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Fri, 14 Aug 2026 14:40:43 +0000 (GMT) Received: from p-imbrenda.ehn-de.ibm.com (unknown [9.224.75.30]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Fri, 14 Aug 2026 14:40:43 +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 6/6] KVM: s390: Fix potential race in dat_cond_set_storage_key() Date: Fri, 14 Aug 2026 16:40:41 +0200 Message-ID: <20260814144041.169025-7-imbrenda@linux.ibm.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260814144041.169025-1-imbrenda@linux.ibm.com> References: <20260814144041.169025-1-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-Details-Enc: AW1haW4tMjYwODE0MDExMSBTYWx0ZWRfX0dwewHVWXo6O mUnfrSzOOnUdt2Ho+x4EzcTN8w3ajKrDafrVT0NC3dRJZJgRizayhS9u4Fpf9FXt/8tFGeJxE41 fDykx+Ec/wk11aRZ3ALR3GPHZSs7YkJNEmHpdC1C+zCor7qyI9ABwVVNxmZyREyHdvlwrF2LoP+ tVAZ0dEqn7ETbLH+pEzlLsLPsy4vrhvdp4kBVJT7erbK+gH/Zs3AZ4EVMdGNMJWAGxm4/xbkOzZ mUxINNXFfzhXMR0V9DMBZI220L5dX1JyJlKYkWv+ge7EGWC1hc2y7IxZsgejzcPWxPjo7TN8fLE pWIArowIJgMo/ar/8e5/UTA8hfs4qn94jg92wXAsp+6p09BbMZ7WTg5AFici4mH+0Sy7/OG0ZFi tCf6xidPi5SpqcgS7u4LBYBakOdZsqG6r0/OLodMcy/VxFsnkc4aDYBbPAzrCoHT/Zh9l8lL/nn f4i0b5wMcN/jNyCBshQ== X-Proofpoint-ORIG-GUID: j6L-Yk1GktosYrdKTAhUJ3dSxUZBwv2N X-Proofpoint-Spam-Info: AW1haW4tMjYwODE0MDExMSBTYWx0ZWRfX0h3KUbyeBdpO QeY5eT7SxYXpUHey9yEF1MooNyW0Sn8omkAfcmoKru2pobbGM8fr7DKhjCOCtBwQ8LI+oXZaGgA Z8X2CVzOQ6WiDGGesqsvpjkWUpVGbJ4= X-Authority-Analysis: v=2.4 cv=IfK3n2qa c=1 sm=1 tr=0 ts=6a7f28f2 cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VnNF1IyMAAAA:8 a=wsP9SkaD_1DqgBQrQ4IA:9 X-Proofpoint-GUID: j6L-Yk1GktosYrdKTAhUJ3dSxUZBwv2N X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-14_05,2026-08-12_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 priorityscore=1501 impostorscore=0 bulkscore=0 clxscore=1015 lowpriorityscore=0 adultscore=0 malwarescore=0 spamscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608140111 When dat_cond_set_storage_key() finds a large page, it will conditionally set the storage key in absolute memory using large_crste_to_phys() to get the absolute address. There is a race window between dat_entry_walk() and large_crste_to_phys(): the large page could have been split concurrently, and large_crste_to_phys() might be called with a crste that does not designate a large page, leading to crashes. Fix by performing a READ_ONCE on the crste pointer, checking and using the result, instead of dereferencing the pointer again. In case a race is detacted, try dat_entry_walk() again. Fixes: 8e03e8316eb2 ("KVM: s390: KVM page table management functions: storage keys") Signed-off-by: Claudio Imbrenda --- arch/s390/kvm/dat.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/arch/s390/kvm/dat.c b/arch/s390/kvm/dat.c index 7e5dd5a1eb1e..b467b95689b2 100644 --- a/arch/s390/kvm/dat.c +++ b/arch/s390/kvm/dat.c @@ -713,10 +713,12 @@ int dat_cond_set_storage_key(struct kvm_s390_mmu_cache *mmc, union asce asce, gf { union pgste pgste, old; union crste *crstep; + union crste crste; union skey prev; union pte *ptep; int rc; +again: rc = dat_entry_walk(mmc, gfn, asce, DAT_WALK_LEAF_ALLOC, TABLE_TYPE_PAGE_TABLE, &crstep, &ptep); if (rc) @@ -725,7 +727,11 @@ int dat_cond_set_storage_key(struct kvm_s390_mmu_cache *mmc, union asce asce, gf if (!ptep) { if (!oldkey) oldkey = &prev; - return page_cond_set_storage_key(large_crste_to_phys(*crstep, gfn), skey, oldkey, + crste = READ_ONCE(*crstep); + /* A large page has been split concurrently, try again */ + if (!crste_leaf(crste)) + goto again; + return page_cond_set_storage_key(large_crste_to_phys(crste, gfn), skey, oldkey, nq, mr, mc); } -- 2.55.0