linux-kernel - Re: pt_regs leak into userspace (was Re: [PATCH v3 20/71] ARC: Signal handling)

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Message-ID: <5118C7B6.6040807@imgtec.com>
Date:	Mon, 11 Feb 2013 10:28:06 +0000
From:	James Hogan <james.hogan@...tec.com>
To:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
CC:	Jonas Bonn <jonas.bonn@...il.com>, Arnd Bergmann <arnd@...db.de>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: pt_regs leak into userspace (was Re: [PATCH v3 20/71] ARC: Signal
 handling)

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 <Vineet.Gupta1@...opsys.com> 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.

Cheers
James

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