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| author |   Noah Goldstein <goldstein.w.n@gmail.com> | 2022-02-15 20:27:21 -0600 |
|---|---|---|
| committer |   Andreas K. Hüttel <dilfridge@gentoo.org> | 2022-05-14 23:20:00 +0200 |
| commit | 91ca927bb0c3a158130d491fd07fb5c157deb68e (patch) | |
| tree | 72763ec7acb4153e50af250d88eb9e69ba29a4c6 | |
| parent | x86: Set .text section in memset-vec-unaligned-erms (diff) | |
| download | glibc-91ca927bb0c3a158130d491fd07fb5c157deb68e.tar.gz glibc-91ca927bb0c3a158130d491fd07fb5c157deb68e.tar.bz2 glibc-91ca927bb0c3a158130d491fd07fb5c157deb68e.zip | |
x86: Fix bug in strncmp-evex and strncmp-avx2 [BZ #28895]
Logic can read before the start of `s1` / `s2` if both `s1` and `s2`
are near the start of a page. To avoid having the result contimated by
these comparisons the `strcmp` variants would mask off these
comparisons. This was missing in the `strncmp` variants causing
the bug. This commit adds the masking to `strncmp` so that out of
range comparisons don't affect the result.
test-strcmp, test-strncmp, test-wcscmp, and test-wcsncmp all pass as
well a full xcheck on x86_64 linux.
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
(cherry picked from commit e108c02a5e23c8c88ce66d8705d4a24bb6b9a8bf)
(cherry picked from commit 5373c90f2ea3c3fa9931a684c9b81c648dfbe8d7)
| -rw-r--r-- | string/test-strncmp.c | 20 | ||||
| -rw-r--r-- | sysdeps/x86_64/multiarch/strcmp-avx2.S | 1 | ||||
| -rw-r--r-- | sysdeps/x86_64/multiarch/strcmp-evex.S | 1 |
3 files changed, 17 insertions, 5 deletions
diff --git a/string/test-strncmp.c b/string/test-strncmp.c index 97e831d88f..56e23670ae 100644 --- a/string/test-strncmp.c +++ b/string/test-strncmp.c @@ -438,13 +438,23 @@ check3 (void) static void check4 (void) { - const CHAR *s1 = L ("abc"); - CHAR *s2 = STRDUP (s1); + /* To trigger bug 28895; We need 1) both s1 and s2 to be within 32 bytes of + the end of the page. 2) For there to be no mismatch/null byte before the + first page cross. 3) For length (`n`) to be large enough for one string to + cross the page. And 4) for there to be either mismatch/null bytes before + the start of the strings. */ + + size_t size = 10; + size_t addr_mask = (getpagesize () - 1) ^ (sizeof (CHAR) - 1); + CHAR *s1 = (CHAR *)(buf1 + (addr_mask & 0xffa)); + CHAR *s2 = (CHAR *)(buf2 + (addr_mask & 0xfed)); + int exp_result; + STRCPY (s1, L ("tst-tlsmod%")); + STRCPY (s2, L ("tst-tls-manydynamic73mod")); + exp_result = SIMPLE_STRNCMP (s1, s2, size); FOR_EACH_IMPL (impl, 0) - check_result (impl, s1, s2, SIZE_MAX, 0); - - free (s2); + check_result (impl, s1, s2, size, exp_result); } int diff --git a/sysdeps/x86_64/multiarch/strcmp-avx2.S b/sysdeps/x86_64/multiarch/strcmp-avx2.S index cdded412a7..f9bdc5ccd0 100644 --- a/sysdeps/x86_64/multiarch/strcmp-avx2.S +++ b/sysdeps/x86_64/multiarch/strcmp-avx2.S @@ -661,6 +661,7 @@ L(ret8): # ifdef USE_AS_STRNCMP .p2align 4,, 10 L(return_page_cross_end_check): + andl %r10d, %ecx tzcntl %ecx, %ecx leal -VEC_SIZE(%rax, %rcx), %ecx cmpl %ecx, %edx diff --git a/sysdeps/x86_64/multiarch/strcmp-evex.S b/sysdeps/x86_64/multiarch/strcmp-evex.S index ed56af8ecd..0dfa62bd14 100644 --- a/sysdeps/x86_64/multiarch/strcmp-evex.S +++ b/sysdeps/x86_64/multiarch/strcmp-evex.S @@ -689,6 +689,7 @@ L(ret8): # ifdef USE_AS_STRNCMP .p2align 4,, 10 L(return_page_cross_end_check): + andl %r10d, %ecx tzcntl %ecx, %ecx leal -VEC_SIZE(%rax, %rcx, SIZE_OF_CHAR), %ecx # ifdef USE_AS_WCSCMP |