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KVM: x86: Move synthetic PFERR_* sanity checks to SVM's #NPF handler

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Move the sanity check that hardware never sets bits that collide with KVM-
define synthetic bits from kvm_mmu_page_fault() to npf_interception(),
i.e. make the sanity check #NPF specific.  The legacy #PF path already
WARNs if _any_ of bits 63:32 are set, and the error code that comes from
VMX's EPT Violatation and Misconfig is 100% synthesized (KVM morphs VMX's
EXIT_QUALIFICATION into error code flags).

Add a compile-time assert in the legacy #PF handler to make sure that KVM-
define flags are covered by its existing sanity check on the upper bits.

Opportunistically add a description of PFERR_IMPLICIT_ACCESS, since we
are removing the comment that defined it.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Message-ID: <20240228024147.41573-8-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2024-04-17 07:30:29 -04:00 • committed by Paolo Bonzini
parent 9b62e03e19
commit dee281e4b4
3 changed files with 18 additions and 11 deletions
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6
arch/x86/include/asm/kvm_host.h
View file

@ -267,7 +267,13 @@ enum x86_intercept_stage;
#define PFERR_GUEST_ENC_MASK BIT_ULL(34)
#define PFERR_GUEST_SIZEM_MASK BIT_ULL(35)
#define PFERR_GUEST_VMPL_MASK BIT_ULL(36)
/*
* IMPLICIT_ACCESS is a KVM-defined flag used to correctly perform SMAP checks
* when emulating instructions that triggers implicit access.
*/
#define PFERR_IMPLICIT_ACCESS BIT_ULL(48)
#define PFERR_SYNTHETIC_MASK (PFERR_IMPLICIT_ACCESS)
#define PFERR_NESTED_GUEST_PAGE (PFERR_GUEST_PAGE_MASK | \
PFERR_WRITE_MASK | \

14
arch/x86/kvm/mmu/mmu.c
View file

@ -4501,6 +4501,9 @@ int kvm_handle_page_fault(struct kvm_vcpu *vcpu, u64 error_code,
return -EFAULT;
#endif
/* Ensure the above sanity check also covers KVM-defined flags. */
BUILD_BUG_ON(lower_32_bits(PFERR_SYNTHETIC_MASK));
vcpu->arch.l1tf_flush_l1d = true;
if (!flags) {
trace_kvm_page_fault(vcpu, fault_address, error_code);
@ -5785,17 +5788,6 @@ int noinline kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 err
int r, emulation_type = EMULTYPE_PF;
bool direct = vcpu->arch.mmu->root_role.direct;
/*
* IMPLICIT_ACCESS is a KVM-defined flag used to correctly perform SMAP
* checks when emulating instructions that triggers implicit access.
* WARN if hardware generates a fault with an error code that collides
* with the KVM-defined value. Clear the flag and continue on, i.e.
* don't terminate the VM, as KVM can't possibly be relying on a flag
* that KVM doesn't know about.
*/
if (WARN_ON_ONCE(error_code & PFERR_IMPLICIT_ACCESS))
error_code &= ~PFERR_IMPLICIT_ACCESS;
if (WARN_ON_ONCE(!VALID_PAGE(vcpu->arch.mmu->root.hpa)))
return RET_PF_RETRY;

9
arch/x86/kvm/svm/svm.c
View file

@ -2047,6 +2047,15 @@ static int npf_interception(struct kvm_vcpu *vcpu)
u64 fault_address = svm->vmcb->control.exit_info_2;
u64 error_code = svm->vmcb->control.exit_info_1;
/*
* WARN if hardware generates a fault with an error code that collides
* with KVM-defined sythentic flags. Clear the flags and continue on,
* i.e. don't terminate the VM, as KVM can't possibly be relying on a
* flag that KVM doesn't know about.
*/
if (WARN_ON_ONCE(error_code & PFERR_SYNTHETIC_MASK))
error_code &= ~PFERR_SYNTHETIC_MASK;
trace_kvm_page_fault(vcpu, fault_address, error_code);
return kvm_mmu_page_fault(vcpu, fault_address, error_code,
static_cpu_has(X86_FEATURE_DECODEASSISTS) ?