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Mon, 13 Jul 2026 15:08:58 +0000 (GMT) Received: from p-imbrenda.ibmuc.com (unknown [9.87.153.197]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 13 Jul 2026 15:08:58 +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 v2 1/7] KVM: s390: Fix unlikely NULL gmap dereference Date: Mon, 13 Jul 2026 17:08:51 +0200 Message-ID: <20260713150857.269954-2-imbrenda@linux.ibm.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260713150857.269954-1-imbrenda@linux.ibm.com> References: <20260713150857.269954-1-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-GUID: cP-Q-t-SwB4YIUSebqxwgS7hBDCBP0mR X-Proofpoint-Spam-Info: AW1haW4tMjYwNzEzMDE1MyBTYWx0ZWRfX1cIws3gTjnBr efHVVqSX4K05xvj7zwX9v5Aze4w05w+cP93krNCF1nwfk6YcxmDuOTit1lIx3ILx3DtlaJc7vwW Rw9nREGeqIQXiOjmEhYwPpW5rkZkf3w= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzEzMDE1MyBTYWx0ZWRfX3vFFZ/c5nAUy kHWZ8Occ9YBKsOQF7d/sFgPwQ2FOyDTQUNd/cxFtxrzxat/Lrl5QB72DGGm5KOna1E+U2CWyKw+ //V/3VwKxH+JloZO626kxWMdYc0V/93RquBQDLIDnNJW+xwT8g4vvws3cbBceNSGBiSGT4WA72G PH6bh2teNVibXkmfJHbVkwgu84ZrZsoka+OabeJUwiPtSSoYbqkvm/Od5XMSq39osy43DCiUWsd 7jArt9Px0Oyx+luyLVZ5FJ2UnfT8U6So6YWQsWQTR1AqdkurN5ZPf19Cnp0SS5VpSvIYi2fh+ja smQTjgxfQRzaz+TwOqQATrZ8Hg/LcLAkY28bJW4SK4YqVScfmewflDgp6tee5YJr6ZRPDCMANFV O+mNp6n0brsGBA5CsrSKZaftczqTZGpYW/CJpj1JG0HwlqlJ3/vD6MeHoeeTQY5hbDoZOExibp5 toV4lBQqyVCW4F0arZQ== X-Authority-Analysis: v=2.4 cv=XbS5Co55 c=1 sm=1 tr=0 ts=6a54ff92 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=VnNF1IyMAAAA:8 a=-aBWQn_vEbd_VLME6SsA:9 X-Proofpoint-ORIG-GUID: cP-Q-t-SwB4YIUSebqxwgS7hBDCBP0mR 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=2026-07-13_03,2026-07-10_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 suspectscore=0 spamscore=0 phishscore=0 lowpriorityscore=0 priorityscore=1501 adultscore=0 malwarescore=0 impostorscore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607130153 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/include/asm/kvm_host.h | 1 + arch/s390/kvm/kvm-s390.c | 5 +++++ 2 files changed, 6 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 23c817595e28..374dae6dae81 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -3611,6 +3611,8 @@ 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) @@ -5037,6 +5039,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) kvm_run->kvm_dirty_regs & ~KVM_SYNC_S390_VALID_FIELDS) return -EINVAL; + if (!vcpu->arch.initialized) + return -EINVAL; + vcpu_load(vcpu); if (guestdbg_exit_pending(vcpu)) { -- 2.55.0