[PATCH v2 22/28] KVM: x86/mmu: Issue memory fault exit if walk failed due to memory attribute

[Paolo Bonzini <pbonzini@redhat.com>]

From: Nicolas Saenz Julienne <nsaenz@amazon.com>

During execution, page table entries are subject to memory protection
simply because their GPA is obtained with an EPT walk.  During emulation,
the checks need to be done by hand and result in an -EFAULT userspace
exit.

Signed-off-by: Nicolas Saenz Julienne <nsaenz@amazon.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/mmu/paging_tmpl.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index b031123fcb36..d2836a327bc9 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -89,6 +89,7 @@ struct guest_walker {
 	unsigned int pt_access[PT_MAX_FULL_LEVELS];
 	unsigned int pte_access;
 	gfn_t gfn;
+	bool memory_attributes_fault;
 	struct x86_exception fault;
 };
 
@@ -342,6 +343,7 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
 
 	trace_kvm_mmu_pagetable_walk(addr, access);
 retry_walk:
+	walker->memory_attributes_fault = false;
 	walker->level = w->cpu_role.base.level;
 	pte           = kvm_mmu_get_guest_pgd(vcpu, w);
 	have_ad       = PT_HAVE_ACCESSED_DIRTY(w);
@@ -411,6 +413,12 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
 		if (unlikely(kvm_is_error_hva(host_addr)))
 			goto error;
 
+		if (!kvm_mem_attributes_may_read_gfn(vcpu->kvm, gpa_to_gfn(real_gpa))) {
+			walker->memory_attributes_fault = true;
+			walker->gfn = gpa_to_gfn(real_gpa);
+			goto error;
+		}
+
 		ptep_user = (pt_element_t __user *)((void *)host_addr + offset);
 		if (unlikely(get_user(pte, ptep_user)))
 			goto error;
@@ -820,6 +828,12 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
 	 * The page is not mapped by the guest.  Let the guest handle it.
 	 */
 	if (!r) {
+		if (walker.memory_attributes_fault) {
+			fault->gfn = walker.gfn;
+			kvm_mmu_prepare_memory_fault_exit(vcpu, fault);
+			return -EFAULT;
+		}
+
 		if (!fault->prefetch)
 			__kvm_inject_emulated_page_fault(vcpu, &walker.fault, true);
 
-- 
2.52.0