From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com ([217.140.101.70]:40994 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752005AbdIAQQS (ORCPT ); Fri, 1 Sep 2017 12:16:18 -0400 Date: Fri, 1 Sep 2017 17:16:15 +0100 From: Dave Martin To: Greg KH Cc: Will Deacon , linux-arm-kernel@lists.infradead.org, stable@vger.kernel.org, Ard Biesheuvel Subject: Re: [PATCH] arm64: fpsimd: Prevent registers leaking across exec Message-ID: <20170901161611.GE6321@e103592.cambridge.arm.com> References: <1504025374-17068-1-git-send-email-Dave.Martin@arm.com> <20170831060201.GA7325@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170831060201.GA7325@kroah.com> Sender: stable-owner@vger.kernel.org List-ID: On Thu, Aug 31, 2017 at 08:02:01AM +0200, Greg KH wrote: > On Tue, Aug 29, 2017 at 05:49:34PM +0100, Dave Martin wrote: > > commit 096622104e14d8a1db4860bd557717067a0515d2 upstream. > > > > There are some tricky dependencies between the different stages of > > flushing the FPSIMD register state during exec, and these can race > > with context switch in ways that can cause the old task's regs to > > leak across. In particular, a context switch during the memset() can > > cause some of the task's old FPSIMD registers to reappear. > > > > Disabling preemption for this small window would be no big deal for > > performance: preemption is already disabled for similar scenarios > > like updating the FPSIMD registers in sigreturn. > > > > So, instead of rearranging things in ways that might swap existing > > subtle bugs for new ones, this patch just disables preemption > > around the FPSIMD state flushing so that races of this type can't > > occur here. This brings fpsimd_flush_thread() into line with other > > code paths. > > > > Cc: # 3.16.x > > Cc: # 4.1.x-4.9.x > > Fixes: 674c242c9323 ("arm64: flush FP/SIMD state correctly after execve()") > > Reviewed-by: Ard Biesheuvel > > Signed-off-by: Dave Martin > > Signed-off-by: Will Deacon > > --- > > > > For stable only. > > > > 3.17.x-4.0.x don't appear active, and this patch isn't sufficient to fix > > them (they would need 674c242c9323 also). > > 3.18 is "semi-active" in that I'm trying to keep it alive for the > millions of devices that rely on it out in the world at the moment... Fair enough, I'll bear that in mind for future fixes. Any ideas how long it's likely to linger for? > So I've queued up both of these patches for that tree, don't know why Thanks. > 3.18 didn't catch it in the first place. The commit referenced by the Fixes tag already wasn't in 3.18.x, though that doesn't answer why that patch wasn't picked to 3.18.x in the first place. Dunno. Cheers ---Dave From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave.Martin@arm.com (Dave Martin) Date: Fri, 1 Sep 2017 17:16:15 +0100 Subject: [PATCH] arm64: fpsimd: Prevent registers leaking across exec In-Reply-To: <20170831060201.GA7325@kroah.com> References: <1504025374-17068-1-git-send-email-Dave.Martin@arm.com> <20170831060201.GA7325@kroah.com> Message-ID: <20170901161611.GE6321@e103592.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, Aug 31, 2017 at 08:02:01AM +0200, Greg KH wrote: > On Tue, Aug 29, 2017 at 05:49:34PM +0100, Dave Martin wrote: > > commit 096622104e14d8a1db4860bd557717067a0515d2 upstream. > > > > There are some tricky dependencies between the different stages of > > flushing the FPSIMD register state during exec, and these can race > > with context switch in ways that can cause the old task's regs to > > leak across. In particular, a context switch during the memset() can > > cause some of the task's old FPSIMD registers to reappear. > > > > Disabling preemption for this small window would be no big deal for > > performance: preemption is already disabled for similar scenarios > > like updating the FPSIMD registers in sigreturn. > > > > So, instead of rearranging things in ways that might swap existing > > subtle bugs for new ones, this patch just disables preemption > > around the FPSIMD state flushing so that races of this type can't > > occur here. This brings fpsimd_flush_thread() into line with other > > code paths. > > > > Cc: # 3.16.x > > Cc: # 4.1.x-4.9.x > > Fixes: 674c242c9323 ("arm64: flush FP/SIMD state correctly after execve()") > > Reviewed-by: Ard Biesheuvel > > Signed-off-by: Dave Martin > > Signed-off-by: Will Deacon > > --- > > > > For stable only. > > > > 3.17.x-4.0.x don't appear active, and this patch isn't sufficient to fix > > them (they would need 674c242c9323 also). > > 3.18 is "semi-active" in that I'm trying to keep it alive for the > millions of devices that rely on it out in the world at the moment... Fair enough, I'll bear that in mind for future fixes. Any ideas how long it's likely to linger for? > So I've queued up both of these patches for that tree, don't know why Thanks. > 3.18 didn't catch it in the first place. The commit referenced by the Fixes tag already wasn't in 3.18.x, though that doesn't answer why that patch wasn't picked to 3.18.x in the first place. Dunno. Cheers ---Dave