From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794591307; b=0v9hsqCadHS1YjroYq684cl90qtA2rIXb7+Qxa3ao2SkGvjmjQ5++NlHGxf+q520L0b3 mMHKCHLHdbGT1VZkOT7ASf0sJMEtR4y+ZgWzEFjuci/tvUz2JA6RU6dKEGWjRBRSnjRPl I61aVZsvlM/wTFzwIT9HId2+37PHFLHIfCyhvsl4OdH38wO6pxm1ydTy7FKrzGM+QDEAQ GNnKKPlEgeacUJBpwnHI66iQbqj7iWnY27WtvuplVPFaUC5Kh6Yg50YYj5VrXgNScObF4 0SapbSuubs0ImnEibM/2g0QFGaUXpSZYwW2wL1BGWwkQxtiDGgsV/XDD2C7qD/IJQAg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794591307; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=gX+3mrv7BfVlIzV41RIg6q+kpu20PCS4urYNluvQg1A=; b=Se7rSemScrmkLgvX0JJUX0cM3EQelIWmKPbrMhhFbl4T2tlaKHZ//gI2d6UcVJL+CofQ QzC2NM41U2JXqWwtOijlFzGffIXJj3nomVeVdRDvSqfDMjMgKWEUf5R1kXbbQHvFzKM6T Li/qCeX6j0gmGEf43SowmVjCBymv4rhVUqAuIjyJnaiAwkxSOVVsgQMhgZv6vutopTw+M QVwBP9d2za/PwbOv81uBO9QeHbh96OCx3sZ7Ss426SkgIncwwVAiBXOZ/jyQ/dfUicM7k y9CyKIyJrT/o4cXhvnekBEIBQiJ0ogzl6oPZGYigRgshGoqt+9knOwxZ3sFhXtmKhNw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b="m7/Z6+Lk"; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 363016077D78; Fri, 13 Nov 2026 17:35:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=m7/Z6+Lk Received: by smtp.kernel.org (Postfix) with ESMTPSA id DD1D61F000C5; Fri, 13 Nov 2026 17:35:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1794591307; bh=gX+3mrv7BfVlIzV41RIg6q+kpu20PCS4urYNluvQg1A=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=m7/Z6+Lk3fm9rMg8ZWJjc4vlBn2WmPnDSl2biX3GvrMZFtTDXN5LhcO2AAbcFMF0j Bs9tSj8BoXDmrsnWNuiv+JbQlo9lqaiJ2P2W5jIxs1r7NE55wdQaZD5IvlpRpv6bSo XX0KUKnretQKepicYY5ryHb1aFlqbrRsJKzcW86Y= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Ge Yang , Muchun Song , Oscar Salvador , Baolin Wang , Barry Song <21cnbao@gmail.com>, David Hildenbrand , Andrew Morton , Mark Bundschuh , Sasha Levin Subject: [PATCH 6.12 420/670] mm/hugetlb: fix kernel NULL pointer dereference when replacing free hugetlb folios Date: Fri, 13 Nov 2026 10:49:44 -0500 Message-ID: <20261113153825.974989621@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261113153811.177190860@linuxfoundation.org> References: <20261113153811.177190860@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: patches@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ge Yang [ Upstream commit 113ed54ad276c352ee5ce109bdcf0df118a43bda ] A kernel crash was observed when replacing free hugetlb folios: BUG: kernel NULL pointer dereference, address: 0000000000000028 PGD 0 P4D 0 Oops: Oops: 0000 [#1] SMP NOPTI CPU: 28 UID: 0 PID: 29639 Comm: test_cma.sh Tainted 6.15.0-rc6-zp #41 PREEMPT(voluntary) RIP: 0010:alloc_and_dissolve_hugetlb_folio+0x1d/0x1f0 RSP: 0018:ffffc9000b30fa90 EFLAGS: 00010286 RAX: 0000000000000000 RBX: 0000000000342cca RCX: ffffea0043000000 RDX: ffffc9000b30fb08 RSI: ffffea0043000000 RDI: 0000000000000000 RBP: ffffc9000b30fb20 R08: 0000000000001000 R09: 0000000000000000 R10: ffff88886f92eb00 R11: 0000000000000000 R12: ffffea0043000000 R13: 0000000000000000 R14: 00000000010c0200 R15: 0000000000000004 FS: 00007fcda5f14740(0000) GS:ffff8888ec1d8000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000028 CR3: 0000000391402000 CR4: 0000000000350ef0 Call Trace: replace_free_hugepage_folios+0xb6/0x100 alloc_contig_range_noprof+0x18a/0x590 ? srso_return_thunk+0x5/0x5f ? down_read+0x12/0xa0 ? srso_return_thunk+0x5/0x5f cma_range_alloc.constprop.0+0x131/0x290 __cma_alloc+0xcf/0x2c0 cma_alloc_write+0x43/0xb0 simple_attr_write_xsigned.constprop.0.isra.0+0xb2/0x110 debugfs_attr_write+0x46/0x70 full_proxy_write+0x62/0xa0 vfs_write+0xf8/0x420 ? srso_return_thunk+0x5/0x5f ? filp_flush+0x86/0xa0 ? srso_return_thunk+0x5/0x5f ? filp_close+0x1f/0x30 ? srso_return_thunk+0x5/0x5f ? do_dup2+0xaf/0x160 ? srso_return_thunk+0x5/0x5f ksys_write+0x65/0xe0 do_syscall_64+0x64/0x170 entry_SYSCALL_64_after_hwframe+0x76/0x7e There is a potential race between __update_and_free_hugetlb_folio() and replace_free_hugepage_folios(): CPU1 CPU2 __update_and_free_hugetlb_folio replace_free_hugepage_folios folio_test_hugetlb(folio) -- It's still hugetlb folio. __folio_clear_hugetlb(folio) hugetlb_free_folio(folio) h = folio_hstate(folio) -- Here, h is NULL pointer When the above race condition occurs, folio_hstate(folio) returns NULL, and subsequent access to this NULL pointer will cause the system to crash. To resolve this issue, execute folio_hstate(folio) under the protection of the hugetlb_lock lock, ensuring that folio_hstate(folio) does not return NULL. Link: https://lkml.kernel.org/r/1747884137-26685-1-git-send-email-yangge1116@126.com Fixes: 04f13d241b8b ("mm: replace free hugepage folios after migration") Signed-off-by: Ge Yang Reviewed-by: Muchun Song Reviewed-by: Oscar Salvador Cc: Baolin Wang Cc: Barry Song <21cnbao@gmail.com> Cc: David Hildenbrand Cc: Signed-off-by: Andrew Morton Signed-off-by: Mark Bundschuh Signed-off-by: Sasha Levin --- mm/hugetlb.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 929ea7dbd9007..0f72edd252250 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -3012,12 +3012,20 @@ int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn) while (start_pfn < end_pfn) { folio = pfn_folio(start_pfn); + + /* + * The folio might have been dissolved from under our feet, so make sure + * to carefully check the state under the lock. + */ + spin_lock_irq(&hugetlb_lock); if (folio_test_hugetlb(folio)) { h = folio_hstate(folio); } else { + spin_unlock_irq(&hugetlb_lock); start_pfn++; continue; } + spin_unlock_irq(&hugetlb_lock); if (!folio_ref_count(folio)) { ret = alloc_and_dissolve_hugetlb_folio(h, folio, -- 2.53.0