While we sync the unsync sp, we may mapping the spte writable, it's dangerous, if one unsync sp's mapping gfn is another unsync page's gfn.
For example: have two unsync pages SP1, SP2 and: SP1.pte[0] = P SP2.gfn's pfn = P [SP1.pte[0] = SP2.gfn's pfn] First, we unsync SP2, it will write protect for SP2.gfn since SP1.pte[0] is mapping to this page, it will mark read only. Then, we unsync SP1, SP1.pte[0] may mark to writable. Now, we will write SP2.gfn by SP1.pte[0] mapping This bug will corrupt guest's page table, fixed by mark read-only mapping if the mapped gfn has shadow page Signed-off-by: Xiao Guangrong <[email protected]> --- arch/x86/kvm/mmu.c | 14 ++++---------- 1 files changed, 4 insertions(+), 10 deletions(-) diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index 045a0f9..556a798 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -1810,11 +1810,14 @@ static int mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn, bool need_unsync = false; for_each_gfn_indirect_valid_sp(vcpu->kvm, s, gfn, node) { + if (!can_unsync) + return 1; + if (s->role.level != PT_PAGE_TABLE_LEVEL) return 1; if (!need_unsync && !s->unsync) { - if (!can_unsync || !oos_shadow) + if (!oos_shadow) return 1; need_unsync = true; } @@ -1877,15 +1880,6 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep, if (!tdp_enabled && !(pte_access & ACC_WRITE_MASK)) spte &= ~PT_USER_MASK; - /* - * Optimization: for pte sync, if spte was writable the hash - * lookup is unnecessary (and expensive). Write protection - * is responsibility of mmu_get_page / kvm_sync_page. - * Same reasoning can be applied to dirty page accounting. - */ - if (!can_unsync && is_writable_pte(*sptep)) - goto set_pte; - if (mmu_need_write_protect(vcpu, gfn, can_unsync)) { pgprintk("%s: found shadow page for %lx, marking ro\n", __func__, gfn); -- 1.6.1.2 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
