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Tue, 5 Aug 2025 12:16:21 +0000 (GMT) Date: Tue, 5 Aug 2025 14:16:20 +0200 From: Steffen Eiden To: Claudio Imbrenda Cc: linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, kvm@vger.kernel.org, david@redhat.com, frankja@linux.ibm.com, nsg@linux.ibm.com, nrb@linux.ibm.com, schlameuss@linux.ibm.com, hca@linux.ibm.com, mhartmay@linux.ibm.com, borntraeger@de.ibm.com Subject: Re: [PATCH v1 1/2] KVM: s390: Fix incorrect usage of mmu_notifier_register() Message-ID: <20250805121620.40333-A-seiden@linux.ibm.com> References: <20250805111446.40937-1-imbrenda@linux.ibm.com> <20250805111446.40937-2-imbrenda@linux.ibm.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250805111446.40937-2-imbrenda@linux.ibm.com> X-TM-AS-GCONF: 00 X-Proofpoint-GUID: WMQjuGt9IewnMUVoGm2uYs9iMyWuKIB5 X-Authority-Analysis: v=2.4 cv=M65NKzws c=1 sm=1 tr=0 ts=6891f61a cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=kj9zAlcOel0A:10 a=2OwXVqhp2XgA:10 a=VnNF1IyMAAAA:8 a=K31ow5K9QUr3fs6wkioA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-ORIG-GUID: WMQjuGt9IewnMUVoGm2uYs9iMyWuKIB5 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwODA1MDA4NiBTYWx0ZWRfX98l0a9BTBrvt G6+ZQ+ZA9iKFK+ixC4IN1UycxlhCq3vLHvRvpqFO9HdEoDFTjCbdJBwcNR87dAZ0C02di6hQKcO 5e/wicD6JvW0q/+WzPz9MmbyZhK/TEzTjkIXUh8vDHyFJT+KF1dHJD5jsjDMyrEnFlFHoX7r6O/ E4d9fw10Mh0SAqjhmGpbjwf+CT55tlSEod0G8Cgrzr11j3KCf4Vp1hPv4BVBNPEwcEbD/iYSoum 7B1JLgg1BUc9iWToNVptM/VPuh7EGHlATlj7Xer6Tgh3AyaAK07murJkpaDEdcFN4yK7ZvRmnv8 RW3CScoADwC7hNpl80ud9cjaC+yQcAWiQFosVonuCXNe0Hk1RiYllzEEnewHGM0izJEDu40ozVs fUM/BA7/8hUQNAMlXQlt2O49uBDPbXja1djvmPjhp0XGFsLR6i42acrZ5L1+RzZqSZMsMtL0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-08-05_03,2025-08-04_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 malwarescore=0 spamscore=0 bulkscore=0 lowpriorityscore=0 suspectscore=0 clxscore=1011 mlxscore=0 phishscore=0 priorityscore=1501 mlxlogscore=882 adultscore=0 classifier=spam authscore=0 authtc=n/a authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2505280000 definitions=main-2508050086 On Tue, Aug 05, 2025 at 01:14:45PM +0200, Claudio Imbrenda wrote: > If mmu_notifier_register() fails, for example because a signal was > pending, the mmu_notifier will not be registered. But when the VM gets > destroyed, it will get unregistered anyway and that will cause one > extra mmdrop(), which will eventually cause the mm of the process to > be freed too early, and cause a use-after free. > > This bug happens rarely, and only when secure guests are involved. > > The solution is to check the return value of mmu_notifier_register() > and return it to the caller (ultimately it will be propagated all the > way to userspace). In case of -EINTR, userspace will try again. > > Fixes: ca2fd0609b5d ("KVM: s390: pv: add mmu_notifier") > Signed-off-by: Claudio Imbrenda Reviewed-by: Steffen Eiden