linux-kernel - Re: [PATCH v16 21/51] KVM: x86/mmu: WARN on attempt to check permissions for Shadow Stack #PF

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Message-ID: <eb2465a7-359c-41b7-9687-984537f75d96@intel.com>
Date: Tue, 23 Sep 2025 22:33:04 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>,
 Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
 linux-kernel@...r.kernel.org, Tom Lendacky <thomas.lendacky@....com>,
 Mathias Krause <minipli@...ecurity.net>, John Allen <john.allen@....com>,
 Rick Edgecombe <rick.p.edgecombe@...el.com>, Chao Gao <chao.gao@...el.com>,
 Maxim Levitsky <mlevitsk@...hat.com>, Zhang Yi Z
 <yi.z.zhang@...ux.intel.com>, Xin Li <xin@...or.com>
Subject: Re: [PATCH v16 21/51] KVM: x86/mmu: WARN on attempt to check
 permissions for Shadow Stack #PF

On 9/22/2025 3:46 PM, Binbin Wu wrote:
> 
> 
> On 9/22/2025 3:17 PM, Binbin Wu wrote:
>>
>>
>> On 9/20/2025 6:32 AM, Sean Christopherson wrote:
>>> Add PFERR_SS_MASK, a.k.a. Shadow Stack access, and WARN if KVM 
>>> attempts to
>>> check permissions for a Shadow Stack access as KVM hasn't been taught to
>>> understand the magic Writable=0,Dirty=0 combination that is required for
> Typo:
> 
> Writable=0,Dirty=0 -> Writable=0,Dirty=1

With it fixed,

Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>

>>> Shadow Stack accesses, and likely will never learn.  There are no 
>>> plans to
>>> support Shadow Stacks with the Shadow MMU, and the emulator rejects all
>>> instructions that affect Shadow Stacks, i.e. it should be impossible for
>>> KVM to observe a #PF due to a shadow stack access.
>>>
>>> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
>>
>> Reviewed-by: Binbin Wu <binbin.wu@...ux.intel.com>