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Subject[PATCH v2 3/10] KVM: MMU: fix direct sp's access corruptted
Consider using small page to fit guest's large page mapping:

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/mmu.c | 3 ++-
arch/x86/kvm/paging_tmpl.h | 18 ++++++++++++++++++
2 files changed, 20 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 556a798..0412ba4 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -153,7 +153,8 @@ module_param(oos_shadow, bool, 0644);
#define CREATE_TRACE_POINTS
#include "mmutrace.h"

-#define SPTE_HOST_WRITEABLE (1ULL << PT_FIRST_AVAIL_BITS_SHIFT)
+#define SPTE_HOST_WRITEABLE (1ULL << PT_FIRST_AVAIL_BITS_SHIFT)
+#define SPTE_NO_DIRTY (2ULL << PT_FIRST_AVAIL_BITS_SHIFT)

#define SHADOW_PT_INDEX(addr, level) PT64_INDEX(addr, level)

diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index e46eb8a..fdba751 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -325,6 +325,20 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
break;
}

+ if (*sptep & SPTE_NO_DIRTY) {
+ struct kvm_mmu_page *child;
+
+ WARN_ON(level != gw->level);
+ WARN_ON(!is_shadow_present_pte(*sptep));
+ if (dirty) {
+ child = page_header(*sptep &
+ PT64_BASE_ADDR_MASK);
+ mmu_page_remove_parent_pte(child, sptep);
+ __set_spte(sptep, shadow_trap_nonpresent_pte);
+ kvm_flush_remote_tlbs(vcpu->kvm);
+ }
+ }
+
if (is_shadow_present_pte(*sptep) && !is_large_pte(*sptep))
continue;

@@ -365,6 +379,10 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
}
}

+ if (level == gw->level && !dirty &&
+ access & gw->pte_access & ACC_WRITE_MASK)
+ spte |= SPTE_NO_DIRTY;
+
spte = __pa(sp->spt)
| PT_PRESENT_MASK | PT_ACCESSED_MASK
| PT_WRITABLE_MASK | PT_USER_MASK;
--
1.6.1.2




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