126 lines
4.2 KiB
Diff
126 lines
4.2 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
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Date: Fri, 31 Jan 2020 08:06:43 -0300
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Subject: [PATCH] x86/KVM: Make sure KVM_VCPU_FLUSH_TLB flag is not missed
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CVE-2019-3016
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CVE-2020-3016
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There is a potential race in record_steal_time() between setting
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host-local vcpu->arch.st.steal.preempted to zero (i.e. clearing
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KVM_VCPU_PREEMPTED) and propagating this value to the guest with
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kvm_write_guest_cached(). Between those two events the guest may
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still see KVM_VCPU_PREEMPTED in its copy of kvm_steal_time, set
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KVM_VCPU_FLUSH_TLB and assume that hypervisor will do the right
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thing. Which it won't.
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Instad of copying, we should map kvm_steal_time and that will
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guarantee atomicity of accesses to @preempted.
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This is part of CVE-2019-3016.
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Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
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Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
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Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
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Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
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---
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arch/x86/kvm/x86.c | 49 +++++++++++++++++++++++++++-------------------
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1 file changed, 29 insertions(+), 20 deletions(-)
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diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
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index 41fee3d359ab..431e34965707 100644
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--- a/arch/x86/kvm/x86.c
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+++ b/arch/x86/kvm/x86.c
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@@ -2482,43 +2482,45 @@ static void kvm_vcpu_flush_tlb(struct kvm_vcpu *vcpu, bool invalidate_gpa)
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static void record_steal_time(struct kvm_vcpu *vcpu)
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{
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+ struct kvm_host_map map;
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+ struct kvm_steal_time *st;
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+
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if (!(vcpu->arch.st.msr_val & KVM_MSR_ENABLED))
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return;
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- if (unlikely(kvm_read_guest_cached(vcpu->kvm, &vcpu->arch.st.stime,
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- &vcpu->arch.st.steal, sizeof(struct kvm_steal_time))))
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+ /* -EAGAIN is returned in atomic context so we can just return. */
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+ if (kvm_map_gfn(vcpu, vcpu->arch.st.msr_val >> PAGE_SHIFT,
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+ &map, &vcpu->arch.st.cache, false))
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return;
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+ st = map.hva +
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+ offset_in_page(vcpu->arch.st.msr_val & KVM_STEAL_VALID_BITS);
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+
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/*
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* Doing a TLB flush here, on the guest's behalf, can avoid
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* expensive IPIs.
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*/
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- if (xchg(&vcpu->arch.st.steal.preempted, 0) & KVM_VCPU_FLUSH_TLB)
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+ if (xchg(&st->preempted, 0) & KVM_VCPU_FLUSH_TLB)
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kvm_vcpu_flush_tlb(vcpu, false);
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- if (vcpu->arch.st.steal.version & 1)
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- vcpu->arch.st.steal.version += 1; /* first time write, random junk */
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+ vcpu->arch.st.steal.preempted = 0;
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- vcpu->arch.st.steal.version += 1;
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+ if (st->version & 1)
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+ st->version += 1; /* first time write, random junk */
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- kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.st.stime,
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- &vcpu->arch.st.steal, sizeof(struct kvm_steal_time));
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+ st->version += 1;
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smp_wmb();
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- vcpu->arch.st.steal.steal += current->sched_info.run_delay -
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+ st->steal += current->sched_info.run_delay -
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vcpu->arch.st.last_steal;
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vcpu->arch.st.last_steal = current->sched_info.run_delay;
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- kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.st.stime,
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- &vcpu->arch.st.steal, sizeof(struct kvm_steal_time));
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-
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smp_wmb();
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- vcpu->arch.st.steal.version += 1;
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+ st->version += 1;
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- kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.st.stime,
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- &vcpu->arch.st.steal, sizeof(struct kvm_steal_time));
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+ kvm_unmap_gfn(vcpu, &map, &vcpu->arch.st.cache, true, false);
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}
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int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
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@@ -3390,18 +3392,25 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
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static void kvm_steal_time_set_preempted(struct kvm_vcpu *vcpu)
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{
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+ struct kvm_host_map map;
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+ struct kvm_steal_time *st;
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+
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if (!(vcpu->arch.st.msr_val & KVM_MSR_ENABLED))
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return;
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if (vcpu->arch.st.steal.preempted)
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return;
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- vcpu->arch.st.steal.preempted = KVM_VCPU_PREEMPTED;
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+ if (kvm_map_gfn(vcpu, vcpu->arch.st.msr_val >> PAGE_SHIFT, &map,
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+ &vcpu->arch.st.cache, true))
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+ return;
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+
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+ st = map.hva +
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+ offset_in_page(vcpu->arch.st.msr_val & KVM_STEAL_VALID_BITS);
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+
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+ st->preempted = vcpu->arch.st.steal.preempted = KVM_VCPU_PREEMPTED;
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- kvm_write_guest_offset_cached(vcpu->kvm, &vcpu->arch.st.stime,
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- &vcpu->arch.st.steal.preempted,
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- offsetof(struct kvm_steal_time, preempted),
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- sizeof(vcpu->arch.st.steal.preempted));
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+ kvm_unmap_gfn(vcpu, &map, &vcpu->arch.st.cache, true, true);
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}
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void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
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