KVM: x86: MMU: Move handle_mmio_page_fault() call to kvm_mmu_page_fault()

Rather than placing a handle_mmio_page_fault() call in each
vcpu->arch.mmu.page_fault() handler, moving it up to
kvm_mmu_page_fault() makes the code better:

 - avoids code duplication
 - for kvm_arch_async_page_ready(), which is the other caller of
   vcpu->arch.mmu.page_fault(), removes an extra error_code check
 - avoids returning both RET_MMIO_PF_* values and raw integer values
   from vcpu->arch.mmu.page_fault()
Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

CVE-2018-12207

(cherry picked from commit e9ee956e)
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

arch/x86/kvm/mmu.c

@@ -3405,13 +3405,6 @@ static int nonpaging_page_fault(struct kvm_vcpu *vcpu, gva_t gva,
 
 	pgprintk("%s: gva %lx error %x\n", __func__, gva, error_code);
 
-	if (unlikely(error_code & PFERR_RSVD_MASK)) {
-		r = handle_mmio_page_fault(vcpu, gva, true);
-
-		if (likely(r != RET_MMIO_PF_INVALID))
-			return r;
-	}
-
 	r = mmu_topup_memory_caches(vcpu);
 	if (r)
 		return r;
@@ -3498,13 +3491,6 @@ static int tdp_page_fault(struct kvm_vcpu *vcpu, gva_t gpa, u32 error_code,
 
 	MMU_WARN_ON(!VALID_PAGE(vcpu->arch.mmu.root_hpa));
 
-	if (unlikely(error_code & PFERR_RSVD_MASK)) {
-		r = handle_mmio_page_fault(vcpu, gpa, true);
-
-		if (likely(r != RET_MMIO_PF_INVALID))
-			return r;
-	}
-
 	r = mmu_topup_memory_caches(vcpu);
 	if (r)
 		return r;
@@ -4391,18 +4377,27 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u32 error_code,
 	enum emulation_result er;
 	bool direct = vcpu->arch.mmu.direct_map || mmu_is_nested(vcpu);
 
+	if (unlikely(error_code & PFERR_RSVD_MASK)) {
+		r = handle_mmio_page_fault(vcpu, cr2, direct);
+		if (r == RET_MMIO_PF_EMULATE) {
+			emulation_type = 0;
+			goto emulate;
+		}
+		if (r == RET_MMIO_PF_RETRY)
+			return 1;
+		if (r < 0)
+			return r;
+	}
+
 	r = vcpu->arch.mmu.page_fault(vcpu, cr2, error_code, false);
 	if (r < 0)
-		goto out;
-
-	if (!r) {
-		r = 1;
-		goto out;
-	}
+		return r;
+	if (!r)
+		return 1;
 
 	if (mmio_info_in_cache(vcpu, cr2, direct))
 		emulation_type = 0;
-
+emulate:
 	er = x86_emulate_instruction(vcpu, cr2, emulation_type, insn, insn_len);
 
 	switch (er) {
@@ -4416,8 +4411,6 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u32 error_code,
 	default:
 		BUG();
 	}
-out:
-	return r;
 }
 EXPORT_SYMBOL_GPL(kvm_mmu_page_fault);
 

arch/x86/kvm/paging_tmpl.h

@@ -704,23 +704,16 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code,
 
 	pgprintk("%s: addr %lx err %x\n", __func__, addr, error_code);
 
-	if (unlikely(error_code & PFERR_RSVD_MASK)) {
-		r = handle_mmio_page_fault(vcpu, addr, mmu_is_nested(vcpu));
-		if (likely(r != RET_MMIO_PF_INVALID))
-			return r;
-
-		/*
-		 * page fault with PFEC.RSVD  = 1 is caused by shadow
-		 * page fault, should not be used to walk guest page
-		 * table.
-		 */
-		error_code &= ~PFERR_RSVD_MASK;
-	};
-
 	r = mmu_topup_memory_caches(vcpu);
 	if (r)
 		return r;
 
+	/*
+	 * If PFEC.RSVD is set, this is a shadow page fault.
+	 * The bit needs to be cleared before walking guest page tables.
+	 */
+	error_code &= ~PFERR_RSVD_MASK;
+
 	/*
 	 * Look up the guest pte for the faulting address.
 	 */