From: Avi Kivity <[email protected]>
Currently, when we fetch an spte, we only verify that gptes match those that
the walker saw if we build new shadow pages for them.
However, this misses the following race:
vcpu1 vcpu2
walk
change gpte
walk
instantiate sp
fetch existing sp
Fix by validating every gpte, regardless of whether it is used for building
a new sp or not.
Signed-off-by: Avi Kivity <[email protected]>
Signed-off-by: Marcelo Tosatti <[email protected]>
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index a550957..284ab16 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -319,10 +319,11 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t
addr,
int *ptwrite, pfn_t pfn)
{
unsigned access = gw->pt_access;
- struct kvm_mmu_page *sp;
+ struct kvm_mmu_page *sp = NULL;
u64 *sptep = NULL;
int uninitialized_var(level);
bool dirty = is_dirty_gpte(gw->ptes[gw->level - 1]);
+ int top_level;
unsigned direct_access;
struct kvm_shadow_walk_iterator iterator;
@@ -333,6 +334,18 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
if (!dirty)
direct_access &= ~ACC_WRITE_MASK;
+ top_level = vcpu->arch.mmu.root_level;
+ if (top_level == PT32E_ROOT_LEVEL)
+ top_level = PT32_ROOT_LEVEL;
+ /*
+ * Verify that the top-level gpte is still there. Since the page
+ * is a root page, it is either write protected (and cannot be
+ * changed from now on) or it is invalid (in which case, we don't
+ * really care if it changes underneath us after this point).
+ */
+ if (FNAME(gpte_changed)(vcpu, gw, top_level))
+ goto out_gpte_changed;
+
for (shadow_walk_init(&iterator, vcpu, addr);
shadow_walk_okay(&iterator) && iterator.level > gw->level;
shadow_walk_next(&iterator)) {
@@ -343,12 +356,12 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t
addr,
drop_large_spte(vcpu, sptep);
- if (is_shadow_present_pte(*sptep))
- continue;
-
- table_gfn = gw->table_gfn[level - 2];
- sp = kvm_mmu_get_page(vcpu, table_gfn, addr, level-1,
- false, access, sptep);
+ sp = NULL;
+ if (!is_shadow_present_pte(*sptep)) {
+ table_gfn = gw->table_gfn[level - 2];
+ sp = kvm_mmu_get_page(vcpu, table_gfn, addr, level-1,
+ false, access, sptep);
+ }
/*
* Verify that the gpte in the page we've just write
@@ -357,7 +370,8 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
if (FNAME(gpte_changed)(vcpu, gw, level - 1))
goto out_gpte_changed;
- link_shadow_page(sptep, sp);
+ if (sp)
+ link_shadow_page(sptep, sp);
}
for (;
@@ -392,7 +406,8 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
return sptep;
out_gpte_changed:
- kvm_mmu_put_page(sp, sptep);
+ if (sp)
+ kvm_mmu_put_page(sp, sptep);
kvm_release_pfn_clean(pfn);
return NULL;
}
--
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