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Subject[PATCH v3 3/11] KVM: MMU: fix direct sp's access corruptted
If the mapping is writable but the dirty flag is not set, we will find
the read-only direct sp and setup the mapping, then if the write #PF
occur, we will mark this mapping writable in the read-only direct sp,
now, other real read-only mapping will happily write it without #PF.

It may hurt guest's COW

Fixed by re-install the mapping when write #PF occur.

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
---
arch/x86/kvm/paging_tmpl.h | 28 ++++++++++++++++++++++++++--
1 files changed, 26 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 28c8493..f28f09d 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -325,8 +325,32 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
break;
}

- if (is_shadow_present_pte(*sptep) && !is_large_pte(*sptep))
- continue;
+ if (is_shadow_present_pte(*sptep) && !is_large_pte(*sptep)) {
+ struct kvm_mmu_page *child;
+ unsigned direct_access;
+
+ if (level != gw->level)
+ continue;
+
+ /*
+ * For the direct sp, if the guest pte's dirty bit
+ * changed form clean to dirty, it will corrupt the
+ * sp's access: allow writable in the read-only sp,
+ * so we should update the spte at this point to get
+ * a new sp with the correct access.
+ */
+ direct_access = gw->pt_access & gw->pte_access;
+ if (!is_dirty_gpte(gw->ptes[gw->level - 1]))
+ direct_access &= ~ACC_WRITE_MASK;
+
+ child = page_header(*sptep & PT64_BASE_ADDR_MASK);
+ if (child->role.access == direct_access)
+ continue;
+
+ mmu_page_remove_parent_pte(child, sptep);
+ __set_spte(sptep, shadow_trap_nonpresent_pte);
+ kvm_flush_remote_tlbs(vcpu->kvm);
+ }

if (is_large_pte(*sptep)) {
rmap_remove(vcpu->kvm, sptep);
--
1.6.1.2



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