[PATCH v2 2/10] KVM: MMU: fix conflict access permissions in direct sp

[Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxx>]

In no-direct mapping, we mark sp is 'direct' when we mapping the
guest's larger page, but its access is encoded form upper page-struct
entire not include the last mapping, it will cause access conflict.

For example, have this mapping:
        [W] 
      / PDE1 -> |---|
  P[W]          |   | LPA
      \ PDE2 -> |---|
        [R]

P have two children, PDE1 and PDE2, both PDE1 and PDE2 mapping the
same lage page(LPA). The P's access is WR, PDE1's access is WR,
PDE2's access is RO(just consider read-write permissions here)

When guest access PDE1, we will create a direct sp for LPA, the sp's
access is from P, is W, then we will mark the ptes is W in this sp.

Then, guest access PDE2, we will find LPA's shadow page, is the same as
PDE's, and mark the ptes is RO.

So, if guest access PDE1, the incorrect #PF is occured.

Fixed by encode the last mapping access into direct shadow page

And, it also cleanup the code that directly get the last level's dirty flag

Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxx>
---
 arch/x86/kvm/paging_tmpl.h |    9 +++++----
 1 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 37c26cb..e46eb8a 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -306,6 +306,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
 	gfn_t table_gfn;
 	int r;
 	int level;
+	bool dirty = is_dirty_gpte(gw->ptes[gw->level-1]);
 	pt_element_t curr_pte;
 	struct kvm_shadow_walk_iterator iterator;
 
@@ -319,8 +320,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
 			mmu_set_spte(vcpu, sptep, access,
 				     gw->pte_access & access,
 				     user_fault, write_fault,
-				     is_dirty_gpte(gw->ptes[gw->level-1]),
-				     ptwrite, level,
+				     dirty, ptwrite, level,
 				     gw->gfn, pfn, false, true);
 			break;
 		}
@@ -335,10 +335,11 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
 		}
 
 		if (level <= gw->level) {
-			int delta = level - gw->level + 1;
 			direct = 1;
-			if (!is_dirty_gpte(gw->ptes[level - delta]))
+			if (!dirty)
 				access &= ~ACC_WRITE_MASK;
+			access &= gw->pte_access;
+
 			/*
 			 * It is a large guest pages backed by small host pages,
 			 * So we set @direct(@sp->role.direct)=1, and set
-- 
1.6.1.2



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