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SubjectRe: [PATCH v15 04/14] KVM: x86: Add #CP support in guest exception dispatch
On Wed, Feb 03, 2021, Yang Weijiang wrote:
> Add handling for Control Protection (#CP) exceptions, vector 21, used
> and introduced by Intel's Control-Flow Enforcement Technology (CET).
> relevant CET violation case. See Intel's SDM for details.
>
> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> ---
> arch/x86/include/uapi/asm/kvm.h | 1 +
> arch/x86/kvm/x86.c | 1 +
> arch/x86/kvm/x86.h | 2 +-
> 3 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
> index 8e76d3701db3..507263d1d0b2 100644
> --- a/arch/x86/include/uapi/asm/kvm.h
> +++ b/arch/x86/include/uapi/asm/kvm.h
> @@ -32,6 +32,7 @@
> #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/x86.c b/arch/x86/kvm/x86.c
> index 99f787152d12..d9d3bae40a8c 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -436,6 +436,7 @@ static int exception_class(int vector)
> case NP_VECTOR:
> case SS_VECTOR:
> case GP_VECTOR:
> + case CP_VECTOR:
> return EXCPT_CONTRIBUTORY;
> default:
> break;
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index c5ee0f5ce0f1..bdbd0b023ecc 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -116,7 +116,7 @@ static inline bool x86_exception_has_error_code(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);

These need to be conditional on CET being exposed to the guest. TBD exceptions
are non-contributory and don't have an error code. Found when running unit
tests in L1 with a kvm/queue as L1, but an older L0. cr4_guest_rsvd_bits can be
used to avoid guest_cpuid_has() lookups.

The SDM also gets this wrong. Section 26.2.1.3, VM-Entry Control Fields, needs
to be updated to add #CP to the list.

— The field's deliver-error-code bit (bit 11) is 1 if each of the following
holds: (1) the interruption type is hardware exception; (2) bit 0
(corresponding to CR0.PE) is set in the CR0 field in the guest-state area;
(3) IA32_VMX_BASIC[56] is read as 0 (see Appendix A.1); and (4) the vector
indicates one of the following exceptions: #DF (vector 8), #TS (10),
#NP (11), #SS (12), #GP (13), #PF (14), or #AC (17).

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index dbca1687ae8e..0b6dab6915a3 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -2811,7 +2811,7 @@ 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 28fea7ff7a86..0288d6a364bd 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -437,17 +437,20 @@ 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:
case SS_VECTOR:
case GP_VECTOR:
- case CP_VECTOR:
return EXCPT_CONTRIBUTORY;
default:
break;
@@ -588,8 +591,8 @@ 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 a14da36a30ed..dce756ffb577 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -120,12 +120,16 @@ static inline bool is_la57_mode(struct kvm_vcpu *vcpu)
#endif
}

-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(CP_VECTOR);

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



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