[PATCH v12 28/77] KVM: x86: disable gpa_available optimization for fetch and page-walk SPT violations

Adalbert Lazăr
2021-10-06T17:30:24Z

From: Mircea C?rjaliu <mcirjaliu at bitdefender.com>

This change is needed because the introspection tool can write-protect
guest page tables or exec-protect heap/stack pages.

Signed-off-by: Mircea C?rjaliu <mcirjaliu at bitdefender.com>
Co-developed-by: Adalbert Laz?r <alazar at bitdefender.com>
Signed-off-by: Adalbert Laz?r <alazar at bitdefender.com>
---
 arch/x86/include/asm/kvm_host.h | 5 +++++
 arch/x86/kvm/mmu/mmu.c          | 7 +++++++
 arch/x86/kvm/x86.c              | 2 +-
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 692e55a5c312..dc3c83edc4bc 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1664,6 +1664,10 @@ extern u64 kvm_mce_cap_supported;
  *			     retry native execution under certain conditions,
  *			     Can only be set in conjunction with EMULTYPE_PF.
  *
+ * EMULTYPE_GPA_AVAILABLE_PF - Set when the emulator can avoid a page walk
+ *                           to get the GPA.
+ *                           Can only be set in conjunction with EMULTYPE_PF.
+ *
  * EMULTYPE_TRAP_UD_FORCED - Set when emulating an intercepted #UD that was
  *			     triggered by KVM's magic "force emulation" prefix,
  *			     which is opt in via module param (off by default).
@@ -1686,6 +1690,7 @@ extern u64 kvm_mce_cap_supported;
 #define EMULTYPE_TRAP_UD_FORCED	    (1 << 4)
 #define EMULTYPE_VMWARE_GP	    (1 << 5)
 #define EMULTYPE_PF		    (1 << 6)
+#define EMULTYPE_GPA_AVAILABLE_PF   (1 << 7)

 int kvm_emulate_instruction(struct kvm_vcpu *vcpu, int emulation_type);
 int kvm_emulate_instruction_from_buffer(struct kvm_vcpu *vcpu,
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index b5685e342945..c90683284098 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5297,6 +5297,13 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t
cr2_or_gpa, u64 error_code,

 	if (WARN_ON(!VALID_PAGE(vcpu->arch.mmu->root_hpa)))
 		return RET_PF_RETRY;
+	/*
+	 * With shadow page tables, fault_address contains a GVA or nGPA.
+	 * On a fetch fault, fault_address contains the instruction pointer.
+	 */
+	if (direct && likely(!(error_code & PFERR_FETCH_MASK)) &&
+	    (error_code & PFERR_GUEST_FINAL_MASK))
+		emulation_type |= EMULTYPE_GPA_AVAILABLE_PF;

 	r = RET_PF_INVALID;
 	if (unlikely(error_code & PFERR_RSVD_MASK)) {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c52ac5e9a020..ab97e0175c04 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7933,7 +7933,7 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t
cr2_or_gpa,
 		ctxt->exception.address = cr2_or_gpa;

 		/* With shadow page tables, cr2 contains a GVA or nGPA. */
-		if (vcpu->arch.mmu->direct_map) {
+		if (emulation_type & EMULTYPE_GPA_AVAILABLE_PF) {
 			ctxt->gpa_available = true;
 			ctxt->gpa_val = cr2_or_gpa;
 		}