On Mon, Jan 24, 2022, Like Xu wrote: > On 24/1/2022 3:06 pm, Tian, Kevin wrote: > > > From: Like Xu <like.xu.linux@xxxxxxxxx> > > > Sent: Sunday, January 23, 2022 1:50 PM > > > > > > From: Like Xu <likexu@xxxxxxxxxxx> > > > > > > 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 ?
