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Mon, 27 Jul 2026 15:02:55 +0000 (GMT) Received: from p-imbrenda.ibmuc.com (unknown [9.111.1.146]) by smtpav06.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 27 Jul 2026 15:02:55 +0000 (GMT) From: Claudio Imbrenda To: linux-kernel@vger.kernel.org Cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org, borntraeger@de.ibm.com, frankja@linux.ibm.com, david@kernel.org, seiden@linux.ibm.com, nrb@linux.ibm.com, schlameuss@linux.ibm.com, gra@linux.ibm.com Subject: [PATCH v3 01/10] KVM: s390: Fix unlikely NULL gmap dereference Date: Mon, 27 Jul 2026 17:02:45 +0200 Message-ID: <20260727150254.236021-2-imbrenda@linux.ibm.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260727150254.236021-1-imbrenda@linux.ibm.com> References: <20260727150254.236021-1-imbrenda@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Info: AW1haW4tMjYwNzI3MDE0MCBTYWx0ZWRfX/Rt0RWBVE2S5 MVmNAFidP/TRuc5pjBQDSMhAAdRgy72ow/iS0Q+4uSlMtPjbvaLPjb2ckYtLZ2eYr5Yk0o/8Yae hNHws7FtDKERC3KVHo+v1O02NPbpsCs= X-Proofpoint-GUID: JC4gK2GWBH3bKM8vw8XIjlZuozd04YaW X-Proofpoint-ORIG-GUID: JC4gK2GWBH3bKM8vw8XIjlZuozd04YaW X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzI3MDE0MCBTYWx0ZWRfXzjejP3lpLKXs ToKKDEYZYQ12PL+IQ5isGwZvm+tLR2gfBVyhj4v/0X+BG5hNaHTzm9ozq4DCUjxy8a3ul9C+/30 pVUE8J+8kELB3pwj2hGQHGfpz25WnDKCpin5SRX9z3PiNPG8Ab1vNmdn6g1t/2IF4dKnZ11a+VW 2Sd3lNbWpCLGLtaBsiTLNxMg9VyOeJnS3nq4Q6+FHalasNrpwTtg2+oF5TJmoSfKcO05so7qiGL YibLkVgA85UYc9GeVZWSePHlBaWt7+Azmt01ahg9xGa/2bvg3JeXQMtZHgN05LBKozZwPWd2Qsj axslPZfihibWkafQv26YtGHcv+59eeM3Mn/69rkMEBL1oaACml0KiwvfhnWMPiNq6XGEd/IpaPe deSMYZLdY0SfM8Q+Fqbb+iDSKwGnf+NIsmE/Agx0AqxKHqbpNtvXRXa+DQU0r/iJ1eoLwIuFK0e 9tAVUrctwhVEtSAT3+w== X-Authority-Analysis: v=2.4 cv=X5Vi7mTe c=1 sm=1 tr=0 ts=6a677327 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=VnNF1IyMAAAA:8 a=-aBWQn_vEbd_VLME6SsA:9 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-07-27_04,2026-07-24_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 impostorscore=0 lowpriorityscore=0 phishscore=0 priorityscore=1501 malwarescore=0 spamscore=0 suspectscore=0 bulkscore=0 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607270140 When creating a new vCPU, kvm_vm_ioctl_create_vcpu() will call kvm_arch_vcpu_postcreate() after the file descriptor for the new vCPU has been created. The new file descriptor has not been returned yet, but a malicious userspace program could try to guess it. If a malicious userspace program manages to start the newly created vCPU before kvm_arch_vcpu_postcreate() is called, __vcpu_run() will try to dereference vcpu->arch.gmap and trigger a NULL pointer dereference. Fix this by adding a new field to struct kvm_vcpu_arch to keep track of the initialization status of the vCPU. Refuse to run a vCPU that is not fully initialized. Fixes: dafd032a15f8 ("KVM: s390: move vcpu specific initalization to a later point") Fixes: e38c884df921 ("KVM: s390: Switch to new gmap") Signed-off-by: Claudio Imbrenda Reviewed-by: Steffen Eiden --- arch/s390/include/asm/kvm_host.h | 1 + arch/s390/kvm/kvm-s390.c | 8 ++++++++ 2 files changed, 9 insertions(+) diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h index eaa34c5bd3c1..edf75b6ad20c 100644 --- a/arch/s390/include/asm/kvm_host.h +++ b/arch/s390/include/asm/kvm_host.h @@ -440,6 +440,7 @@ struct kvm_vcpu_arch { bool skey_enabled; /* Indicator if the access registers have been loaded from guest */ bool acrs_loaded; + bool initialized; struct kvm_s390_pv_vcpu pv; union diag318_info diag318_info; struct kvm_s390_mmu_cache *mc; diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 150b5dd2170e..22535f76ae05 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -3613,6 +3613,8 @@ void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu) if (test_kvm_facility(vcpu->kvm, 74) || vcpu->kvm->arch.user_instr0 || vcpu->kvm->arch.user_operexec) vcpu->arch.sie_block->ictl |= ICTL_OPEREXC; + + WRITE_ONCE(vcpu->arch.initialized, true); } static bool kvm_has_pckmo_subfunc(struct kvm *kvm, unsigned long nr) @@ -5039,6 +5041,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) kvm_run->kvm_dirty_regs & ~KVM_SYNC_S390_VALID_FIELDS) return -EINVAL; + if (!READ_ONCE(vcpu->arch.initialized)) + return -EINVAL; + vcpu_load(vcpu); if (guestdbg_exit_pending(vcpu)) { @@ -5523,6 +5528,9 @@ long kvm_arch_vcpu_ioctl(struct file *filp, long r; u16 rc, rrc; + if (!READ_ONCE(vcpu->arch.initialized)) + return -EINVAL; + vcpu_load(vcpu); switch (ioctl) { -- 2.55.0