcmp(struct kunit *test) 
static void kasan_strings(struct kunit *test)

{

	char *ptr;

	char *src;

	size_t size = 24;



	/*
@@ -1578,6 +1579,25 @@ 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);



	/*