Messages in this thread | | | Date | Thu, 14 Oct 2021 19:40:45 -0700 | From | Kees Cook <> | Subject | Re: [PATCH 1/2] kasan: test: use underlying string helpers |
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On October 14, 2021 1:12:54 AM PDT, Vincenzo Frascino <vincenzo.frascino@arm.com> wrote: > > >On 10/13/21 5:00 PM, Arnd Bergmann wrote: >> From: Arnd Bergmann <arnd@arndb.de> >> >> Calling memcmp() and memchr() with an intentional buffer overflow >> is now caught at compile time: >> >> In function 'memcmp', >> inlined from 'kasan_memcmp' at lib/test_kasan.c:897:2: >> include/linux/fortify-string.h:263:25: error: call to '__read_overflow' declared with attribute error: detected read beyond size of object (1st parameter) >> 263 | __read_overflow(); >> | ^~~~~~~~~~~~~~~~~ >> In function 'memchr', >> inlined from 'kasan_memchr' at lib/test_kasan.c:872:2: >> include/linux/fortify-string.h:277:17: error: call to '__read_overflow' declared with attribute error: detected read beyond size of object (1st parameter) >> 277 | __read_overflow(); >> | ^~~~~~~~~~~~~~~~~ >> >> Change the kasan tests to wrap those inside of a noinline function >> to prevent the compiler from noticing the bug and let kasan find >> it at runtime. >> >> Signed-off-by: Arnd Bergmann <arnd@arndb.de> > >Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
How about just explicitly making the size invisible to the compiler?
I did this for similar issues in the same source:
https://lore.kernel.org/linux-hardening/20211006181544.1670992-1-keescook@chromium.org/T/#u
-Kees
> >> --- >> lib/test_kasan.c | 19 +++++++++++++++++-- >> 1 file changed, 17 insertions(+), 2 deletions(-) >> >> diff --git a/lib/test_kasan.c b/lib/test_kasan.c >> index 67ed689a0b1b..903215e944f1 100644 >> --- a/lib/test_kasan.c >> +++ b/lib/test_kasan.c >> @@ -852,6 +852,21 @@ static void kmem_cache_invalid_free(struct kunit *test) >> kmem_cache_destroy(cache); >> } >> >> +/* >> + * noinline wrappers to prevent the compiler from noticing the overflow >> + * at compile time rather than having kasan catch it. >> + * */ >> +static noinline void *__kasan_memchr(const void *s, int c, size_t n) >> +{ >> + return memchr(s, c, n); >> +} >> + >> +static noinline int __kasan_memcmp(const void *s1, const void *s2, size_t n) >> +{ >> + return memcmp(s1, s2, n); >> +} >> + >> + >> static void kasan_memchr(struct kunit *test) >> { >> char *ptr; >> @@ -870,7 +885,7 @@ static void kasan_memchr(struct kunit *test) >> KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr); >> >> KUNIT_EXPECT_KASAN_FAIL(test, >> - kasan_ptr_result = memchr(ptr, '1', size + 1)); >> + kasan_ptr_result = __kasan_memchr(ptr, '1', size + 1)); >> >> kfree(ptr); >> } >> @@ -895,7 +910,7 @@ static void kasan_memcmp(struct kunit *test) >> memset(arr, 0, sizeof(arr)); >> >> KUNIT_EXPECT_KASAN_FAIL(test, >> - kasan_int_result = memcmp(ptr, arr, size+1)); >> + kasan_int_result = __kasan_memcmp(ptr, arr, size+1)); >> kfree(ptr); >> } >> >> >
-- Kees Cook
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