linux-kernel - Re: [PATCH 3.14 79/84] x86/nmi/64: Switch stacks on userspace NMI entry

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Date:	Tue, 29 Sep 2015 19:57:10 +0200
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	stable <stable@...r.kernel.org>,
	Andy Lutomirski <luto@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Borislav Petkov <bp@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 3.14 79/84] x86/nmi/64: Switch stacks on userspace NMI
 entry

On Tue, Sep 29, 2015 at 10:25:52AM -0700, Andy Lutomirski wrote:
> On Tue, Sep 29, 2015 at 8:19 AM, Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
> > 3.14-stable review patch.  If anyone has any objections, please let me know.
> >
> > ------------------
> >
> > From: Andy Lutomirski <luto@...nel.org>
> >
> > commit 9b6e6a8334d56354853f9c255d1395c2ba570e0a upstream.
> >
> > Returning to userspace is tricky: IRET can fail, and ESPFIX can
> > rearrange the stack prior to IRET.
> 
> Just a heads up: under very strange circumstances (most likely
> requires booting with paravirt-noreplace, which is hopefully only used
> by Sasha), this causes a regression that's fixed by
> 83c133cf11fb0e68a51681447e372489f052d40e.  I'm not 100% sure that the
> regression is observable at all, because the same strange
> configuration may also hit the bug fixed by
> fc57a7c68020dcf954428869eafd934c0ab1536f before the regression can
> trigger.
> 
> Anyway, you've been warned.  I wouldn't worry too much about it, though.

Thanks, that patch is still in my queue for future stable kernels, so it
should trickle down soon.

thanks,

greg k-h
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