linux-kernel - [FYI PATCH 5/5] x86/KVM: Clean up host's steal time structure

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Date:   Thu, 30 Jan 2020 19:01:56 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        stable@...r.kernel.org
Subject: [FYI PATCH 5/5] x86/KVM: Clean up host's steal time structure

From: Boris Ostrovsky <boris.ostrovsky@...cle.com>

Now that we are mapping kvm_steal_time from the guest directly we
don't need keep a copy of it in kvm_vcpu_arch.st. The same is true
for the stime field.

This is part of CVE-2019-3016.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Reviewed-by: Joao Martins <joao.m.martins@...cle.com>
Cc: stable@...r.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/include/asm/kvm_host.h |  3 +--
 arch/x86/kvm/x86.c              | 11 +++--------
 2 files changed, 4 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index f48a306e..4925bdb 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -685,10 +685,9 @@ struct kvm_vcpu_arch {
 	bool pvclock_set_guest_stopped_request;
 
 	struct {
+		u8 preempted;
 		u64 msr_val;
 		u64 last_steal;
-		struct gfn_to_hva_cache stime;
-		struct kvm_steal_time steal;
 		struct gfn_to_pfn_cache cache;
 	} st;
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f1845df..a0381ec 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2604,7 +2604,7 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
 	if (xchg(&st->preempted, 0) & KVM_VCPU_FLUSH_TLB)
 		kvm_vcpu_flush_tlb(vcpu, false);
 
-	vcpu->arch.st.steal.preempted = 0;
+	vcpu->arch.st.preempted = 0;
 
 	if (st->version & 1)
 		st->version += 1;  /* first time write, random junk */
@@ -2788,11 +2788,6 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		if (data & KVM_STEAL_RESERVED_MASK)
 			return 1;
 
-		if (kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.st.stime,
-						data & KVM_STEAL_VALID_BITS,
-						sizeof(struct kvm_steal_time)))
-			return 1;
-
 		vcpu->arch.st.msr_val = data;
 
 		if (!(data & KVM_MSR_ENABLED))
@@ -3509,7 +3504,7 @@ static void kvm_steal_time_set_preempted(struct kvm_vcpu *vcpu)
 	if (!(vcpu->arch.st.msr_val & KVM_MSR_ENABLED))
 		return;
 
-	if (vcpu->arch.st.steal.preempted)
+	if (vcpu->arch.st.preempted)
 		return;
 
 	if (kvm_map_gfn(vcpu, vcpu->arch.st.msr_val >> PAGE_SHIFT, &map,
@@ -3519,7 +3514,7 @@ static void kvm_steal_time_set_preempted(struct kvm_vcpu *vcpu)
 	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;
+	st->preempted = vcpu->arch.st.preempted = KVM_VCPU_PREEMPTED;
 
 	kvm_unmap_gfn(vcpu, &map, &vcpu->arch.st.cache, true, true);
 }
-- 
1.8.3.1