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authorNoah Goldstein <goldstein.w.n@gmail.com>2022-02-15 20:27:21 -0600
committerAndreas K. Hüttel <dilfridge@gentoo.org>2022-05-14 23:20:00 +0200
commit91ca927bb0c3a158130d491fd07fb5c157deb68e (patch)
tree72763ec7acb4153e50af250d88eb9e69ba29a4c6
parentx86: Set .text section in memset-vec-unaligned-erms (diff)
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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.c20
-rw-r--r--sysdeps/x86_64/multiarch/strcmp-avx2.S1
-rw-r--r--sysdeps/x86_64/multiarch/strcmp-evex.S1
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