linux-kernel - Re: [PATCH Bugfix v2 2/4] x86/xsaves: Define and use user_xstate

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Message-ID: <553964D1.300@intel.com>
Date:	Thu, 23 Apr 2015 14:32:01 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	"Yu, Fenghua" <fenghua.yu@...el.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Mallick, Asit K" <asit.k.mallick@...el.com>,
	"Williamson, Glenn P" <glenn.p.williamson@...el.com>
CC:	linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH Bugfix v2 2/4] x86/xsaves: Define and use user_xstate_size
 for xstate size in signal context

On 04/23/2015 10:09 AM, Yu, Fenghua wrote:
>> > If those untouched fields of the xsave buffer are in the "init state", then
>> > we've got no problem.  But, are those "untouched since (1)" fields in the
>> > kernel xsave buf *GUARANTEED* to be in the init state?
> In fact, those untouched fields in kernel xsave buf "IS GUARANTEED" to be in
> the init state.
> 
> Please check __sanitize_i387_state() called just before copy_to_user_xstate().
> That functions GUARANTEES the untouched fields in kernel xsave buf to be in
> init state.

OK, that makes sense.  Other than the horribly-named
sanitize_i387_state(). :)
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