linux-kernel - Re: [PATCH 1/4] signals/sigaltstack: If SS_AUTODISARM, bypass on_sig

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Date:	Wed, 4 May 2016 08:32:33 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Borislav Petkov <bp@...en8.de>, Stas Sergeev <stsp@...t.ru>,
	Al Viro <viro@...iv.linux.org.uk>,
	Aleksa Sarai <cyphar@...har.com>,
	Amanieu d'Antras <amanieu@...il.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Brian Gerst <brgerst@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Heinrich Schuchardt <xypron.glpk@....de>,
	Jason Low <jason.low2@...com>,
	Josh Triplett <josh@...htriplett.org>,
	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Paul Moore <pmoore@...hat.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Richard Weinberger <richard@....at>,
	Sasha Levin <sasha.levin@...cle.com>,
	Shuah Khan <shuahkh@....samsung.com>,
	Tejun Heo <tj@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vladimir Davydov <vdavydov@...allels.com>,
	linux-api@...r.kernel.org
Subject: Re: [PATCH 1/4] signals/sigaltstack: If SS_AUTODISARM, bypass
 on_sig_stack


* Andy Lutomirski <luto@...nel.org> wrote:

> If a signal stack is set up with SS_AUTODISARM, then the kernel
> inherently avoids incorrectly resetting the signal stack if signals
> recurse: the signal stack will be reset on the first signal
> delivery.  This means that we don't need check the stack pointer
> when delivering signals if SS_AUTODISARM is set.
> 
> This will make segmented x86 programs more robust: currently there's
> a hole that could be triggered if ESP/RSP appears to point to the
> signal stack but actually doesn't due to a nonzero SS base.
> 
> Signed-off-by: Stas Sergeev <stsp@...t.ru>

Presuably that SOB from Stas is stray, as there's no matching From: line?
I've removed it.

Thanks,

	Ingo