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Thu, 2 Jul 2026 15:24:09 +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 v1 2/8] KVM: s390: Fix unlikely NULL gmap dereference Date: Thu, 2 Jul 2026 17:24:00 +0200 Message-ID: <20260702152406.204782-3-imbrenda@linux.ibm.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260702152406.204782-1-imbrenda@linux.ibm.com> References: <20260702152406.204782-1-imbrenda@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@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-Details-Enc: AW1haW4tMjYwNzAyMDE2MCBTYWx0ZWRfX2zsYfYJKYL45 8J0JsgCNiHuGVVD5brE6oSMe/tBCv8BpdQVc5nNXq9VUkwlGOrW0ZTVX7UQxSC1I7lmTFfDZ8hm 6xnMdpg4gRcF6/YGcjhseajUOlKjrN2aaSpavdAky2n177pH3XSZTeXQplIPV9GqNHuhdfDmALa lu/6cWOCoMua1fifB9EWSbIc3tz4xDp0ub+lZzV0TH7EEyS2Qgd+iAWXfgnwg5W84JBsLY33mNq kvFUNAAH1JYaKETnHtE1Dft9e4ell13cTuePyluYh/iTxDi5FqfqHQh9XHNKPCmg+zyOYUJWaJi 8+cleIqBcMfHyJ5CzbllOghisD1Bw6fZuO5SONCn1y+2ReFY5puv4dS3eCFjFbonyVPf7prufpf RpS4Bhlu/nU1qXedjacWv71MouL13UyZs38DSW6shkn4BNzMJTAdwuvWLbRAANOmQijhNWOhfnj 3lZtawl2S5ocTj+igwQ== X-Proofpoint-Spam-Info: AW1haW4tMjYwNzAyMDE2MCBTYWx0ZWRfX3Ta/nyuABKOh U6OFkaNHp9P8AHw1jqiAC6gbRtIVWT7TjqUBDMABoWLGWXQXoyfUw05nXnKi4DeMf4eZ9ORyL9S tfpAsrudnYgoy/KwAqwG8itIWDOxNWU= X-Proofpoint-GUID: 0zTI2uKWSvrchTUyhFuT8qmyaBEQ9EYD X-Proofpoint-ORIG-GUID: 0zTI2uKWSvrchTUyhFuT8qmyaBEQ9EYD X-Authority-Analysis: v=2.4 cv=WZ88rUhX c=1 sm=1 tr=0 ts=6a4682a0 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=VnNF1IyMAAAA:8 a=gM4Du8xaWekBHLCPAVwA:9 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-07-02_02,2026-06-26_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 adultscore=0 phishscore=0 clxscore=1015 bulkscore=0 impostorscore=0 priorityscore=1501 lowpriorityscore=0 suspectscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607020160 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 moving the initialization of vcpu->arch.gmap into kvm_arch_vcpu_create(), which is called before the file descriptor for the vCPU is created. 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 --- arch/s390/kvm/kvm-s390.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 23c817595e28..4a6d903e3523 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -3604,10 +3604,8 @@ void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu) vcpu->arch.sie_block->epdx = vcpu->kvm->arch.epdx; preempt_enable(); mutex_unlock(&vcpu->kvm->lock); - if (!kvm_is_ucontrol(vcpu->kvm)) { - vcpu->arch.gmap = vcpu->kvm->arch.gmap; + if (!kvm_is_ucontrol(vcpu->kvm)) sca_add_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; @@ -3850,6 +3848,8 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu) vcpu->arch.gmap = gmap_new_child(vcpu->kvm->arch.gmap, -1UL); if (!vcpu->arch.gmap) goto out_free_sie_block; + } else { + vcpu->arch.gmap = vcpu->kvm->arch.gmap; } VM_EVENT(vcpu->kvm, 3, "create cpu %d at 0x%p, sie block at 0x%p", -- 2.55.0