From d4074324b07a94a1fca476d452dfbb3a4e7bf656 Mon Sep 17 00:00:00 2001 From: Claudio Imbrenda Date: Mon, 20 Sep 2021 15:24:50 +0200 Subject: [PATCH] KVM: s390: pv: avoid double free of sida page If kvm_s390_pv_destroy_cpu is called more than once, we risk calling free_page on a random page, since the sidad field is aliased with the gbea, which is not guaranteed to be zero. This can happen, for example, if userspace calls the KVM_PV_DISABLE IOCTL, and it fails, and then userspace calls the same IOCTL again. This scenario is only possible if KVM has some serious bug or if the hardware is broken. The solution is to simply return successfully immediately if the vCPU was already non secure. Signed-off-by: Claudio Imbrenda Fixes: 19e1227768863a1469797c13ef8fea1af7beac2c ("KVM: S390: protvirt: Introduce instruction data area bounce buffer") Reviewed-by: Janosch Frank Reviewed-by: Christian Borntraeger Message-Id: <20210920132502.36111-3-imbrenda@linux.ibm.com> Signed-off-by: Janosch Frank Signed-off-by: Christian Borntraeger --- arch/s390/kvm/pv.c | 19 +++++++++---------- 1 file changed, 9 insertions(+), 10 deletions(-) diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c index c8841f4..0a85411 100644 --- a/arch/s390/kvm/pv.c +++ b/arch/s390/kvm/pv.c @@ -16,18 +16,17 @@ int kvm_s390_pv_destroy_cpu(struct kvm_vcpu *vcpu, u16 *rc, u16 *rrc) { - int cc = 0; + int cc; - if (kvm_s390_pv_cpu_get_handle(vcpu)) { - cc = uv_cmd_nodata(kvm_s390_pv_cpu_get_handle(vcpu), - UVC_CMD_DESTROY_SEC_CPU, rc, rrc); + if (!kvm_s390_pv_cpu_get_handle(vcpu)) + return 0; + + cc = uv_cmd_nodata(kvm_s390_pv_cpu_get_handle(vcpu), UVC_CMD_DESTROY_SEC_CPU, rc, rrc); + + KVM_UV_EVENT(vcpu->kvm, 3, "PROTVIRT DESTROY VCPU %d: rc %x rrc %x", + vcpu->vcpu_id, *rc, *rrc); + WARN_ONCE(cc, "protvirt destroy cpu failed rc %x rrc %x", *rc, *rrc); - KVM_UV_EVENT(vcpu->kvm, 3, - "PROTVIRT DESTROY VCPU %d: rc %x rrc %x", - vcpu->vcpu_id, *rc, *rrc); - WARN_ONCE(cc, "protvirt destroy cpu failed rc %x rrc %x", - *rc, *rrc); - } /* Intended memory leak for something that should never happen. */ if (!cc) free_pages(vcpu->arch.pv.stor_base, -- 2.7.4