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Fri, 14 Aug 2026 16:33:56 +0000 (GMT) Received: from p-imbrenda.ehn-de.ibm.com (unknown [9.224.75.30]) by smtpav03.fra02v.mail.ibm.com (Postfix) with ESMTP; Fri, 14 Aug 2026 16:33:56 +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 6/6] KVM: s390: Fix potential races in dat skey functions Date: Fri, 14 Aug 2026 18:33:55 +0200 Message-ID: <20260814163355.227191-7-imbrenda@linux.ibm.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260814163355.227191-1-imbrenda@linux.ibm.com> References: <20260814163355.227191-1-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: AW1haW4tMjYwODE0MDEyNiBTYWx0ZWRfXxL92De1rqMGZ 7sdGALrJNKETCECN5G5OWwJAygdcdzyIHGUwkgclti7KKkxEoJOgUEuKRXYT486/c+DpjK0mZqw uzUuLToPWITXGn3403MoPac7bc58+PrSPbxL4N5iP85U3bO90uzJO297kEbP8MNHbK/lJVxJ8U3 roeBWmcrtv3KxyJ65ItsAp13R/OJFYEAkCgFgbp3ZsZOg7rZ1MaVBnrM822g1wGphIgHsxsNdN1 jCJSgPZrYd8LJeeDX7NVr/vchy+CHsuNSqNTDeGlPj7g5yzwDwqqKdr59VBMrXy8KmV3KsPmtWW ck+MPYJu4G7vodeq+mGHVN1fQicHBMYSEV3rYBDmbPCU9OfamWXWH+ZXWznNRtHmQ1X7whlGkqB 2Q3j2wGIwRSlAPIRte1ThwNhkVoFkd+M8CrgRf5xKL9cxE9D1TU/7k+0Xfjbe1frR+xin62MW+P 22qyZeRPvfq51UpWUbA== X-Proofpoint-ORIG-GUID: bTuf-HnmT8aM9nkiVVl4MnnuQHSfopEc X-Proofpoint-Spam-Info: AW1haW4tMjYwODE0MDEyNiBTYWx0ZWRfX8HlPFrKz3HhC u9vh8EEQb88bBGO+vQC0yi2dA93RDPYUkemrJP/F41BS5aldgY7qt716R/AbhIrd3cxAX/w4FIv zBz8VIDB/jEz/dKJuHHPrP1gBYyDhUA= X-Authority-Analysis: v=2.4 cv=IfK3n2qa c=1 sm=1 tr=0 ts=6a7f437b cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VnNF1IyMAAAA:8 a=wCyL4Wiu_ChfG3is39wA:9 X-Proofpoint-GUID: bTuf-HnmT8aM9nkiVVl4MnnuQHSfopEc 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-2608140126 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. Similar issues were also present in dat_set_storage_key(). dat_get_storage_key() and dat_reset_reference_bit() did instead check for a potential concurrent splitting of the large page, but then handled it incorrectly. 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 | 36 ++++++++++++++++++++++++++++-------- 1 file changed, 28 insertions(+), 8 deletions(-) diff --git a/arch/s390/kvm/dat.c b/arch/s390/kvm/dat.c index 7e5dd5a1eb1e..b4c318ebd91e 100644 --- a/arch/s390/kvm/dat.c +++ b/arch/s390/kvm/dat.c @@ -620,17 +620,20 @@ int dat_get_storage_key(union asce asce, gfn_t gfn, union skey *skey) union pte *ptep; int rc; +again: skey->skey = 0; rc = dat_entry_walk(NULL, gfn, asce, DAT_WALK_ANY, TABLE_TYPE_PAGE_TABLE, &crstep, &ptep); if (rc) return rc; if (!ptep) { - union crste crste; + union crste crste = READ_ONCE(*crstep); - crste = READ_ONCE(*crstep); - if (!crste.h.fc || !crste.s.fc1.pr) + if (!crste_leaf(crste)) + goto again; + if (!crste.s.fc1.pr) return 0; + skey->skey = page_get_storage_key(large_crste_to_phys(crste, gfn)); return 0; } @@ -661,13 +664,20 @@ int dat_set_storage_key(struct kvm_s390_mmu_cache *mc, union asce asce, gfn_t gf union pte *ptep; int rc; +again: rc = dat_entry_walk(mc, gfn, asce, DAT_WALK_LEAF_ALLOC, TABLE_TYPE_PAGE_TABLE, &crstep, &ptep); if (rc) return rc; if (!ptep) { - page_set_storage_key(large_crste_to_phys(*crstep, gfn), skey.skey, !nq); + union crste crste = READ_ONCE(*crstep); + + /* A large page has been split concurrently, try again */ + if (!crste_leaf(crste)) + goto again; + + page_set_storage_key(large_crste_to_phys(crste, gfn), skey.skey, !nq); return 0; } @@ -717,15 +727,22 @@ int dat_cond_set_storage_key(struct kvm_s390_mmu_cache *mmc, union asce asce, gf 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) return rc; if (!ptep) { + union crste crste = READ_ONCE(*crstep); + + /* A large page has been split concurrently, try again */ + if (!crste_leaf(crste)) + goto again; if (!oldkey) oldkey = &prev; - return page_cond_set_storage_key(large_crste_to_phys(*crstep, gfn), skey, oldkey, + + return page_cond_set_storage_key(large_crste_to_phys(crste, gfn), skey, oldkey, nq, mr, mc); } @@ -767,7 +784,7 @@ int dat_reset_reference_bit(union asce asce, gfn_t gfn, union skey *skey) int rc; skey->skey = 0; - +again: rc = dat_entry_walk(NULL, gfn, asce, DAT_WALK_ANY, TABLE_TYPE_PAGE_TABLE, &crstep, &ptep); if (rc) return rc; @@ -775,9 +792,12 @@ int dat_reset_reference_bit(union asce asce, gfn_t gfn, union skey *skey) if (!ptep) { union crste crste = READ_ONCE(*crstep); - if (!crste.h.fc || !crste.s.fc1.pr) + /* A large page has been split concurrently, try again */ + if (!crste_leaf(crste)) + goto again; + if (!crste.s.fc1.pr) return 0; - skey->skey = page_reset_referenced(large_crste_to_phys(*crstep, gfn)) << 1; + skey->skey = page_reset_referenced(large_crste_to_phys(crste, gfn)) << 1; return 0; } old = pgste_get_lock(ptep); -- 2.55.0