[RFC PATCH v2 4/6] KVM: SVM: Save shadow stack host state on VMRUN

John Allen
2023-05-24T15:55:07Z

When running as an SEV-ES guest, the PL0_SSP, PL1_SSP, PL2_SSP, PL3_SSP,
and U_CET fields in the VMCB save area are type B, meaning the host
state is automatically loaded on a VMEXIT, but is not saved on a VMRUN.
The other shadow stack MSRs, S_CET, SSP, and ISST_ADDR are type A,
meaning they are loaded on VMEXIT and saved on VMRUN. Manually save the
type B host MSR values before VMRUN.

Signed-off-by: John Allen <john.allen@amd.com>
---
arch/x86/kvm/svm/sev.c | 13 +++++++++++++
1 file changed, 13 insertions(+)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index c25aeb550cd9..03dd68bddd51 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -3028,6 +3028,19 @@ void sev_es_prepare_switch_to_guest(struct sev_es_save_area *hostsa)

/* MSR_IA32_XSS is restored on VMEXIT, save the currnet host value */
hostsa->xss = host_xss;
+
+ if (boot_cpu_has(X86_FEATURE_SHSTK)) {
+ /*
+ * MSR_IA32_U_CET, MSR_IA32_PL0_SSP, MSR_IA32_PL1_SSP,
+ * MSR_IA32_PL2_SSP, and MSR_IA32_PL3_SSP are restored on
+ * VMEXIT, save the current host values.
+ */
+ rdmsrl(MSR_IA32_U_CET, hostsa->u_cet);
+ rdmsrl(MSR_IA32_PL0_SSP, hostsa->vmpl0_ssp);
+ rdmsrl(MSR_IA32_PL1_SSP, hostsa->vmpl1_ssp);
+ rdmsrl(MSR_IA32_PL2_SSP, hostsa->vmpl2_ssp);
+ rdmsrl(MSR_IA32_PL3_SSP, hostsa->vmpl3_ssp);
+ }
}

void sev_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector)
--
2.39.1