Subject: [PATCH] ARM: SWP emulation: Restore original *data when failed

From: [email-masked] (Vladimir Murzin)
Date: Fri, 16 Oct 2015 08:52:24 +0100

On 15/10/15 14:25, Vladimir Murzin wrote:
> On 15/10/15 14:02, Will Deacon wrote:
>> On Thu, Oct 15, 2015 at 10:17:47AM +0100, Vladimir Murzin wrote:
>>> We might need the same change for arm64 counterpart (see
>>> arch/arm64/kernel/armv8_deprecated.c).
>>
>> Something like below?
> 
> Looks good. Should these two go to stable?

On the second thought looks like we still update *data in case stxr
fails (or I need more coffee).

Vladimir

> 
> Vladimir
> 
>>
>> Will
>>
>> >From 63c3e83073cfac2e011adf0ed6f335275cc977a7 Mon Sep 17 00:00:00 2001
>> From: Will Deacon <[email-masked]>
>> Date: Thu, 15 Oct 2015 13:55:53 +0100
>> Subject: [PATCH] arm64: compat: fix stxr failure case in SWP emulation
>>
>> If the STXR instruction fails in the SWP emulation code, we leave *data
>> overwritten with the loaded value, therefore corrupting the data written
>> by a subsequent, successful attempt.
>>
>> This patch re-jigs the code so that we only write back to *data once we
>> know that the update has happened.
>>
>> Reported-by: Shengjiu Wang <[email-masked]>
>> Reported-by: Vladimir Murzin <[email-masked]>
>> Signed-off-by: Will Deacon <[email-masked]>
>> ---
>>  arch/arm64/kernel/armv8_deprecated.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/armv8_deprecated.c b/arch/arm64/kernel/armv8_deprecated.c
>> index bcee7abac68e..6039d1eb5912 100644
>> --- a/arch/arm64/kernel/armv8_deprecated.c
>> +++ b/arch/arm64/kernel/armv8_deprecated.c
>> @@ -284,12 +284,12 @@ static void register_insn_emulation_sysctl(struct ctl_table *table)
>>  	__asm__ __volatile__(					\
>>  	ALTERNATIVE("nop", SET_PSTATE_PAN(0), ARM64_HAS_PAN,	\
>>  		    CONFIG_ARM64_PAN)				\
>> -	"	mov		%w2, %w1\n"			\
>> -	"0:	ldxr"B"		%w1, [%3]\n"			\
>> -	"1:	stxr"B"		%w0, %w2, [%3]\n"		\
>> +	"0:	ldxr"B"		%w2, [%3]\n"			\
>> +	"1:	stxr"B"		%w0, %w1, [%3]\n"		\
>>  	"	cbz		%w0, 2f\n"			\
>>  	"	mov		%w0, %w4\n"			\
>>  	"2:\n"							\
>> +	"	mov		%w1, %w2\n"			\
>>  	"	.pushsection	 .fixup,\"ax\"\n"		\
>>  	"	.align		2\n"				\
>>  	"3:	mov		%w0, %w5\n"			\
>>
> 
> 
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