[v9,36/84] KVM: x86: disable gpa_available optimization for fetch and page-walk SPT violations

Commit Message

Adalbert Lazăr July 21, 2020, 9:08 p.m. UTC

From: Mircea Cîrjaliu <[e-mail]>

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

Signed-off-by: Mircea Cîrjaliu <[e-mail]>
Co-developed-by: Adalbert Lazăr <[e-mail]>
Signed-off-by: Adalbert Lazăr <[e-mail]>
---
 arch/x86/include/asm/kvm_host.h | 5 +++++
 arch/x86/kvm/mmu/mmu.c          | 8 ++++++++
 arch/x86/kvm/x86.c              | 2 +-
 3 files changed, 14 insertions(+), 1 deletion(-)

Patch

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index b6a1704e0f89..8a119fb7c623 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1436,6 +1436,10 @@  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).
@@ -1458,6 +1462,7 @@  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 da57321e0cec..4df5b729e2c5 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5566,6 +5566,14 @@  int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 error_code,
 	 */
 	if (!mmio_info_in_cache(vcpu, cr2_or_gpa, direct) && !is_guest_mode(vcpu))
 		emulation_type |= EMULTYPE_ALLOW_RETRY_PF;
+
+	/*
+	 * 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;
 emulate:
 	/*
 	 * On AMD platforms, under certain conditions insn_len may be zero on #NPF.
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7668ca5b8a7a..ffcf09e9bf78 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6987,7 +6987,7 @@  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;
 		}