From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757510AbcBSKu1 (ORCPT ); Fri, 19 Feb 2016 05:50:27 -0500 Received: from foss.arm.com ([217.140.101.70]:45240 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750712AbcBSKuZ (ORCPT ); Fri, 19 Feb 2016 05:50:25 -0500 Date: Fri, 19 Feb 2016 10:52:29 +0000 From: Lorenzo Pieralisi To: Catalin Marinas Cc: Will Deacon , Mark Rutland , Ard Biesheuvel , linux-kernel@vger.kernel.org, tglx@linutronix.de, Andrey Ryabinin , akpm@linux-foundation.org, hpa@linux.intel.com, mingo@kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] arm64: kasan: clear stale stack poison Message-ID: <20160219105229.GA18597@red-moon> References: <1455816458-19485-1-git-send-email-mark.rutland@arm.com> <20160218175447.GD2538@e104818-lin.cambridge.arm.com> <20160218180353.GG16883@arm.com> <20160218181356.GF2538@e104818-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160218181356.GF2538@e104818-lin.cambridge.arm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 18, 2016 at 06:13:57PM +0000, Catalin Marinas wrote: > On Thu, Feb 18, 2016 at 06:03:54PM +0000, Will Deacon wrote: > > On Thu, Feb 18, 2016 at 05:54:47PM +0000, Catalin Marinas wrote: > > > On Thu, Feb 18, 2016 at 05:27:38PM +0000, Mark Rutland wrote: > > > > @@ -145,6 +146,7 @@ ENTRY(cpu_resume_mmu) > > > > ENDPROC(cpu_resume_mmu) > > > > .popsection > > > > cpu_resume_after_mmu: > > > > + kasan_unpoison_stack 96 > > > > > > I don't think the 96 here is needed since we populate the stack in > > > assembly (__cpu_suspend_enter) and unwind it again still in assembly > > > (cpu_resume_after_mmu), so no KASAN shadow writes/reads. > > > > > > Otherwise the patch looks fine. > > > > I'd much rather it was written in C -- is there a reason we can't do > > that if we use a separate compilation unit where the compiler will > > honour the fno-sanitize flag? > > A simple, non-sanitised C wrapper around __cpu_suspend_enter() would > probably work. We need to make sure it is static inline when !KASAN to > avoid an unnecessary function call. Or we just move cpu_suspend() to a > different compilation unit, though that's a slightly larger function > which we may want to track under KASAN. Both options are ok with me. There is one more. We pass the "saved" sp to __cpu_suspend_save (ie in cpu_suspend_ctx), you can stash it and use it in the resume path (through logical cpu indexing) to carry out the kasan clean-up, in C, with no wrapper needed. With James' hibernate patches: http://lists.infradead.org/pipermail/linux-arm-kernel/2016-February/408597.html this is going to be even easier, since the struct above is on the cpu_suspend stack upon cpu_resume, so you can use the sp in there straight away. We can put together a fix following Catalin's suggestion and when James' patches land in mainline we will update the code. Thanks, Lorenzo