From 36a2e6774bfb5f32a0f23bb155f1f960321f291b Mon Sep 17 00:00:00 2001 From: Xiao Guangrong Date: Wed, 30 Jun 2010 16:02:02 +0800 Subject: [PATCH] KVM: MMU: fix writable sync sp mapping While we sync many unsync sp at one time(in mmu_sync_children()), we may mapping the spte writable, it's dangerous, if one unsync sp's mapping gfn is another unsync page's gfn. For example: SP1.pte[0] = P SP2.gfn's pfn = P [SP1.pte[0] = SP2.gfn's pfn] First, we write protected SP1 and SP2, but SP1 and SP2 are still the unsync sp. Then, sync SP1 first, it will detect SP1.pte[0].gfn only has one unsync-sp, that is SP2, so it will mapping it writable, but we plan to sync SP2 soon, at this point, the SP2->unsync is not reliable since later we sync SP2 but SP2->gfn is already writable. So the final result is: SP2 is the sync page but SP2.gfn is writable. This bug will corrupt guest's page table, fixed by mark read-only mapping if the mapped gfn has shadow pages. Signed-off-by: Xiao Guangrong Signed-off-by: Marcelo Tosatti --- arch/x86/kvm/mmu.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index 690a7fc58c1..ca07ed083b5 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; } -- 2.20.1