Re: [PATCH v8 24/26] KVM: x86: Enable CET virtualization for VMX and advertise to userspace
From: Yang, Weijiang
Date: Tue Jan 16 2024 - 20:43:48 EST
On 1/16/2024 3:25 PM, Yuan Yao wrote:
On Thu, Dec 21, 2023 at 09:02:37AM -0500, Yang Weijiang wrote:
Expose CET features to guest if KVM/host can support them, clear CPUID
feature bits if KVM/host cannot support.
Set CPUID feature bits so that CET features are available in guest CPUID.
Add CR4.CET bit support in order to allow guest set CET master control
bit.
Disable KVM CET feature if unrestricted_guest is unsupported/disabled as
KVM does not support emulating CET.
The CET load-bits in VM_ENTRY/VM_EXIT control fields should be set to make
guest CET xstates isolated from host's.
On platforms with VMX_BASIC[bit56] == 0, inject #CP at VMX entry with error
code will fail, and if VMX_BASIC[bit56] == 1, #CP injection with or without
error code is allowed. Disable CET feature bits if the MSR bit is cleared
so that nested VMM can inject #CP if and only if VMX_BASIC[bit56] == 1.
Don't expose CET feature if either of {U,S}_CET xstate bits is cleared
in host XSS or if XSAVES isn't supported.
CET MSR contents after reset, power-up and INIT are set to 0s, clears the
guest fpstate fields so that the guest MSRs are reset to 0s after the events.
Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 2 +-
arch/x86/include/asm/msr-index.h | 1 +
arch/x86/kvm/cpuid.c | 19 +++++++++++++++++--
arch/x86/kvm/vmx/capabilities.h | 6 ++++++
arch/x86/kvm/vmx/vmx.c | 29 ++++++++++++++++++++++++++++-
arch/x86/kvm/vmx/vmx.h | 6 ++++--
arch/x86/kvm/x86.c | 31 +++++++++++++++++++++++++++++--
arch/x86/kvm/x86.h | 3 +++
8 files changed, 89 insertions(+), 8 deletions(-)
...
-#define KVM_SUPPORTED_XSS 0
+#define KVM_SUPPORTED_XSS (XFEATURE_MASK_CET_USER | \
+ XFEATURE_MASK_CET_KERNEL)
u64 __read_mostly host_efer;
EXPORT_SYMBOL_GPL(host_efer);
@@ -9921,6 +9922,20 @@ static int __kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
if (!kvm_cpu_cap_has(X86_FEATURE_XSAVES))
kvm_caps.supported_xss = 0;
+ if (!kvm_cpu_cap_has(X86_FEATURE_SHSTK) &&
+ !kvm_cpu_cap_has(X86_FEATURE_IBT))
+ kvm_caps.supported_xss &= ~(XFEATURE_CET_USER |
+ XFEATURE_CET_KERNEL);
Looks should be XFEATURE_MASK_xxx.
Good catch! Thanks!
+
+ if ((kvm_caps.supported_xss & (XFEATURE_MASK_CET_USER |
+ XFEATURE_MASK_CET_KERNEL)) !=
+ (XFEATURE_MASK_CET_USER | XFEATURE_MASK_CET_KERNEL)) {
+ kvm_cpu_cap_clear(X86_FEATURE_SHSTK);
+ kvm_cpu_cap_clear(X86_FEATURE_IBT);
+ kvm_caps.supported_xss &= ~(XFEATURE_CET_USER |
+ XFEATURE_CET_KERNEL);
Ditto.
Yes.
+ }
+
#define __kvm_cpu_cap_has(UNUSED_, f) kvm_cpu_cap_has(f)
cr4_reserved_bits = __cr4_reserved_bits(__kvm_cpu_cap_has, UNUSED_);
#undef __kvm_cpu_cap_has
@@ -12392,7 +12407,9 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
static inline bool is_xstate_reset_needed(void)
{
- return kvm_cpu_cap_has(X86_FEATURE_MPX);
+ return kvm_cpu_cap_has(X86_FEATURE_MPX) ||
+ kvm_cpu_cap_has(X86_FEATURE_SHSTK) ||
+ kvm_cpu_cap_has(X86_FEATURE_IBT);
}
void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
@@ -12469,6 +12486,16 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
XFEATURE_BNDCSR);
}
+ if (kvm_cpu_cap_has(X86_FEATURE_SHSTK)) {
+ fpstate_clear_xstate_component(fpstate,
+ XFEATURE_CET_USER);
+ fpstate_clear_xstate_component(fpstate,
+ XFEATURE_CET_KERNEL);
+ } else if (kvm_cpu_cap_has(X86_FEATURE_IBT)) {
+ fpstate_clear_xstate_component(fpstate,
+ XFEATURE_CET_USER);
+ }
+
if (init_event)
kvm_load_guest_fpu(vcpu);
}
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 656107e64c93..cc585051d24b 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -533,6 +533,9 @@ bool kvm_msr_allowed(struct kvm_vcpu *vcpu, u32 index, u32 type);
__reserved_bits |= X86_CR4_PCIDE; \
if (!__cpu_has(__c, X86_FEATURE_LAM)) \
__reserved_bits |= X86_CR4_LAM_SUP; \
+ if (!__cpu_has(__c, X86_FEATURE_SHSTK) && \
+ !__cpu_has(__c, X86_FEATURE_IBT)) \
+ __reserved_bits |= X86_CR4_CET; \
__reserved_bits; \
})
--
2.39.3