[PATCH v3 10/21] KVM:x86: Add #CP support in guest exception classification

Yang Weijiang
2023-05-11T07:14:24Z

Add handling for Control Protection (#CP) exceptions(vector 21).
The new vector is introduced for Intel's Control-Flow Enforcement
Technology (CET) relevant violation cases.

Although #CP belongs contributory exception class, but the actual
effect is conditional on CET being exposed to guest. If CET is not
available to guest, #CP falls back to non-contributory and doesn't
have an error code. The rational is used to fix one unit test failure
encountered in L1. Although the issue now is fixed in unit test case,
keep the handling is reasonable. cr4_guest_rsvd_bits is used to avoid
guest_cpuid_has() lookups.

Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
---
arch/x86/include/uapi/asm/kvm.h | 1 +
arch/x86/kvm/vmx/nested.c | 2 +-
arch/x86/kvm/x86.c | 10 +++++++---
arch/x86/kvm/x86.h | 13 ++++++++++---
4 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index 7f467fe05d42..1c002abe2be8 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -33,6 +33,7 @@
#define MC_VECTOR 18
#define XM_VECTOR 19
#define VE_VECTOR 20
+#define CP_VECTOR 21

/* Select x86 specific features in <linux/kvm.h> */
#define __KVM_HAVE_PIT
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 96ede74a6067..7bc62cd72748 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -2850,7 +2850,7 @@ static int nested_check_vm_entry_controls(struct kvm_vcpu *vcpu,
/* VM-entry interruption-info field: deliver error code */
should_have_error_code =
intr_type == INTR_TYPE_HARD_EXCEPTION && prot_mode &&
- x86_exception_has_error_code(vector);
+ x86_exception_has_error_code(vcpu, vector);
if (CC(has_error_code != should_have_error_code))
return -EINVAL;

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7788646bbf1f..a768cbf3fbb7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -520,11 +520,15 @@ EXPORT_SYMBOL_GPL(kvm_spurious_fault);
#define EXCPT_CONTRIBUTORY 1
#define EXCPT_PF 2

-static int exception_class(int vector)
+static int exception_class(struct kvm_vcpu *vcpu, int vector)
{
switch (vector) {
case PF_VECTOR:
return EXCPT_PF;
+ case CP_VECTOR:
+ if (vcpu->arch.cr4_guest_rsvd_bits & X86_CR4_CET)
+ return EXCPT_BENIGN;
+ return EXCPT_CONTRIBUTORY;
case DE_VECTOR:
case TS_VECTOR:
case NP_VECTOR:
@@ -707,8 +711,8 @@ static void kvm_multiple_exception(struct kvm_vcpu *vcpu,
kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
return;
}
- class1 = exception_class(prev_nr);
- class2 = exception_class(nr);
+ class1 = exception_class(vcpu, prev_nr);
+ class2 = exception_class(vcpu, nr);
if ((class1 == EXCPT_CONTRIBUTORY && class2 == EXCPT_CONTRIBUTORY) ||
(class1 == EXCPT_PF && class2 != EXCPT_BENIGN)) {
/*
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index c544602d07a3..2ba7c7fc4846 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -171,13 +171,20 @@ static inline bool is_64_bit_hypercall(struct kvm_vcpu *vcpu)
return vcpu->arch.guest_state_protected || is_64_bit_mode(vcpu);
}

-static inline bool x86_exception_has_error_code(unsigned int vector)
+static inline bool x86_exception_has_error_code(struct kvm_vcpu *vcpu,
+ unsigned int vector)
{
static u32 exception_has_error_code = BIT(DF_VECTOR) | BIT(TS_VECTOR) |
BIT(NP_VECTOR) | BIT(SS_VECTOR) | BIT(GP_VECTOR) |
- BIT(PF_VECTOR) | BIT(AC_VECTOR);
+ BIT(PF_VECTOR) | BIT(AC_VECTOR) | BIT(CP_VECTOR);

- return (1U << vector) & exception_has_error_code;
+ if (!((1U << vector) & exception_has_error_code))
+ return false;
+
+ if (vector == CP_VECTOR)
+ return !(vcpu->arch.cr4_guest_rsvd_bits & X86_CR4_CET);
+
+ return true;
}

static inline bool mmu_is_nested(struct kvm_vcpu *vcpu)
--
2.27.0