linux-kernel - Re: [RFC] de-asmify the x86-64 system call slowpath

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Message-ID: <20140127223257.GE10323@ZenIV.linux.org.uk>
Date:	Mon, 27 Jan 2014 22:32:57 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andy Lutomirski <luto@...capital.net>, Peter Anvin <hpa@...or.com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] de-asmify the x86-64 system call slowpath

On Mon, Jan 27, 2014 at 02:17:23PM -0800, Linus Torvalds wrote:
> On Mon, Jan 27, 2014 at 2:06 PM, Andy Lutomirski <luto@...capital.net> wrote:
> >
> > It's not just ip and sp -- cs matters here, too, I think.
> 
> For signal *delivery*, CS will always be __USER_CS, and %rcx can be
> crap, so sysret should be fine. We could easily check that %rip is
> valid in the whole slow-path instead of saying "return 1 if we did
> do_signal()".

do_signal() is also a place where arbitrary changes to regs might've
been done by tracer, so regs->cs might need to be checked in the same
place where we validate regs->rip ;-/
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