Re: [PATCH] KVM: vmx: add mismatched size in vmcs_check32

From: Haiwei Li <lihaiwei.kernel@gmail.com>
To: Sean Christopherson <seanjc@google.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
	kvm list <kvm@vger.kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	Haiwei Li <lihaiwei@tencent.com>
Subject: Re: [PATCH] KVM: vmx: add mismatched size in vmcs_check32
Date: Fri, 9 Apr 2021 09:57:57 +0800	[thread overview]
Message-ID: <CAB5KdObQ=HN2YBZCB2iV5U_uuOuwtgrX=CcApstwKwHeaRqy8w@mail.gmail.com> (raw)
In-Reply-To: <YG8pwERmjxYQoquP@google.com>

On Fri, Apr 9, 2021 at 12:05 AM Sean Christopherson <seanjc@google.com> wrote:
>
> On Thu, Apr 08, 2021, lihaiwei.kernel@gmail.com wrote:
> > From: Haiwei Li <lihaiwei@tencent.com>
> >
> > vmcs_check32 misses the check for 64-bit and 64-bit high.
>
> Can you clarify in the changelog that, while it is architecturally legal to
> access 64-bit and 64-bit high fields with a 32-bit read/write in 32-bit mode,
> KVM should never do partial accesses to VMCS fields.  And/or note that the
> 32-bit accesses are done in vmcs_{read,write}64() when necessary?  Hmm, maybe:
>
>   Add compile-time assertions in vmcs_check32() to disallow accesses to
>   64-bit and 64-bit high fields via vmcs_{read,write}32().  Upper level
>   KVM code should never do partial accesses to VMCS fields.  KVM handles
>   the split accesses automatically in vmcs_{read,write}64() when running
>   as a 32-bit kernel.

Good suggestion, thanks. I will send v2.