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Date: Thu, 23 Apr 2015 14:32:01 -0700
From: Dave Hansen <dave.hansen@intel.com>
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To: "Yu, Fenghua" <fenghua.yu@intel.com>,
        "H. Peter Anvin" <hpa@linux.intel.com>, Ingo Molnar <mingo@elte.hu>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Mallick, Asit K" <asit.k.mallick@intel.com>,
        "Williamson, Glenn P" <glenn.p.williamson@intel.com>
CC: linux-kernel <linux-kernel@vger.kernel.org>, x86 <x86@kernel.org>
Subject: Re: [PATCH Bugfix v2 2/4] x86/xsaves: Define and use user_xstate_size
 for xstate size in signal context
References: <1429678319-61356-1-git-send-email-fenghua.yu@intel.com> <1429678319-61356-3-git-send-email-fenghua.yu@intel.com> <5537EC31.7080808@intel.com> <3E5A0FA7E9CA944F9D5414FEC6C712205C8CE779@ORSMSX106.amr.corp.intel.com> <5537F7AA.3010609@intel.com> <3E5A0FA7E9CA944F9D5414FEC6C712205C8CF9CF@ORSMSX106.amr.corp.intel.com> <55383E17.4010408@intel.com> <3E5A0FA7E9CA944F9D5414FEC6C712205C8D0B81@ORSMSX106.amr.corp.intel.com>
In-Reply-To: <3E5A0FA7E9CA944F9D5414FEC6C712205C8D0B81@ORSMSX106.amr.corp.intel.com>
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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(). :)