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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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