From: Paolo Bonzini <pbonzini@redhat.com>
To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>, stable@vger.kernel.org
Subject: [FYI PATCH 4/5] x86/KVM: Make sure KVM_VCPU_FLUSH_TLB flag is not missed
Date: Thu, 30 Jan 2020 19:01:55 +0100 [thread overview]
Message-ID: <1580407316-11391-5-git-send-email-pbonzini@redhat.com> (raw)
In-Reply-To: <1580407316-11391-1-git-send-email-pbonzini@redhat.com>
From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
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>
---
arch/x86/kvm/x86.c | 51 ++++++++++++++++++++++++++++++---------------------
1 file changed, 30 insertions(+), 21 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0795bc8..f1845df 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2581,45 +2581,47 @@ 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)
@@ -3501,18 +3503,25 @@ 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)
--
1.8.3.1
next prev parent reply other threads:[~2020-01-30 18:02 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-30 18:01 [FYI PATCH 0/5] Missing TLB flushes Paolo Bonzini
2020-01-30 18:01 ` [FYI PATCH 1/5] x86/kvm: Be careful not to clear KVM_VCPU_FLUSH_TLB bit Paolo Bonzini
2020-01-30 18:01 ` [FYI PATCH 2/5] x86/kvm: Introduce kvm_(un)map_gfn() Paolo Bonzini
2020-01-30 18:01 ` [FYI PATCH 3/5] x86/kvm: Cache gfn to pfn translation Paolo Bonzini
2020-01-30 18:01 ` Paolo Bonzini [this message]
2020-01-30 18:01 ` [FYI PATCH 5/5] x86/KVM: Clean up host's steal time structure Paolo Bonzini
2020-02-01 5:53 ` [FYI PATCH 0/5] Missing TLB flushes Wanpeng Li
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