linux-kernel - [PATCH] [182/223] ARM: 6489/1: thumb2: fix incorrect optimisation in usracc

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Date:	Mon, 13 Dec 2010 00:48:07 +0100 (CET)
From:	Andi Kleen <andi@...stfloor.org>
To:	will.deacon@....com, catalin.marinas@....com,
	rmk+kernel@....linux.org.uk, gregkh@...e.de, ak@...ux.intel.com,
	linux-kernel@...r.kernel.org, stable@...nel.org
Subject: [PATCH] [182/223] ARM: 6489/1: thumb2: fix incorrect optimisation in usracc

2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Will Deacon <will.deacon@....com>

commit 1142b71d85894dcff1466dd6c871ea3c89e0352c upstream.

Commit 8b592783 added a Thumb-2 variant of usracc which, when it is
called with \rept=2, calls usraccoff once with an offset of 0 and
secondly with a hard-coded offset of 4 in order to avoid incrementing
the pointer again. If \inc != 4 then we will store the data to the wrong
offset from \ptr. Luckily, the only caller that passes \rept=2 to this
function is __clear_user so we haven't been actively corrupting user data.

This patch fixes usracc to pass \inc instead of #4 to usraccoff
when it is called a second time.

Reported-by: Tony Thompson <tony.thompson@....com>
Acked-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Russell King <rmk+kernel@....linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
Signed-off-by: Andi Kleen <ak@...ux.intel.com>

---
 arch/arm/include/asm/assembler.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux/arch/arm/include/asm/assembler.h
===================================================================
--- linux.orig/arch/arm/include/asm/assembler.h
+++ linux/arch/arm/include/asm/assembler.h
@@ -215,7 +215,7 @@
 	@ Slightly optimised to avoid incrementing the pointer twice
 	usraccoff \instr, \reg, \ptr, \inc, 0, \cond, \abort
 	.if	\rept == 2
-	usraccoff \instr, \reg, \ptr, \inc, 4, \cond, \abort
+	usraccoff \instr, \reg, \ptr, \inc, \inc, \cond, \abort
 	.endif
 
 	add\cond \ptr, #\rept * \inc
--
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