91 lines
3.0 KiB
Diff
91 lines
3.0 KiB
Diff
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From e108c02a5e23c8c88ce66d8705d4a24bb6b9a8bf Mon Sep 17 00:00:00 2001
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From: Noah Goldstein <goldstein.w.n@gmail.com>
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Date: Tue, 15 Feb 2022 20:27:21 -0600
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Subject: [PATCH] x86: Fix bug in strncmp-evex and strncmp-avx2 [BZ #28895]
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Content-type: text/plain; charset=UTF-8
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Logic can read before the start of `s1` / `s2` if both `s1` and `s2`
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are near the start of a page. To avoid having the result contimated by
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these comparisons the `strcmp` variants would mask off these
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comparisons. This was missing in the `strncmp` variants causing
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the bug. This commit adds the masking to `strncmp` so that out of
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range comparisons don't affect the result.
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test-strcmp, test-strncmp, test-wcscmp, and test-wcsncmp all pass as
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well a full xcheck on x86_64 linux.
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Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
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---
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string/test-strncmp.c | 23 +++++++++++++++++++++++
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sysdeps/x86_64/multiarch/strcmp-avx2.S | 1 +
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sysdeps/x86_64/multiarch/strcmp-evex.S | 1 +
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3 files changed, 25 insertions(+)
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diff --git a/string/test-strncmp.c b/string/test-strncmp.c
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index 927a6daa..e61fffd9 100644
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--- a/string/test-strncmp.c
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+++ b/string/test-strncmp.c
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@@ -403,6 +403,28 @@ check2 (void)
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free (s2);
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}
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+static void
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+check4 (void)
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+{
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+ /* To trigger bug 28895; We need 1) both s1 and s2 to be within 32 bytes of
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+ the end of the page. 2) For there to be no mismatch/null byte before the
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+ first page cross. 3) For length (`n`) to be large enough for one string to
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+ cross the page. And 4) for there to be either mismatch/null bytes before
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+ the start of the strings. */
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+
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+ size_t size = 10;
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+ size_t addr_mask = (getpagesize () - 1) ^ (sizeof (CHAR) - 1);
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+ CHAR *s1 = (CHAR *)(buf1 + (addr_mask & 0xffa));
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+ CHAR *s2 = (CHAR *)(buf2 + (addr_mask & 0xfed));
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+ int exp_result;
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+
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+ STRCPY (s1, L ("tst-tlsmod%"));
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+ STRCPY (s2, L ("tst-tls-manydynamic73mod"));
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+ exp_result = SIMPLE_STRNCMP (s1, s2, size);
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+ FOR_EACH_IMPL (impl, 0)
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+ check_result (impl, s1, s2, size, exp_result);
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+}
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+
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static void
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check3 (void)
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{
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@@ -445,6 +467,7 @@ test_main (void)
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check1 ();
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check2 ();
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check3 ();
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+ check4 ();
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printf ("%23s", "");
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FOR_EACH_IMPL (impl, 0)
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diff --git a/sysdeps/x86_64/multiarch/strcmp-avx2.S b/sysdeps/x86_64/multiarch/strcmp-avx2.S
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index 04675aa4..179cc0e3 100644
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--- a/sysdeps/x86_64/multiarch/strcmp-avx2.S
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+++ b/sysdeps/x86_64/multiarch/strcmp-avx2.S
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@@ -661,6 +661,7 @@ L(ret8):
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# ifdef USE_AS_STRNCMP
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.p2align 4,, 10
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L(return_page_cross_end_check):
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+ andl %r10d, %ecx
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tzcntl %ecx, %ecx
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leal -VEC_SIZE(%rax, %rcx), %ecx
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cmpl %ecx, %edx
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diff --git a/sysdeps/x86_64/multiarch/strcmp-evex.S b/sysdeps/x86_64/multiarch/strcmp-evex.S
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index ed56af8e..0dfa62bd 100644
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--- a/sysdeps/x86_64/multiarch/strcmp-evex.S
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+++ b/sysdeps/x86_64/multiarch/strcmp-evex.S
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@@ -689,6 +689,7 @@ L(ret8):
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# ifdef USE_AS_STRNCMP
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.p2align 4,, 10
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L(return_page_cross_end_check):
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+ andl %r10d, %ecx
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tzcntl %ecx, %ecx
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leal -VEC_SIZE(%rax, %rcx, SIZE_OF_CHAR), %ecx
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# ifdef USE_AS_WCSCMP
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--
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GitLab
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