[PATCH AUTOSEL 5.16 52/52] kasan: test: fix compatibility with FORTIFY_SOURCE

Sasha Levin
2022-02-03T20:34:17Z

From: Marco Elver <elver@google.com>

[ Upstream commit 09c6304e38e440b93a9ebf3f3cf75cd6cb529f91 ]

With CONFIG_FORTIFY_SOURCE enabled, string functions will also perform
dynamic checks using __builtin_object_size(ptr), which when failed will
panic the kernel.

Because the KASAN test deliberately performs out-of-bounds operations,
the kernel panics with FORTIFY_SOURCE, for example:

| kernel BUG at lib/string_helpers.c:910!
| invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
| CPU: 1 PID: 137 Comm: kunit_try_catch Tainted: G B 5.16.0-rc3+ #3
| Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
| RIP: 0010:fortify_panic+0x19/0x1b
| ...
| Call Trace:
| kmalloc_oob_in_memset.cold+0x16/0x16
| ...

Fix it by also hiding `ptr` from the optimizer, which will ensure that
__builtin_object_size() does not return a valid size, preventing
fortified string functions from panicking.

Link: https://lkml.kernel.org/r/20220124160744.1244685-1-elver@google.com
Signed-off-by: Marco Elver <elver@google.com>
Reported-by: Nico Pache <npache@redhat.com>
Reviewed-by: Nico Pache <npache@redhat.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
lib/test_kasan.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 0643573f86862..2ef2948261bf8 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -492,6 +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(ptr);
OPTIMIZER_HIDE_VAR(size);
KUNIT_EXPECT_KASAN_FAIL(test,
memset(ptr, 0, size + KASAN_GRANULE_SIZE));
@@ -515,6 +516,7 @@ 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(ptr);
OPTIMIZER_HIDE_VAR(invalid_size);
KUNIT_EXPECT_KASAN_FAIL(test,
memmove((char *)ptr, (char *)ptr + 4, invalid_size));
@@ -531,6 +533,7 @@ static void kmalloc_memmove_invalid_size(struct kunit *test)
KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);

memset((char *)ptr, 0, 64);
+ OPTIMIZER_HIDE_VAR(ptr);
KUNIT_EXPECT_KASAN_FAIL(test,
memmove((char *)ptr, (char *)ptr + 4, invalid_size));
kfree(ptr);
@@ -869,6 +872,7 @@ static void kasan_memchr(struct kunit *test)
ptr = kmalloc(size, GFP_KERNEL | __GFP_ZERO);
KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);

+ OPTIMIZER_HIDE_VAR(ptr);
OPTIMIZER_HIDE_VAR(size);
KUNIT_EXPECT_KASAN_FAIL(test,
kasan_ptr_result = memchr(ptr, '1', size + 1));
@@ -895,6 +899,7 @@ static void kasan_memcmp(struct kunit *test)
KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
memset(arr, 0, sizeof(arr));

+ OPTIMIZER_HIDE_VAR(ptr);
OPTIMIZER_HIDE_VAR(size);
KUNIT_EXPECT_KASAN_FAIL(test,
kasan_int_result = memcmp(ptr, arr, size+1));
--
2.34.1