blob: d573bbfc8c3f68f6e2dcba56d1585e11cd71c8df [file] [log] [blame]
From 0a88627c9c2912f2ff82f64c86b8cf00fed13957 Mon Sep 17 00:00:00 2001
From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Date: Thu, 5 Dec 2019 03:45:32 +0000
Subject: [PATCH] x86/KVM: Make sure KVM_VCPU_FLUSH_TLB flag is not missed
commit b043138246a41064527cf019a3d51d9f015e9796 upstream.
There is a potential race in record_steal_time() between setting
host-local vcpu->arch.st.steal.preempted to zero (i.e. clearing
KVM_VCPU_PREEMPTED) and propagating this value to the guest with
kvm_write_guest_cached(). Between those two events the guest may
still see KVM_VCPU_PREEMPTED in its copy of kvm_steal_time, set
KVM_VCPU_FLUSH_TLB and assume that hypervisor will do the right
thing. Which it won't.
Instad of copying, we should map kvm_steal_time and that will
guarantee atomicity of accesses to @preempted.
This is part of CVE-2019-3016.
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0449ca02f227..a35d662fd71c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2472,45 +2472,47 @@ static void kvm_vcpu_flush_tlb(struct kvm_vcpu *vcpu, bool invalidate_gpa)
static void record_steal_time(struct kvm_vcpu *vcpu)
{
+ struct kvm_host_map map;
+ struct kvm_steal_time *st;
+
if (!(vcpu->arch.st.msr_val & KVM_MSR_ENABLED))
return;
- if (unlikely(kvm_read_guest_cached(vcpu->kvm, &vcpu->arch.st.stime,
- &vcpu->arch.st.steal, sizeof(struct kvm_steal_time))))
+ /* -EAGAIN is returned in atomic context so we can just return. */
+ if (kvm_map_gfn(vcpu, vcpu->arch.st.msr_val >> PAGE_SHIFT,
+ &map, &vcpu->arch.st.cache, false))
return;
+ st = map.hva +
+ offset_in_page(vcpu->arch.st.msr_val & KVM_STEAL_VALID_BITS);
+
/*
* Doing a TLB flush here, on the guest's behalf, can avoid
* expensive IPIs.
*/
trace_kvm_pv_tlb_flush(vcpu->vcpu_id,
- vcpu->arch.st.steal.preempted & KVM_VCPU_FLUSH_TLB);
- if (xchg(&vcpu->arch.st.steal.preempted, 0) & KVM_VCPU_FLUSH_TLB)
+ st->preempted & KVM_VCPU_FLUSH_TLB);
+ if (xchg(&st->preempted, 0) & KVM_VCPU_FLUSH_TLB)
kvm_vcpu_flush_tlb(vcpu, false);
- if (vcpu->arch.st.steal.version & 1)
- vcpu->arch.st.steal.version += 1; /* first time write, random junk */
+ vcpu->arch.st.steal.preempted = 0;
- vcpu->arch.st.steal.version += 1;
+ if (st->version & 1)
+ st->version += 1; /* first time write, random junk */
- kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.st.stime,
- &vcpu->arch.st.steal, sizeof(struct kvm_steal_time));
+ st->version += 1;
smp_wmb();
- vcpu->arch.st.steal.steal += current->sched_info.run_delay -
+ st->steal += current->sched_info.run_delay -
vcpu->arch.st.last_steal;
vcpu->arch.st.last_steal = current->sched_info.run_delay;
- kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.st.stime,
- &vcpu->arch.st.steal, sizeof(struct kvm_steal_time));
-
smp_wmb();
- vcpu->arch.st.steal.version += 1;
+ st->version += 1;
- kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.st.stime,
- &vcpu->arch.st.steal, sizeof(struct kvm_steal_time));
+ kvm_unmap_gfn(vcpu, &map, &vcpu->arch.st.cache, true, false);
}
int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
@@ -3355,18 +3357,25 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
static void kvm_steal_time_set_preempted(struct kvm_vcpu *vcpu)
{
+ struct kvm_host_map map;
+ struct kvm_steal_time *st;
+
if (!(vcpu->arch.st.msr_val & KVM_MSR_ENABLED))
return;
if (vcpu->arch.st.steal.preempted)
return;
- vcpu->arch.st.steal.preempted = KVM_VCPU_PREEMPTED;
+ if (kvm_map_gfn(vcpu, vcpu->arch.st.msr_val >> PAGE_SHIFT, &map,
+ &vcpu->arch.st.cache, true))
+ return;
+
+ st = map.hva +
+ offset_in_page(vcpu->arch.st.msr_val & KVM_STEAL_VALID_BITS);
+
+ st->preempted = vcpu->arch.st.steal.preempted = KVM_VCPU_PREEMPTED;
- kvm_write_guest_offset_cached(vcpu->kvm, &vcpu->arch.st.stime,
- &vcpu->arch.st.steal.preempted,
- offsetof(struct kvm_steal_time, preempted),
- sizeof(vcpu->arch.st.steal.preempted));
+ kvm_unmap_gfn(vcpu, &map, &vcpu->arch.st.cache, true, true);
}
void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
--
2.7.4