From 65855ed8b03437e79e42f2a89a993206981ac6cb Mon Sep 17 00:00:00 2001 From: Lai Jiangshan Date: Sat, 18 Sep 2021 08:56:28 +0800 Subject: [PATCH] KVM: X86: Synchronize the shadow pagetable before link it If gpte is changed from non-present to present, the guest doesn't need to flush tlb per SDM. So the host must synchronze sp before link it. Otherwise the guest might use a wrong mapping. For example: the guest first changes a level-1 pagetable, and then links its parent to a new place where the original gpte is non-present. Finally the guest can access the remapped area without flushing the tlb. The guest's behavior should be allowed per SDM, but the host kvm mmu makes it wrong. Fixes: 4731d4c7a077 ("KVM: MMU: out of sync shadow core") Signed-off-by: Lai Jiangshan Signed-off-by: Paolo Bonzini Message-Id: <20210918005636.3675-3-jiangshanlai@gmail.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/mmu/mmu.c | 17 ++++++++++------- arch/x86/kvm/mmu/paging_tmpl.h | 23 +++++++++++++++++++++-- 2 files changed, 31 insertions(+), 9 deletions(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 2d7e61122af8..1a64ba5b9437 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -2027,8 +2027,8 @@ static void mmu_pages_clear_parents(struct mmu_page_path *parents) } while (!sp->unsync_children); } -static void mmu_sync_children(struct kvm_vcpu *vcpu, - struct kvm_mmu_page *parent) +static int mmu_sync_children(struct kvm_vcpu *vcpu, + struct kvm_mmu_page *parent, bool can_yield) { int i; struct kvm_mmu_page *sp; @@ -2055,12 +2055,18 @@ static void mmu_sync_children(struct kvm_vcpu *vcpu, } if (need_resched() || rwlock_needbreak(&vcpu->kvm->mmu_lock)) { kvm_mmu_flush_or_zap(vcpu, &invalid_list, false, flush); + if (!can_yield) { + kvm_make_request(KVM_REQ_MMU_SYNC, vcpu); + return -EINTR; + } + cond_resched_rwlock_write(&vcpu->kvm->mmu_lock); flush = false; } } kvm_mmu_flush_or_zap(vcpu, &invalid_list, false, flush); + return 0; } static void __clear_sp_write_flooding_count(struct kvm_mmu_page *sp) @@ -2146,9 +2152,6 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu, kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu); } - if (sp->unsync_children) - kvm_make_request(KVM_REQ_MMU_SYNC, vcpu); - __clear_sp_write_flooding_count(sp); trace_get_page: @@ -3684,7 +3687,7 @@ void kvm_mmu_sync_roots(struct kvm_vcpu *vcpu) write_lock(&vcpu->kvm->mmu_lock); kvm_mmu_audit(vcpu, AUDIT_PRE_SYNC); - mmu_sync_children(vcpu, sp); + mmu_sync_children(vcpu, sp, true); kvm_mmu_audit(vcpu, AUDIT_POST_SYNC); write_unlock(&vcpu->kvm->mmu_lock); @@ -3700,7 +3703,7 @@ void kvm_mmu_sync_roots(struct kvm_vcpu *vcpu) if (IS_VALID_PAE_ROOT(root)) { root &= PT64_BASE_ADDR_MASK; sp = to_shadow_page(root); - mmu_sync_children(vcpu, sp); + mmu_sync_children(vcpu, sp, true); } } diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h index efce0a935e23..913d52a7923e 100644 --- a/arch/x86/kvm/mmu/paging_tmpl.h +++ b/arch/x86/kvm/mmu/paging_tmpl.h @@ -707,8 +707,27 @@ static int FNAME(fetch)(struct kvm_vcpu *vcpu, gpa_t addr, if (!is_shadow_present_pte(*it.sptep)) { table_gfn = gw->table_gfn[it.level - 2]; access = gw->pt_access[it.level - 2]; - sp = kvm_mmu_get_page(vcpu, table_gfn, addr, it.level-1, - false, access); + sp = kvm_mmu_get_page(vcpu, table_gfn, addr, + it.level-1, false, access); + /* + * We must synchronize the pagetable before linking it + * because the guest doesn't need to flush tlb when + * the gpte is changed from non-present to present. + * Otherwise, the guest may use the wrong mapping. + * + * For PG_LEVEL_4K, kvm_mmu_get_page() has already + * synchronized it transiently via kvm_sync_page(). + * + * For higher level pagetable, we synchronize it via + * the slower mmu_sync_children(). If it needs to + * break, some progress has been made; return + * RET_PF_RETRY and retry on the next #PF. + * KVM_REQ_MMU_SYNC is not necessary but it + * expedites the process. + */ + if (sp->unsync_children && + mmu_sync_children(vcpu, sp, false)) + return RET_PF_RETRY; } /* -- 2.20.1