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

From: Andy Lutomirski
Date: Tue Sep 29 2015 - 13:26:29 EST

On Tue, Sep 29, 2015 at 8:19 AM, Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> 3.14-stable review patch. If anyone has any objections, please let me know.
> ------------------
> From: Andy Lutomirski <luto@xxxxxxxxxx>
> 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

Anyway, you've been warned. I wouldn't worry too much about it, though.

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