linux-kernel - Re: [PATCH] arm: Remove early stack deallocation from restore_user

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Message-ID: <20150109164608.GV12302@n2100.arm.linux.org.uk>
Date:	Fri, 9 Jan 2015 16:46:08 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Daniel Thompson <daniel.thompson@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	patches@...aro.org, linaro-kernel@...ts.linaro.org,
	John Stultz <john.stultz@...aro.org>,
	Sumit Semwal <sumit.semwal@...aro.org>
Subject: Re: [PATCH] arm: Remove early stack deallocation from
 restore_user_regs

On Mon, Jan 05, 2015 at 03:12:38PM +0000, Daniel Thompson wrote:
> Currently restore_user_regs deallocates the SVC stack early in
> its execution and relies on no exception being taken between
> the deallocation and the registers being restored. The introduction
> of a default FIQ handler that also uses the SVC stack breaks this
> assumption and can result in corrupted register state.
> 
> This patch works around the problem by removing the early
> stack deallocation and using r2 as a temporary instead. I have
> not found a way to do this without introducing an extra mov
> instruction to the macro.
> 
> Signed-off-by: Daniel Thompson <daniel.thompson@...aro.org>
> ---

Please put it in the patch system, thanks.  I think we should queue
this one for stable too, as I think we need this for v3.18
(as a result of c0e7f7ee717e2b4c5791e7422424c96b5008c39e,
ARM: 8150/3: fiq: Replace default FIQ handler)?

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