Re: [PATCH v3 12/21] KVM:x86: Add fault checks for guest CR4.CET setting

[Chao Gao]

On Thu, May 11, 2023 at 12:08:48AM -0400, Yang Weijiang wrote:
>Check potential faults for CR4.CET setting per Intel SDM.

>CR4.CET is the master control bit for CET features (SHSTK and IBT).
>In addition to basic support checks,

To me, this implies some checks against CR4.CET when enabling SHSTK or
IBT. but the checks are not added by this patch. Then, why bother to
mention this?

>CET can be enabled if and only
>if CR0.WP==1, i.e. setting CR4.CET=1 faults if CR0.WP==0 and setting
>CR0.WP=0 fails if CR4.CET==1.
>
>Co-developed-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
>Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
>Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
>---
> arch/x86/kvm/x86.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
>diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>index a768cbf3fbb7..b6eec9143129 100644
>--- a/arch/x86/kvm/x86.c
>+++ b/arch/x86/kvm/x86.c
>@@ -995,6 +995,9 @@ int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
> 	    (is_64_bit_mode(vcpu) || kvm_is_cr4_bit_set(vcpu, X86_CR4_PCIDE)))
> 		return 1;
> 
>+	if (!(cr0 & X86_CR0_WP) && kvm_is_cr4_bit_set(vcpu, X86_CR4_CET))
>+		return 1;
>+
> 	static_call(kvm_x86_set_cr0)(vcpu, cr0);
> 
> 	kvm_post_set_cr0(vcpu, old_cr0, cr0);
>@@ -1210,6 +1213,9 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
> 			return 1;
> 	}
> 
>+	if ((cr4 & X86_CR4_CET) && !kvm_is_cr0_bit_set(vcpu, X86_CR0_WP))
>+		return 1;
>+
> 	static_call(kvm_x86_set_cr4)(vcpu, cr4);
> 
> 	kvm_post_set_cr4(vcpu, old_cr4, cr4);
>-- 
>2.27.0
>