From: Sean Christopherson <seanjc@xxxxxxxxxx>
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@xxxxxxxxxx>
Reviewed-by: Kai Huang <kai.huang@xxxxxxxxx>
Reviewed-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>
Message-ID: <20240228024147.41573-8-seanjc@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 6 ++++++
arch/x86/kvm/mmu/mmu.c | 14 +++-----------
arch/x86/kvm/svm/svm.c | 9 +++++++++
3 files changed, 18 insertions(+), 11 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 58bbcf76ad1e..12e727301262 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -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 | \
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index c72a2033ca96..5562d693880a 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4502,6 +4502,9 @@ 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);
@@ -5786,17 +5789,6 @@ 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;
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 0f3b59da0d4a..535018f152a3 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -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) ?
--
2.43.0
