[v8,21/26] KVM: x86: Save and reload SSP to/from SMRAM
Commit Message
Save CET SSP to SMRAM on SMI and reload it on RSM. KVM emulates HW arch
behavior when guest enters/leaves SMM mode,i.e., save registers to SMRAM
at the entry of SMM and reload them at the exit to SMM. Per SDM, SSP is
one of such registers on 64-bit Arch, and add the support for SSP. Note,
on 32-bit Arch, SSP is not defined in SMRAM, so fail 32-bit CET guest
launch.
Suggested-by: Sean Christopherson <seanjc@google.com>
Suggested-by: Chao Gao <chao.gao@intel.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
---
arch/x86/kvm/cpuid.c | 11 +++++++++++
arch/x86/kvm/smm.c | 8 ++++++++
arch/x86/kvm/smm.h | 2 +-
3 files changed, 20 insertions(+), 1 deletion(-)
Comments
On Thu, 2023-12-21 at 09:02 -0500, Yang Weijiang wrote:
> Save CET SSP to SMRAM on SMI and reload it on RSM. KVM emulates HW arch
> behavior when guest enters/leaves SMM mode,i.e., save registers to SMRAM
> at the entry of SMM and reload them at the exit to SMM. Per SDM, SSP is
> one of such registers on 64-bit Arch, and add the support for SSP. Note,
> on 32-bit Arch, SSP is not defined in SMRAM, so fail 32-bit CET guest
> launch.
>
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Suggested-by: Chao Gao <chao.gao@intel.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> ---
> arch/x86/kvm/cpuid.c | 11 +++++++++++
> arch/x86/kvm/smm.c | 8 ++++++++
> arch/x86/kvm/smm.h | 2 +-
> 3 files changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 3ab133530573..cfc0ac8ddb4a 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -149,6 +149,17 @@ static int kvm_check_cpuid(struct kvm_vcpu *vcpu,
> if (vaddr_bits != 48 && vaddr_bits != 57 && vaddr_bits != 0)
> return -EINVAL;
> }
> + /*
> + * Prevent 32-bit guest from being launched if CET is exposed as SSP
> + * state is not defined for 32-bit SMRAM.
> + */
> + best = cpuid_entry2_find(entries, nent, 0x80000001,
> + KVM_CPUID_INDEX_NOT_SIGNIFICANT);
> + if (best && !(best->edx & F(LM))) {
> + best = cpuid_entry2_find(entries, nent, 0x7, 0);
> + if (best && ((best->ecx & F(SHSTK)) || (best->edx & F(IBT))))
> + return -EINVAL;
> + }
I honestly prefer a check in enter_smm_save_state_32 because SMM might not even
be enabled/used for the guest, and for consistency with SVM check that I added,
but whatever.
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Best regards,
Maxim Levitsky
>
> /*
> * Exposing dynamic xfeatures to the guest requires additional
> diff --git a/arch/x86/kvm/smm.c b/arch/x86/kvm/smm.c
> index 45c855389ea7..7aac9c54c353 100644
> --- a/arch/x86/kvm/smm.c
> +++ b/arch/x86/kvm/smm.c
> @@ -275,6 +275,10 @@ static void enter_smm_save_state_64(struct kvm_vcpu *vcpu,
> enter_smm_save_seg_64(vcpu, &smram->gs, VCPU_SREG_GS);
>
> smram->int_shadow = static_call(kvm_x86_get_interrupt_shadow)(vcpu);
> +
> + if (guest_can_use(vcpu, X86_FEATURE_SHSTK))
> + KVM_BUG_ON(kvm_msr_read(vcpu, MSR_KVM_SSP, &smram->ssp),
> + vcpu->kvm);
> }
> #endif
>
> @@ -564,6 +568,10 @@ static int rsm_load_state_64(struct x86_emulate_ctxt *ctxt,
> static_call(kvm_x86_set_interrupt_shadow)(vcpu, 0);
> ctxt->interruptibility = (u8)smstate->int_shadow;
>
> + if (guest_can_use(vcpu, X86_FEATURE_SHSTK))
> + KVM_BUG_ON(kvm_msr_write(vcpu, MSR_KVM_SSP, smstate->ssp),
> + vcpu->kvm);
> +
> return X86EMUL_CONTINUE;
> }
> #endif
> diff --git a/arch/x86/kvm/smm.h b/arch/x86/kvm/smm.h
> index a1cf2ac5bd78..1e2a3e18207f 100644
> --- a/arch/x86/kvm/smm.h
> +++ b/arch/x86/kvm/smm.h
> @@ -116,8 +116,8 @@ struct kvm_smram_state_64 {
> u32 smbase;
> u32 reserved4[5];
>
> - /* ssp and svm_* fields below are not implemented by KVM */
> u64 ssp;
> + /* svm_* fields below are not implemented by KVM */
> u64 svm_guest_pat;
> u64 svm_host_efer;
> u64 svm_host_cr4;
Best regards,
Maxim Levitsky
@@ -149,6 +149,17 @@ static int kvm_check_cpuid(struct kvm_vcpu *vcpu,
if (vaddr_bits != 48 && vaddr_bits != 57 && vaddr_bits != 0)
return -EINVAL;
}
+ /*
+ * Prevent 32-bit guest from being launched if CET is exposed as SSP
+ * state is not defined for 32-bit SMRAM.
+ */
+ best = cpuid_entry2_find(entries, nent, 0x80000001,
+ KVM_CPUID_INDEX_NOT_SIGNIFICANT);
+ if (best && !(best->edx & F(LM))) {
+ best = cpuid_entry2_find(entries, nent, 0x7, 0);
+ if (best && ((best->ecx & F(SHSTK)) || (best->edx & F(IBT))))
+ return -EINVAL;
+ }
/*
* Exposing dynamic xfeatures to the guest requires additional
@@ -275,6 +275,10 @@ static void enter_smm_save_state_64(struct kvm_vcpu *vcpu,
enter_smm_save_seg_64(vcpu, &smram->gs, VCPU_SREG_GS);
smram->int_shadow = static_call(kvm_x86_get_interrupt_shadow)(vcpu);
+
+ if (guest_can_use(vcpu, X86_FEATURE_SHSTK))
+ KVM_BUG_ON(kvm_msr_read(vcpu, MSR_KVM_SSP, &smram->ssp),
+ vcpu->kvm);
}
#endif
@@ -564,6 +568,10 @@ static int rsm_load_state_64(struct x86_emulate_ctxt *ctxt,
static_call(kvm_x86_set_interrupt_shadow)(vcpu, 0);
ctxt->interruptibility = (u8)smstate->int_shadow;
+ if (guest_can_use(vcpu, X86_FEATURE_SHSTK))
+ KVM_BUG_ON(kvm_msr_write(vcpu, MSR_KVM_SSP, smstate->ssp),
+ vcpu->kvm);
+
return X86EMUL_CONTINUE;
}
#endif
@@ -116,8 +116,8 @@ struct kvm_smram_state_64 {
u32 smbase;
u32 reserved4[5];
- /* ssp and svm_* fields below are not implemented by KVM */
u64 ssp;
+ /* svm_* fields below are not implemented by KVM */
u64 svm_guest_pat;
u64 svm_host_efer;
u64 svm_host_cr4;