lib/glibc
1
0
Fork 0
mirror of https://sourceware.org/git/glibc.git synced 2025-08-07 06:43:00 +03:00
Code Activity

x86: Fix bug in strncmp-evex and strncmp-avx2 [BZ #28895]

Browse Source 
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 e108c02a5e)
This commit is contained in:
Noah Goldstein
2022-02-15 20:27:21 -06:00
committed by Sunil K Pandey
parent c394d7e11a
commit 676f7bcf11
3 changed files with 17 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

20
string/test-strncmp.c
View File

@@ -437,13 +437,23 @@ 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