linux-kernel - Re: [patch] x64, fpu: fix possible FPU leakage in error conditions

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] [day] [month] [year] [list]

Date:	Sat, 26 Jul 2008 16:37:56 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"stable@...nel.org" <stable@...nel.org>
Subject: Re: [patch] x64, fpu: fix possible FPU leakage in error conditions


* Suresh Siddha <suresh.b.siddha@...el.com> wrote:

> On Thu, Jul 24, 2008 at 03:43:44PM -0700, Linus Torvalds wrote:
> > So how about this patch as a starting point? This is the RightThing(tm) to
> > do regardless, and if it then makes it easier to do some other cleanups,
> > we should do it first. What do you think?
> 
> Linus, Attached is my last attempt for the day. Please review. Thanks.
> ---
> 
> restore_fpu_checking() calls init_fpu() in error conditions. While 
> this is wrong(as our main intention is to clear the fpu state of the 
> thread), this was benign before the commit 
> 92d140e21f1ce8cf99320afbbcad73879128e6dc.
> 
> Post commit 92d140e21f1ce8cf99320afbbcad73879128e6dc, live FPU 
> registers may not belong to this process at this error scenario.
> 
> In the error condition for restore_fpu_checking() (especially during 
> the 64bit signal return), we are doing init_fpu(), which saves the 
> live FPU register state (possibly belonging to some other process 
> context) into the thread struct (through unlazy_fpu() in init_fpu()). 
> This is wrong and can leak the FPU data.
> 
> For the signal handler restore error condition in restore_i387(), 
> clear the fpu state present in the thread struct(before ultimately 
> sending a SIGSEGV for badframe).
> 
> For the paranoid error condition check in math_state_restore(), send a 
> SIGSEGV, if we fail to restore the state.

i've applied your patch to tip/x86/fpu for further testing. I suspect 
once it proves reliable we can merge it into v2.6.27, after -rc1.

	Ingo
--
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/