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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CACM3HyG+4Pzx02iL9atxG+FOLiCcTeXR+ivzRO78bqDHNp5rGQ@mail.gmail.com>
Date:	Mon, 11 Feb 2013 11:53:52 +0100
From:	Jonas Bonn <jonas.bonn@...il.com>
To:	James Hogan <james.hogan@...tec.com>
Cc:	Vineet Gupta <Vineet.Gupta1@...opsys.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 February 2013 11:28, James Hogan <james.hogan@...tec.com> 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 <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.

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.

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.

/Jonas
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/