Messages in this thread | | | Date | Mon, 24 Jan 2022 16:23:09 +0000 | From | Sean Christopherson <> | Subject | Re: [PATCH] KVM: x86/cpuid: Exclude unpermitted xfeatures for vcpu->arch.guest_supported_xcr0 |
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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 ?
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