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Date: Thu, 9 Jul 2020 09:07:43 -0700
From: Andy Lutomirski <luto@...nel.org>
To: Dave Hansen <dave.hansen@...el.com>
Cc: "Andersen, John" <john.s.andersen@...el.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	Sean Christopherson <sean.j.christopherson@...el.com>, Jonathan Corbet <corbet@....net>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>, Shuah Khan <shuah@...nel.org>, 
	Liran Alon <liran.alon@...cle.com>, Andrew Jones <drjones@...hat.com>, 
	Rick Edgecombe <rick.p.edgecombe@...el.com>, 
	Kristen Carlson Accardi <kristen@...ux.intel.com>, Vitaly Kuznetsov <vkuznets@...hat.com>, 
	Wanpeng Li <wanpengli@...cent.com>, Jim Mattson <jmattson@...gle.com>, 
	Joerg Roedel <joro@...tes.org>, Mauro Carvalho Chehab <mchehab+huawei@...nel.org>, 
	Greg KH <gregkh@...uxfoundation.org>, "Paul E. McKenney" <paulmck@...nel.org>, 
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, Juergen Gross <jgross@...e.com>, 
	Mike Kravetz <mike.kravetz@...cle.com>, Oliver Neukum <oneukum@...e.com>, 
	Andrew Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Fenghua Yu <fenghua.yu@...el.com>, reinette.chatre@...el.com, 
	vineela.tummalapalli@...el.com, Dave Hansen <dave.hansen@...ux.intel.com>, 
	Arjan van de Ven <arjan@...ux.intel.com>, caoj.fnst@...fujitsu.com, 
	Baoquan He <bhe@...hat.com>, Arvind Sankar <nivedita@...m.mit.edu>, 
	Kees Cook <keescook@...omium.org>, Dan Williams <dan.j.williams@...el.com>, eric.auger@...hat.com, 
	aaronlewis@...gle.com, Peter Xu <peterx@...hat.com>, makarandsonare@...gle.com, 
	"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
	kvm list <kvm@...r.kernel.org>, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>, 
	Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH 2/4] KVM: x86: Introduce paravirt feature CR0/CR4 pinning

On Thu, Jul 9, 2020 at 8:56 AM Dave Hansen <dave.hansen@...el.com> wrote:
>
> On 7/9/20 8:44 AM, Andersen, John wrote:
> >
> >         Bits which are allowed to be pinned default to WP for CR0 and SMEP,
> >         SMAP, and UMIP for CR4.
>
> I think it also makes sense to have FSGSBASE in this set.
>
> I know it hasn't been tested, but I think we should do the legwork to
> test it.  If not in this set, can we agree that it's a logical next step?

I have no objection to pinning FSGSBASE, but is there a clear
description of the threat model that this whole series is meant to
address?  The idea is to provide a degree of protection against an
attacker who is able to convince a guest kernel to write something
inappropriate to CR4, right?  How realistic is this?

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