linux-kernel - [PATCH 3/3] KVM: x86: never write to memory from kvm_vcpu_check

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Date:   Wed, 27 Apr 2022 13:37:58 -0400
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     mlevitsk@...hat.com, seanjc@...gle.com, stable@...r.kernel.org
Subject: [PATCH 3/3] KVM: x86: never write to memory from kvm_vcpu_check_block

kvm_vcpu_check_block is called while not in TASK_RUNNING, and therefore
cannot sleep.  Writing to guest memory is therefore forbidden, but it
can happen if kvm_check_nested_events causes a vmexit.

Fortunately, all events that are caught by kvm_check_nested_events are
also handled by kvm_vcpu_has_events through vendor callbacks such as
kvm_x86_interrupt_allowed or kvm_x86_ops.nested_ops->has_events, so
remove the call.

Cc: stable@...r.kernel.org
Reported-by: Maxim Levitsky <mlevitsk@...hat.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/x86.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d563812ca229..90b4f50b9a84 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10341,9 +10341,6 @@ static inline int vcpu_block(struct kvm_vcpu *vcpu)

 static inline bool kvm_vcpu_running(struct kvm_vcpu *vcpu)
 {
-	if (is_guest_mode(vcpu))
-		kvm_check_nested_events(vcpu);
-
 	return (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE &&
 		!vcpu->arch.apf.halted);
 }
-- 
2.31.1