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From: "Wu, Feng" <feng.wu@intel.com>
To: Jan Beulich <jbeulich@suse.com>,
	"andrew.cooper3@citrix.com" <andrew.cooper3@citrix.com>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: "Wu, Feng" <feng.wu@intel.com>, "keir@xen.org" <keir@xen.org>
Subject: Re: [PATCH 2/4] x86: suppress SMAP and SMEP while running 32-bit PV guest code
Date: Wed, 9 Mar 2016 13:35:29 +0000	[thread overview]
Message-ID: <E959C4978C3B6342920538CF579893F00C36A634@SHSMSX104.ccr.corp.intel.com> (raw)
In-Reply-To: <56E018CE02000078000E430D@prv-mh.provo.novell.com>



> -----Original Message-----
> From: Jan Beulich [mailto:jbeulich@suse.com]
> Sent: Wednesday, March 9, 2016 8:37 PM
> To: andrew.cooper3@citrix.com; Wu, Feng <feng.wu@intel.com>; xen-
> devel@lists.xenproject.org
> Cc: keir@xen.org
> Subject: Re: [PATCH 2/4] x86: suppress SMAP and SMEP while running 32-bit PV
> guest code
> 
> >>>> Andrew Cooper <andrew.cooper3@citrix.com> 03/09/16 1:33 PM >>>
> >On 09/03/16 12:27, Wu, Feng wrote:
> >> Oh, thanks for the clarification! Do you know how "An NMI or #MC may
> occur
> >> between clearing CR4.SMEP and CR4.SMAP in compat_restore_all_guest and
> >> it actually returning to guest context, in which case the guest would run with
> >> the two features enabled. " can happen? Especially how the guest can run
> >> with the two features enabled?
> >
> >NMIs and MCEs can occur at any point, even if interrupts are disabled.
> >
> >The bad situation is this sequence:
> >
> >* Xen is returning to the guest and disables CR4.SMEP/SMAP
> >* NMI occurs while still in Xen
> >* NMI exit path sees it is returning to Xen and re-enabled CR4.SMEP/SMAP
> 
> Well, almost: Re-enabling happens on the NMI entry path. The NMI exit
> path would, seeing it's returning to Xen context, simply not disable them
> again.

Thinking about this again, in this case, when the NMI happens, we are in
Xen context (CPL in cs is 0), so the CPL of the saved cs in stack is 0,right?
why do we re-enable CR4.SMEP/SMAP in this case? I mean do we only
need to enable SMEP/SMAP when coming from 32bit pv guest (CPL of cs is 1) ?

Thanks,
Feng

> 
> Jan
> 
> >* Xen ends up returning to guest with CR4.SMEP/SMAP enabled.
> >
> >~Andrew
> 


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  parent reply	other threads:[~2016-03-09 13:35 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-03-04 11:08 [PATCH 0/4] x86: accommodate 32-bit PV guests with SMAP/SMEP handling Jan Beulich
2016-03-04 11:27 ` [PATCH 1/4] x86/alternatives: correct near branch check Jan Beulich
2016-03-07 15:43   ` Andrew Cooper
2016-03-07 15:56     ` Jan Beulich
2016-03-07 16:11       ` Andrew Cooper
2016-03-07 16:21         ` Jan Beulich
2016-03-08 17:33           ` Andrew Cooper
2016-03-04 11:27 ` [PATCH 2/4] x86: suppress SMAP and SMEP while running 32-bit PV guest code Jan Beulich
2016-03-07 16:59   ` Andrew Cooper
2016-03-08  7:57     ` Jan Beulich
2016-03-09  8:09       ` Wu, Feng
2016-03-09 14:09         ` Jan Beulich
2016-03-09 11:19       ` Andrew Cooper
2016-03-09 14:28         ` Jan Beulich
2016-03-09  8:09   ` Wu, Feng
2016-03-09 10:45     ` Andrew Cooper
2016-03-09 12:27       ` Wu, Feng
2016-03-09 12:33         ` Andrew Cooper
2016-03-09 12:36           ` Jan Beulich
2016-03-09 12:54             ` Wu, Feng
2016-03-09 13:35             ` Wu, Feng [this message]
2016-03-09 13:42               ` Andrew Cooper
2016-03-09 14:03       ` Jan Beulich
2016-03-09 14:07     ` Jan Beulich
2016-03-04 11:28 ` [PATCH 3/4] x86: use optimal NOPs to fill the SMAP/SMEP placeholders Jan Beulich
2016-03-07 17:43   ` Andrew Cooper
2016-03-08  8:02     ` Jan Beulich
2016-03-04 11:29 ` [PATCH 4/4] x86: use 32-bit loads for 32-bit PV guest state reload Jan Beulich
2016-03-07 17:45   ` Andrew Cooper
2016-03-10  9:44 ` [PATCH v2 0/3] x86: accommodate 32-bit PV guests with SMEP/SMAP handling Jan Beulich
2016-03-10  9:53   ` [PATCH v2 1/3] x86: suppress SMEP and SMAP while running 32-bit PV guest code Jan Beulich
2016-05-13 15:48     ` Andrew Cooper
2016-03-10  9:54   ` [PATCH v2 2/3] x86: use optimal NOPs to fill the SMEP/SMAP placeholders Jan Beulich
2016-05-13 15:49     ` Andrew Cooper
2016-03-10  9:55   ` [PATCH v2 3/3] x86: use 32-bit loads for 32-bit PV guest state reload Jan Beulich
     [not found]   ` <56E9A0DB02000078000DD54C@prv-mh.provo.novell.com>
2016-03-17  7:50     ` [PATCH v3 0/4] x86: accommodate 32-bit PV guests with SMEP/SMAP handling Jan Beulich
2016-03-17  8:02       ` [PATCH v3 1/4] x86: move cached CR4 value to struct cpu_info Jan Beulich
2016-03-17 16:20         ` Andrew Cooper
2016-03-17  8:03       ` [PATCH v3 2/4] x86: suppress SMEP and SMAP while running 32-bit PV guest code Jan Beulich
2016-03-25 18:01         ` Konrad Rzeszutek Wilk
2016-03-29  6:55           ` Jan Beulich
2016-05-13 15:58         ` Andrew Cooper
2016-03-17  8:03       ` [PATCH v3 3/4] x86: use optimal NOPs to fill the SMEP/SMAP placeholders Jan Beulich
2016-05-13 15:57         ` Andrew Cooper
2016-05-13 16:06           ` Jan Beulich
2016-05-13 16:09             ` Andrew Cooper
2016-03-17  8:04       ` [PATCH v3 4/4] x86: use 32-bit loads for 32-bit PV guest state reload Jan Beulich
2016-03-25 18:02         ` Konrad Rzeszutek Wilk
2016-03-17 16:14       ` [PATCH v3 5/4] x86: reduce code size of struct cpu_info member accesses Jan Beulich
2016-03-25 18:47         ` Konrad Rzeszutek Wilk
2016-03-29  6:59           ` Jan Beulich
2016-03-30 14:28             ` Konrad Rzeszutek Wilk
2016-03-30 14:42               ` Jan Beulich
2016-05-13 16:11         ` Andrew Cooper
2016-05-03 13:58       ` Ping: [PATCH v3 2/4] x86: suppress SMEP and SMAP while running 32-bit PV guest code Jan Beulich
2016-05-03 14:10         ` Andrew Cooper
2016-05-03 14:25           ` Jan Beulich
2016-05-04 10:03             ` Andrew Cooper
2016-05-04 13:35               ` Jan Beulich
2016-05-04  3:07         ` Wu, Feng
2016-05-13 15:21         ` Wei Liu
2016-05-13 15:30           ` Jan Beulich
2016-05-13 15:33             ` Wei Liu
2016-05-13 17:02       ` [PATCH v3 0/4] x86: accommodate 32-bit PV guests with SMEP/SMAP handling Wei Liu
2016-05-13 17:21         ` Andrew Cooper
2016-06-21  6:19       ` Wu, Feng
2016-06-21  7:17         ` Jan Beulich

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