linux-kernel - Re: Sanitize CPU-state when switching tasks (was sanitize CPU-state when switching from virtual-8086 mode to other task)

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Message-ID: <CA+55aFxQnY_PCG_n4=0w-VG=YLXL-yr7oMxyy0WU2gCBAf3ydg@mail.gmail.com>
Date:	Fri, 10 Jan 2014 08:42:33 +0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	"H. Peter Anvin" <hpa@...or.com>, halfdog <me@...fdog.net>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ben Hutchings <ben@...adent.org.uk>
Subject: Re: Sanitize CPU-state when switching tasks (was sanitize CPU-state
 when switching from virtual-8086 mode to other task)

On Fri, Jan 10, 2014 at 6:58 AM, Borislav Petkov <bp@...en8.de> wrote:
>
> Ok, I was able to reproduce

Looking at this, I think this is just a bug in our
restore_fpu_checking() hackery for X86_FEATURE_FXSAVE_LEAK..

Which also explains why it only triggers on E-350 - it's only relevant
for those K7/K8 CPU's that use this.

Maybe just add a fcnlex to before the emms? Something like this
(TOTALLY UNTESTED!!) attached patch.

                 Linus

View attachment "patch.diff" of type "text/plain" (1070 bytes)