diff mbox

Fix i686 memchr for large input sizes

Message ID 1483367199-20720-1-git-send-email-adhemerval.zanella@linaro.org
State New
Headers show

Commit Message

Adhemerval Zanella Netto Jan. 2, 2017, 2:26 p.m. UTC 
Similar to BZ#19387 and BZ#20971, both i686 memchr optimized assembly
implementations (memchr-sse2-bsf and memchr-sse2) do not handle the
size overflow correctly.

It is shown by the new tests added by commit 3daef2c8ee4df29, where
both implementation fails with size as SIZE_MAX.

This patch uses a similar strategy used on 3daef2c8ee4df2, where
saturared math is used for overflow case.

Checked on i686-linux-gnu.

	[BZ #21014]
	* sysdeps/i386/i686/multiarch/memchr-sse2-bsf.S (MEMCHR): Avoid overflow
	in pointer addition.
	* sysdeps/i386/i686/multiarch/memchr-sse2.S (MEMCHR): Likewise.
---
 ChangeLog                                     |  7 +++++++
 sysdeps/i386/i686/multiarch/memchr-sse2-bsf.S | 10 ++++++++--
 sysdeps/i386/i686/multiarch/memchr-sse2.S     |  8 +++++++-
 3 files changed, 22 insertions(+), 3 deletions(-)

Comments

Siddhesh Poyarekar Jan. 2, 2017, 7:03 p.m. UTC | #1 
On Monday 02 January 2017 07:56 PM, Adhemerval Zanella wrote:
> Similar to BZ#19387 and BZ#20971, both i686 memchr optimized assembly
> implementations (memchr-sse2-bsf and memchr-sse2) do not handle the
> size overflow correctly.
> 
> It is shown by the new tests added by commit 3daef2c8ee4df29, where
> both implementation fails with size as SIZE_MAX.
> 
> This patch uses a similar strategy used on 3daef2c8ee4df2, where
> saturared math is used for overflow case.
> 
> Checked on i686-linux-gnu.
> 
> 	[BZ #21014]
> 	* sysdeps/i386/i686/multiarch/memchr-sse2-bsf.S (MEMCHR): Avoid overflow
> 	in pointer addition.
> 	* sysdeps/i386/i686/multiarch/memchr-sse2.S (MEMCHR): Likewise.

Looks good to me.

Siddhesh
diff mbox

Patch

diff --git a/sysdeps/i386/i686/multiarch/memchr-sse2-bsf.S b/sysdeps/i386/i686/multiarch/memchr-sse2-bsf.S
index c035329..dd31648 100644
--- a/sysdeps/i386/i686/multiarch/memchr-sse2-bsf.S
+++ b/sysdeps/i386/i686/multiarch/memchr-sse2-bsf.S
@@ -149,9 +149,15 @@  L(crosscache):
 	.p2align 4
 L(unaligned_no_match):
 # ifndef USE_AS_RAWMEMCHR
-	sub	$16, %edx
+        /* Calculate the last acceptable address and check for possible
+           addition overflow by using satured math:
+           edx = ecx + edx
+           edx |= -(edx < ecx)  */
 	add	%ecx, %edx
-	jle	L(return_null)
+	sbb	%eax, %eax
+	or	%eax, %edx
+	sub	$16, %edx
+	jbe	L(return_null)
 	add	$16, %edi
 # else
 	add	$16, %edx
diff --git a/sysdeps/i386/i686/multiarch/memchr-sse2.S b/sysdeps/i386/i686/multiarch/memchr-sse2.S
index f1a11b5..910679c 100644
--- a/sysdeps/i386/i686/multiarch/memchr-sse2.S
+++ b/sysdeps/i386/i686/multiarch/memchr-sse2.S
@@ -118,8 +118,14 @@  L(crosscache):
 # ifndef USE_AS_RAWMEMCHR
 	jnz	L(match_case2_prolog1)
 	lea	-16(%edx), %edx
+        /* Calculate the last acceptable address and check for possible
+           addition overflow by using satured math:
+           edx = ecx + edx
+           edx |= -(edx < ecx)  */
 	add	%ecx, %edx
-	jle	L(return_null)
+	sbb	%eax, %eax
+	or	%eax, %edx
+	jbe	L(return_null)
 	lea	16(%edi), %edi
 # else
 	jnz	L(match_case1_prolog1)