@@ -106,6 +106,10 @@ static inline bool cpu_has_load_perf_global_ctrl(void)
return vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL;
}
+static inline bool cpu_has_load_cet_ctrl(void)
+{
+ return (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_CET_STATE);
+}
static inline bool cpu_has_vmx_mpx(void)
{
return vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_BNDCFGS;
@@ -4371,6 +4371,21 @@ void vmx_set_constant_host_state(struct vcpu_vmx *vmx)
if (cpu_has_load_ia32_efer())
vmcs_write64(HOST_IA32_EFER, host_efer);
+
+ /*
+ * Supervisor shadow stack is not enabled on host side, i.e.,
+ * host IA32_S_CET.SHSTK_EN bit is guaranteed to 0 now, per SDM
+ * description(RDSSP instruction), SSP is not readable in CPL0,
+ * so resetting the two registers to 0s at VM-Exit does no harm
+ * to kernel execution. When execution flow exits to userspace,
+ * SSP is reloaded from IA32_PL3_SSP. Check SDM Vol.2A/B Chapter
+ * 3 and 4 for details.
+ */
+ if (cpu_has_load_cet_ctrl()) {
+ vmcs_writel(HOST_S_CET, host_s_cet);
+ vmcs_writel(HOST_SSP, 0);
+ vmcs_writel(HOST_INTR_SSP_TABLE, 0);
+ }
}
void set_cr4_guest_host_mask(struct vcpu_vmx *vmx)
@@ -114,6 +114,8 @@ static u64 __read_mostly efer_reserved_bits = ~((u64)EFER_SCE);
#endif
static u64 __read_mostly cr4_reserved_bits = CR4_RESERVED_BITS;
+u64 __read_mostly host_s_cet;
+EXPORT_SYMBOL_GPL(host_s_cet);
#define KVM_EXIT_HYPERCALL_VALID_MASK (1 << KVM_HC_MAP_GPA_RANGE)
@@ -9840,6 +9842,18 @@ static int __kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
return -EIO;
}
+ if (boot_cpu_has(X86_FEATURE_SHSTK)) {
+ rdmsrl(MSR_IA32_S_CET, host_s_cet);
+ /*
+ * Linux doesn't yet support supervisor shadow stacks (SSS), so
+ * KVM doesn't save/restore the associated MSRs, i.e. KVM may
+ * clobber the host values. Yell and refuse to load if SSS is
+ * unexpectedly enabled, e.g. to avoid crashing the host.
+ */
+ if (WARN_ON_ONCE(host_s_cet & CET_SHSTK_EN))
+ return -EIO;
+ }
+
x86_emulator_cache = kvm_alloc_emulator_cache();
if (!x86_emulator_cache) {
pr_err("failed to allocate cache for x86 emulator\n");
@@ -325,6 +325,7 @@ fastpath_t handle_fastpath_set_msr_irqoff(struct kvm_vcpu *vcpu);
extern u64 host_xcr0;
extern u64 host_xss;
extern u64 host_arch_capabilities;
+extern u64 host_s_cet;
extern struct kvm_caps kvm_caps;
Save constant values to HOST_{S_CET,SSP,INTR_SSP_TABLE} field explicitly. Kernel IBT is supported and the setting in MSR_IA32_S_CET is static after post-boot(The exception is BIOS call case but vCPU thread never across it) and KVM doesn't need to refresh HOST_S_CET field before every VM-Enter/ VM-Exit sequence. Host supervisor shadow stack is not enabled now and SSP is not accessible to kernel mode, thus it's safe to set host IA32_INT_SSP_TAB/SSP VMCS field to 0s. When shadow stack is enabled for CPL3, SSP is reloaded from PL3_SSP before it exits to userspace. Check SDM Vol 2A/B Chapter 3/4 for SYSCALL/ SYSRET/SYSENTER SYSEXIT/RDSSP/CALL etc. Prevent KVM module loading if host supervisor shadow stack SHSTK_EN is set in MSR_IA32_S_CET as KVM cannot co-exit with it correctly. Suggested-by: Sean Christopherson <seanjc@google.com> Suggested-by: Chao Gao <chao.gao@intel.com> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com> Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com> --- arch/x86/kvm/vmx/capabilities.h | 4 ++++ arch/x86/kvm/vmx/vmx.c | 15 +++++++++++++++ arch/x86/kvm/x86.c | 14 ++++++++++++++ arch/x86/kvm/x86.h | 1 + 4 files changed, 34 insertions(+)