From: "Yu, Fenghua" <fenghua.yu@intel.com>
To: "Hansen, Dave" <dave.hansen@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
Date: Thu, 23 Apr 2015 17:09:27 +0000 [thread overview]
Message-ID: <3E5A0FA7E9CA944F9D5414FEC6C712205C8D0B81@ORSMSX106.amr.corp.intel.com> (raw)
In-Reply-To: <55383E17.4010408@intel.com>
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> From: Hansen, Dave
> Sent: Wednesday, April 22, 2015 5:35 PM
> On 04/22/2015 05:06 PM, Yu, Fenghua wrote:
> > We need to copy ALL of supported xstates to user. Using xstate_bv only
> > copies partial xstates that are in non-init status.
> >
> > Xstate_bv only has xstates that are in non-init status. The xstates
> > that are in init status will not be copied to user if using xstate_bv.
> > In this case, the xstates that are in init status will be all zeros in
> > the user buffer (remember we clear the user buffer before). That's
> incorrect.
> I'm not convinced. Let's step through this.
>
> 1. kernel does an xsaves
> 2. Due to the 'init optimization' xstate_bv != pcntxt_mask, and some
> fields of kernel xsave buffer are untouched 3. Kernel looks at pcntxt_mask,
> which means it copies untouched xsave
> buffer fields out to userspace
>
> 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.
Thanks.
-Fenghua
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next prev parent reply other threads:[~2015-04-23 17:09 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-22 4:51 [PATCH Bugfix v2 0/4] x86/xsave/xsaves: Fix a few xsave/xsaves related bugs Fenghua Yu
2015-04-22 4:51 ` [PATCH Bugfix v2 1/4] x86/xsave.c: Fix xstate offsets and sizes enumeration Fenghua Yu
2015-04-22 4:51 ` [PATCH Bugfix v2 2/4] x86/xsaves: Define and use user_xstate_size for xstate size in signal context Fenghua Yu
2015-04-22 18:45 ` Dave Hansen
2015-04-22 19:05 ` Yu, Fenghua
2015-04-22 19:34 ` Dave Hansen
2015-04-23 0:06 ` Yu, Fenghua
2015-04-23 0:21 ` Dave Hansen
2015-04-23 0:23 ` Yu, Fenghua
2015-04-23 0:34 ` Dave Hansen
2015-04-23 17:09 ` Yu, Fenghua [this message]
2015-04-23 21:32 ` Dave Hansen
2015-04-28 14:28 ` Dave Hansen
2015-04-28 22:09 ` Dave Hansen
2015-04-28 22:11 ` Yu, Fenghua
2015-04-29 13:53 ` Dave Hansen
2015-04-22 4:51 ` [PATCH Bugfix v2 3/4] x86/xsaves: Rename xstate_size to kernel_xstate_size to explicitly distinguish xstate size in kernel from user space Fenghua Yu
2015-04-22 4:51 ` [PATCH Bugfix v2 4/4] x86/xsave: Don't add new states in xsave_struct Fenghua Yu
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