KVM: MMU: Make cmpxchg_gpte aware of nesting too

This patch makes the cmpxchg_gpte() function aware of the
difference between l1-gfns and l2-gfns when nested
virtualization is in use.  This fixes a potential
data-corruption problem in the l1-guest and makes the code
work correct (at least as correct as the hardware which is
emulated in this code) again.

Cc: stable@kernel.org
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 23 insertions, 7 deletions

diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 74f8567d57ac..1b6899088f97 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -78,15 +78,21 @@ static gfn_t gpte_to_gfn_lvl(pt_element_t gpte, int lvl)
         return (gpte & PT_LVL_ADDR_MASK(lvl)) >> PAGE_SHIFT;
 }
 
-static bool FNAME(cmpxchg_gpte)(struct kvm *kvm,
+static int FNAME(cmpxchg_gpte)(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
                          gfn_t table_gfn, unsigned index,
                          pt_element_t orig_pte, pt_element_t new_pte)
 {
         pt_element_t ret;
         pt_element_t *table;
         struct page *page;
+        gpa_t gpa;
 
-        page = gfn_to_page(kvm, table_gfn);
+        gpa = mmu->translate_gpa(vcpu, table_gfn << PAGE_SHIFT,
+                                 PFERR_USER_MASK|PFERR_WRITE_MASK);
+        if (gpa == UNMAPPED_GVA)
+                return -EFAULT;
+
+        page = gfn_to_page(vcpu->kvm, gpa_to_gfn(gpa));
 
         table = kmap_atomic(page, KM_USER0);
         ret = CMPXCHG(&table[index], orig_pte, new_pte);
@@ -192,11 +198,17 @@ walk:
 #endif
 
                 if (!eperm && !rsvd_fault && !(pte & PT_ACCESSED_MASK)) {
+                        int ret;
                         trace_kvm_mmu_set_accessed_bit(table_gfn, index,
                                                        sizeof(pte));
-                        if (FNAME(cmpxchg_gpte)(vcpu->kvm, table_gfn,
-                            index, pte, pte|PT_ACCESSED_MASK))
+                        ret = FNAME(cmpxchg_gpte)(vcpu, mmu, table_gfn,
+                                        index, pte, pte|PT_ACCESSED_MASK);
+                        if (ret < 0) {
+                                present = false;
+                                break;
+                        } else if (ret)
                                 goto walk;
+
                         mark_page_dirty(vcpu->kvm, table_gfn);
                         pte |= PT_ACCESSED_MASK;
                 }
@@ -245,13 +257,17 @@ walk:
                 goto error;
 
         if (write_fault && !is_dirty_gpte(pte)) {
-                bool ret;
+                int ret;
 
                 trace_kvm_mmu_set_dirty_bit(table_gfn, index, sizeof(pte));
-                ret = FNAME(cmpxchg_gpte)(vcpu->kvm, table_gfn, index, pte,
+                ret = FNAME(cmpxchg_gpte)(vcpu, mmu, table_gfn, index, pte,
                             pte|PT_DIRTY_MASK);
-                if (ret)
+                if (ret < 0) {
+                        present = false;
+                        goto error;
+                } else if (ret)
                         goto walk;
+
                 mark_page_dirty(vcpu->kvm, table_gfn);
                 pte |= PT_DIRTY_MASK;
                 walker->ptes[walker->level - 1] = pte;