linux-kernel - Re: [PATCH v10 27/27] KVM: x86: Don't emulate instructions guarded by CET

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Message-ID: <ZjLPJzh2OmrYW-JN@google.com>
Date: Wed, 1 May 2024 16:24:23 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Yang Weijiang <weijiang.yang@...el.com>
Cc: pbonzini@...hat.com, dave.hansen@...el.com, x86@...nel.org, 
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, peterz@...radead.org, 
	chao.gao@...el.com, rick.p.edgecombe@...el.com, mlevitsk@...hat.com, 
	john.allen@....com
Subject: Re: [PATCH v10 27/27] KVM: x86: Don't emulate instructions guarded by CET

On Sun, Feb 18, 2024, Yang Weijiang wrote:
> Don't emulate the branch instructions, e.g., CALL/RET/JMP etc., when CET
> is active in guest, return KVM_INTERNAL_ERROR_EMULATION to userspace to
> handle it.
> 
> KVM doesn't emulate CPU behaviors to check CET protected stuffs while
> emulating guest instructions, instead it stops emulation on detecting
> the instructions in process are CET protected. By doing so, it can avoid
> generating bogus #CP in guest and preventing CET protected execution flow
> subversion from guest side.
> 
> Suggested-by: Chao Gao <chao.gao@...el.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> ---

This should be ordered before CET is exposed to userspace, e.g. so that KVM's
ABI is well defined when CET support because usable.