Commit 26844fee authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

KVM: x86: never write to memory from kvm_vcpu_check_block() 



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

Fortunately, all events that are caught by kvm_check_nested_events() are
also recognized 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 and postpone the actual processing to vcpu_block().

Opportunistically honor the return of kvm_check_nested_events().  KVM
punted on the check in kvm_vcpu_running() because the only error path is
if vmx_complete_nested_posted_interrupt() fails, in which case KVM exits
to userspace with "internal error" i.e. the VM is likely dead anyways so
it wasn't worth overloading the return of kvm_vcpu_running().

Add the check mostly so that KVM is consistent with itself; the return of
the call via kvm_apic_accept_events()=>kvm_check_nested_events() that
immediately follows  _is_ checked.

Reported-by: default avatarMaxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
[sean: check and handle return of kvm_check_nested_events()]
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20220921003201.1441511-11-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 1e17a6f8

arch/x86/kvm/x86.c

+11 −3
Original line number Diff line number Diff line
@@ -10817,6 +10817,17 @@ static inline int vcpu_block(struct kvm_vcpu *vcpu) 
			return 1;

	}



	/*

	 * Evaluate nested events before exiting the halted state.  This allows

	 * the halt state to be recorded properly in the VMCS12's activity

	 * state field (AMD does not have a similar field and a VM-Exit always

	 * causes a spurious wakeup from HLT).

	 */

	if (is_guest_mode(vcpu)) {

		if (kvm_check_nested_events(vcpu) < 0)

			return 0;

	}



	if (kvm_apic_accept_events(vcpu) < 0)

		return 0;

	switch(vcpu->arch.mp_state) {
@@ -10839,9 +10850,6 @@ 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);

}