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SubjectRe: [PATCH 5.4] KVM: x86: Fix pkru save/restore when guest CR4.PKE=0, move it to x86.c
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On 22/05/20 18:32, Babu Moger wrote:
> [Backported upstream commit 37486135d3a7b03acc7755b63627a130437f066a]
>
> Though rdpkru and wrpkru are contingent upon CR4.PKE, the PKRU
> resource isn't. It can be read with XSAVE and written with XRSTOR.
> So, if we don't set the guest PKRU value here(kvm_load_guest_xsave_state),
> the guest can read the host value.
>
> In case of kvm_load_host_xsave_state, guest with CR4.PKE clear could
> potentially use XRSTOR to change the host PKRU value.
>
> While at it, move pkru state save/restore to common code and the
> host_pkru field to kvm_vcpu_arch. This will let SVM support protection keys.
>
> Cc: stable@vger.kernel.org
> Reported-by: Jim Mattson <jmattson@google.com>
> Signed-off-by: Babu Moger <babu.moger@amd.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> arch/x86/include/asm/kvm_host.h | 1 +
> arch/x86/kvm/vmx/vmx.c | 18 ------------------
> arch/x86/kvm/x86.c | 17 +++++++++++++++++
> 3 files changed, 18 insertions(+), 18 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 4fc61483919a..e204c43ed4b0 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -550,6 +550,7 @@ struct kvm_vcpu_arch {
> unsigned long cr4;
> unsigned long cr4_guest_owned_bits;
> unsigned long cr8;
> + u32 host_pkru;
> u32 pkru;
> u32 hflags;
> u64 efer;
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 04a8212704c1..728758880cb6 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1384,7 +1384,6 @@ void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>
> vmx_vcpu_pi_load(vcpu, cpu);
>
> - vmx->host_pkru = read_pkru();
> vmx->host_debugctlmsr = get_debugctlmsr();
> }
>
> @@ -6541,11 +6540,6 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
>
> kvm_load_guest_xcr0(vcpu);
>
> - if (static_cpu_has(X86_FEATURE_PKU) &&
> - kvm_read_cr4_bits(vcpu, X86_CR4_PKE) &&
> - vcpu->arch.pkru != vmx->host_pkru)
> - __write_pkru(vcpu->arch.pkru);
> -
> pt_guest_enter(vmx);
>
> atomic_switch_perf_msrs(vmx);
> @@ -6634,18 +6628,6 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
>
> pt_guest_exit(vmx);
>
> - /*
> - * eager fpu is enabled if PKEY is supported and CR4 is switched
> - * back on host, so it is safe to read guest PKRU from current
> - * XSAVE.
> - */
> - if (static_cpu_has(X86_FEATURE_PKU) &&
> - kvm_read_cr4_bits(vcpu, X86_CR4_PKE)) {
> - vcpu->arch.pkru = rdpkru();
> - if (vcpu->arch.pkru != vmx->host_pkru)
> - __write_pkru(vmx->host_pkru);
> - }
> -
> kvm_put_guest_xcr0(vcpu);
>
> vmx->nested.nested_run_pending = 0;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 5d530521f11d..502a23313e7b 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -821,11 +821,25 @@ void kvm_load_guest_xcr0(struct kvm_vcpu *vcpu)
> xsetbv(XCR_XFEATURE_ENABLED_MASK, vcpu->arch.xcr0);
> vcpu->guest_xcr0_loaded = 1;
> }
> +
> + if (static_cpu_has(X86_FEATURE_PKU) &&
> + (kvm_read_cr4_bits(vcpu, X86_CR4_PKE) ||
> + (vcpu->arch.xcr0 & XFEATURE_MASK_PKRU)) &&
> + vcpu->arch.pkru != vcpu->arch.host_pkru)
> + __write_pkru(vcpu->arch.pkru);
> }
> EXPORT_SYMBOL_GPL(kvm_load_guest_xcr0);
>
> void kvm_put_guest_xcr0(struct kvm_vcpu *vcpu)
> {
> + if (static_cpu_has(X86_FEATURE_PKU) &&
> + (kvm_read_cr4_bits(vcpu, X86_CR4_PKE) ||
> + (vcpu->arch.xcr0 & XFEATURE_MASK_PKRU))) {
> + vcpu->arch.pkru = rdpkru();
> + if (vcpu->arch.pkru != vcpu->arch.host_pkru)
> + __write_pkru(vcpu->arch.host_pkru);
> + }
> +
> if (vcpu->guest_xcr0_loaded) {
> if (vcpu->arch.xcr0 != host_xcr0)
> xsetbv(XCR_XFEATURE_ENABLED_MASK, host_xcr0);
> @@ -3437,6 +3451,9 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>
> kvm_x86_ops->vcpu_load(vcpu, cpu);
>
> + /* Save host pkru register if supported */
> + vcpu->arch.host_pkru = read_pkru();
> +
> fpregs_assert_state_consistent();
> if (test_thread_flag(TIF_NEED_FPU_LOAD))
> switch_fpu_return();
>

Acked-by: Paolo Bonzini <pbonzini@redhat.com>

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