From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Hogan Subject: Re: pt_regs leak into userspace (was Re: [PATCH v3 20/71] ARC: Signal handling) Date: Mon, 11 Feb 2013 10:57:28 +0000 Message-ID: <5118CE98.5040509@imgtec.com> References: <1359024639-21915-1-git-send-email-vgupta@synopsys.com> <1359024639-21915-9-git-send-email-vgupta@synopsys.com> <51189D2F.4030000@synopsys.com> <5118C458.2070205@synopsys.com> <5118C7B6.6040807@imgtec.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: Received: from multi.imgtec.com ([194.200.65.239]:30800 "EHLO multi.imgtec.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753839Ab3BKK5j (ORCPT ); Mon, 11 Feb 2013 05:57:39 -0500 In-Reply-To: Sender: linux-arch-owner@vger.kernel.org List-ID: To: Jonas Bonn Cc: Vineet Gupta , Arnd Bergmann , "linux-arch@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Al Viro On 11/02/13 10:53, Jonas Bonn wrote: > On 11 February 2013 11:28, James Hogan wrote: >> On 11/02/13 10:13, Vineet Gupta wrote: >>> On Monday 11 February 2013 03:06 PM, Jonas Bonn wrote: >>>> On 11 February 2013 08:26, Vineet Gupta wrote: >>>> >>>>> The only downside of this patch is that userspace signal stack grows in size, >>>>> since signal frame only cares about scratch regs (pt_regs), but has to accommodate >>>>> unused placeholder for callee regs too by virtue of using user_regs_struct. >>>> Is this really true? Don't setcontext and friends require that _all_ >>>> the registers be part of sigcontext? >>> >>> But for an ABI - callee saved regs will anyhow be saved/restored even in >>> setcontext case ! So collecting it for that purpose seems useless, or am I missing >>> something here. >> >> I think Jonas' point was that signals are asynchronous, i.e. you could >> get interrupted by a signal at virtually any time during the program's >> execution. > > No, I agree that the callee-saved regs don't need to be saved across a > signal handler invocation. It's really just the setcontext case that > wants to be able to swap out the callee-saved regs. Yes, I was getting muddled, sorry! > And now that I think about it some more, I think this is done > incorrectly in the openrisc arch, too, as the fast-path for > rt_sigreturn probably only restores the call-clobbered regs. > sigreturn probably needs to be special-cased to _always_ restore all > the regs on its way back to userspace. Not for the "signal" case, but > for the "setcontext" case; but these two are pretty-much > indistinguishable. Cheers James