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

[Andy Lutomirski]

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
trigger.

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

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