From: Sean Christopherson <seanjc@google.com>
To: Like Xu <like.xu.linux@gmail.com>
Cc: "Tian, Kevin" <kevin.tian@intel.com>,
Paolo Bonzini <pbonzini@redhat.com>,
"Liu, Jing2" <jing2.liu@intel.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Joerg Roedel <joro@8bytes.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] KVM: x86/cpuid: Exclude unpermitted xfeatures for vcpu->arch.guest_supported_xcr0
Date: Mon, 24 Jan 2022 16:23:09 +0000 [thread overview]
Message-ID: <Ye7SbfPL/QAjOI6s@google.com> (raw)
In-Reply-To: <38c1fbc3-d770-48f3-5432-8fa1fde033f5@gmail.com>
On Mon, Jan 24, 2022, Like Xu wrote:
> On 24/1/2022 3:06 pm, Tian, Kevin wrote:
> > > From: Like Xu <like.xu.linux@gmail.com>
> > > Sent: Sunday, January 23, 2022 1:50 PM
> > >
> > > From: Like Xu <likexu@tencent.com>
> > >
> > > A malicious user space can bypass xstate_get_guest_group_perm() in the
> > > KVM_GET_SUPPORTED_CPUID mechanism and obtain unpermitted xfeatures,
> > > since the validity check of xcr0 depends only on guest_supported_xcr0.
> >
> > Unpermitted xfeatures cannot pass kvm_check_cpuid()...
>
> Indeed, 5ab2f45bba4894a0db4af8567da3efd6228dd010.
>
> This part of logic is pretty fragile and fragmented due to semantic
> inconsistencies between supported_xcr0 and guest_supported_xcr0
> in other three places:
There are no inconsistencies, at least not in the examples below, as the examples
are intended to work in host context. guest_supported_xcr0 is about what the guest
is/isn't allowed to access, it has no bearing on what host userspace can/can't do.
Or are you talking about a different type of inconsistency?
> - __do_cpuid_func
Reporting what KVM supports to host userspace.
> - kvm_mpx_supported
This is a check on host support.
> - kvm_vcpu_ioctl_x86_set_xsave
"write" from host userspace.
> Have you identified all their areas of use ?
next prev parent reply other threads:[~2022-01-24 16:23 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-23 5:50 [PATCH] KVM: x86/cpuid: Exclude unpermitted xfeatures for vcpu->arch.guest_supported_xcr0 Like Xu
2022-01-24 7:06 ` Tian, Kevin
2022-01-24 7:17 ` Like Xu
2022-01-24 16:23 ` Sean Christopherson [this message]
2022-01-24 16:29 ` Paolo Bonzini
2022-01-25 1:54 ` Tian, Kevin
2022-01-25 8:27 ` Paolo Bonzini
2022-01-26 1:23 ` Tian, Kevin
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