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KVM: MMU: Validate all gptes during fetch, not just those used for new pages

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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 <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Avi Kivity 2010-07-13 14:27:10 +03:00
parent 0b3c933302
commit 5991b33237
1 changed files with 24 additions and 9 deletions
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33
arch/x86/kvm/paging_tmpl.h
View File

@ -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;
}