Messages in this thread | | | Date | Mon, 17 Jan 2022 17:44:15 +0800 | From | Like Xu <> | Subject | Re: [PATCH] KVM: x86: Fix the #GP(0) and #UD conditions for XSETBV emulation |
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Uh, thanks for your prompt response.
On 17/1/2022 4:31 pm, Paolo Bonzini wrote: > On 1/17/22 08:24, Like Xu wrote: >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index 76b4803dd3bd..7d8622e592bb 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -1024,7 +1024,11 @@ static int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 >> index, u64 xcr) >> int kvm_emulate_xsetbv(struct kvm_vcpu *vcpu) >> { >> - if (static_call(kvm_x86_get_cpl)(vcpu) != 0 || >> + if (!guest_cpuid_has(vcpu, X86_FEATURE_XSAVE) || >> + !kvm_read_cr4_bits(vcpu, X86_CR4_OSXSAVE)) >> + return kvm_handle_invalid_op(vcpu); > > There's no need to check XSAVE, because it XSAVE=0 will prevent setting > CR4.OSXSAVE.
So we just need to check X86_CR4_OSXSAVE for #UD here ?
> > Likewise, CPL and SS.DPL are also defined in real mode so there's no need to > check is_protmode. The Intel manuals sometimes still act as the descriptor > caches don't exist, even though VMX effectively made them part of the architecture.
OK, make sense to drop is_protmode().
> > Also, the "Fixes" tag is not really correct as the behavior was the same > before. Rather, it fixes commit 02d4160fbd76 ("x86: KVM: add xsetbv to the
It seems the original code comes from 81dd35d42c9a ("KVM: SVM: Add xsetbv intercept"). 2acf923e38 ("KVM: VMX: Enable XSAVE/XRSTOR for guest") and 92f9895c146d.
> emulator", 2019-08-22). Checking OSXSAVE is a bug in the emulator path, even > though it's not needed in the XSETBV vmexit case.
The kvm_emulate_xsetbv() has been removed from the emulator path. I'm not really sure why it's not needed in the XSETBV vmexit case. More details ?
> > Thanks, > > Paolo > >> + if ((is_protmode(vcpu) && static_call(kvm_x86_get_cpl)(vcpu) != 0) || >> __kvm_set_xcr(vcpu, kvm_rcx_read(vcpu), kvm_read_edx_eax(vcpu))) { >> kvm_inject_gp(vcpu, 0); >> return 1; > >
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