[v2] x86: Fix bug in strncmp-evex and strncmp-avx2 [BZ #28895]
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| dj/TryBot-apply_patch |
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Patch applied to master at the time it was sent
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| dj/TryBot-32bit |
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Build for i686
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Commit Message
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.
---
string/test-strncmp.c | 22 ++++++++++++++++++++++
sysdeps/x86_64/multiarch/strcmp-avx2.S | 1 +
sysdeps/x86_64/multiarch/strcmp-evex.S | 1 +
3 files changed, 24 insertions(+)
Comments
On Tue, Feb 15, 2022 at 8:42 AM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> 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.
> ---
> string/test-strncmp.c | 22 ++++++++++++++++++++++
> sysdeps/x86_64/multiarch/strcmp-avx2.S | 1 +
> sysdeps/x86_64/multiarch/strcmp-evex.S | 1 +
> 3 files changed, 24 insertions(+)
>
> diff --git a/string/test-strncmp.c b/string/test-strncmp.c
> index 831cb77893..090b61316c 100644
> --- a/string/test-strncmp.c
> +++ b/string/test-strncmp.c
> @@ -423,6 +423,27 @@ check3 (void)
> }
> }
>
> +static void
> +check4 (void)
> +{
> + /* 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;
> + CHAR *s1 = (CHAR *)(buf1 + (getpagesize () & 0xffa) / sizeof (CHAR));
> + CHAR *s2 = (CHAR *)(buf2 + (getpagesize () & 0xfed) / sizeof (CHAR));
> + 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, exp_result);
> +}
> +
> static void
> check_overflow (void)
> {
> @@ -546,6 +567,7 @@ test_main (void)
> check1 ();
> check2 ();
> check3 ();
> + check4 ();
>
> printf ("%23s", "");
> FOR_EACH_IMPL (impl, 0)
> diff --git a/sysdeps/x86_64/multiarch/strcmp-avx2.S b/sysdeps/x86_64/multiarch/strcmp-avx2.S
> index 99e5349be8..07a5a2c889 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 6f42e3155a..56d8c118e4 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
> --
> 2.25.1
>
LGTM.
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
Thanks.
@@ -423,6 +423,27 @@ check3 (void)
}
}
+static void
+check4 (void)
+{
+ /* 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;
+ CHAR *s1 = (CHAR *)(buf1 + (getpagesize () & 0xffa) / sizeof (CHAR));
+ CHAR *s2 = (CHAR *)(buf2 + (getpagesize () & 0xfed) / sizeof (CHAR));
+ 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, exp_result);
+}
+
static void
check_overflow (void)
{
@@ -546,6 +567,7 @@ test_main (void)
check1 ();
check2 ();
check3 ();
+ check4 ();
printf ("%23s", "");
FOR_EACH_IMPL (impl, 0)
@@ -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
@@ -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