On Thu, Jul 25, 2019 at 11:12:43AM +0800, Yang Weijiang wrote:
> "Load Guest CET state" bit controls whether Guest CET states
> will be loaded at Guest entry. Before doing that, KVM needs
> to check if CPU CET feature is enabled on host and available
> to Guest.
>
> Note: SHSTK and IBT features share one control MSR:
> MSR_IA32_{U,S}_CET, which means it's difficult to hide
> one feature from another in the case of SHSTK != IBT,
> after discussed in community, it's agreed to allow Guest
> control two features independently as it won't introduce
> security hole.
>
> Co-developed-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
> Signed-off-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
> Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
> ---
> arch/x86/kvm/vmx/vmx.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index ce5d1e45b7a5..fbf9c335cf7b 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -44,6 +44,7 @@
> #include <asm/spec-ctrl.h>
> #include <asm/virtext.h>
> #include <asm/vmx.h>
> +#include <asm/cet.h>
>
> #include "capabilities.h"
> #include "cpuid.h"
> @@ -2923,6 +2924,18 @@ int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
> if (!nested_vmx_allowed(vcpu) || is_smm(vcpu))
> return 1;
> }
> + if (cpu_x86_cet_enabled() &&
It'd probably be better to check a KVM function here, e.g. a wrapper of
kvm_supported_xss(). I don't think it will ever matter, but it'd be nice
to have a single kill switch given the variety of different enable bits
for CET.
> + (guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) ||
> + guest_cpuid_has(vcpu, X86_FEATURE_IBT))) {
> + if (cr4 & X86_CR4_CET)
> + vmcs_set_bits(VM_ENTRY_CONTROLS,
> + VM_ENTRY_LOAD_GUEST_CET_STATE);
> + else
> + vmcs_clear_bits(VM_ENTRY_CONTROLS,
> + VM_ENTRY_LOAD_GUEST_CET_STATE);
> + } else if (cr4 & X86_CR4_CET) {
> + return 1;
> + }
>
> if (to_vmx(vcpu)->nested.vmxon && !nested_cr4_valid(vcpu, cr4))
> return 1;
> --
> 2.17.2
>
