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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: 4731d4c7a0 ("KVM: MMU: out of sync shadow core")
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210918005636.3675-3-jiangshanlai@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Lai Jiangshan 2021-09-18 08:56:28 +08:00 committed by Paolo Bonzini
parent f81602958c
commit 65855ed8b0
2 changed files with 31 additions and 9 deletions
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17
arch/x86/kvm/mmu/mmu.c
View File

@ -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);
}
}

23
arch/x86/kvm/mmu/paging_tmpl.h
View File

@ -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;
}
/*