From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-186.mta1.migadu.com (out-186.mta1.migadu.com [95.215.58.186]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E0BA6240611 for ; Tue, 30 Sep 2025 11:18:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.186 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759231123; cv=none; b=lxXEG6dQeJYjGq7BBJjJKHDGsx86VWdTB5x9ntEwmJWXo1ubTceuR0oU9uWkwbYUiGcrogHXjjbtTHaHtAytmpYhRUW4F/sUxgpGDYBYH/uNsKNixu36FAl+JeV8Tw3Est8lOYgA/JyMZZlfhdT/zFAXwlFCb34dZOikPOClfEM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759231123; c=relaxed/simple; bh=KHYjEziThSNzmIoVCf/6e1q/MRVcwMoJ0+0lY732+2I=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=cCzAU9+B64VzQ8yholYpPiRJ5z7a05j4QSLN/UVJSLCtgmC3lGI41nG+QqE8WdIAcwT65gSL72L4ymvQhtjABPVRE/Nqft9Ow07XBkK5u5zHrj93+MsXxdbvkZzLaORADedi92j/AjjflYH1hFQ81QgwqWd3WdJuyICvkiBTR30= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=r9+wM6V9; arc=none smtp.client-ip=95.215.58.186 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="r9+wM6V9" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1759231107; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=l7QkDw6M9kLZsTy94rmn7kwvsgn47NvjPv3RI5XS+d4=; b=r9+wM6V9DqOKpNvYOmTqpnIt5sLS/pvCN6UDhVikZjU9LEDSt6qoCNQoJxUofnr+miBsaI TMTSEl5uTXVlU94FHq/ui5lrzpmPd1XIC1lPNFbnO7uwezwGNusE3IDWPDO1HiMsA4Gs/U Yo0VtshnNl2k1eA9n5C4cf1wuYwiP08= Date: Tue, 30 Sep 2025 19:17:58 +0800 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [syzbot ci] Re: mm/rmap: fix soft-dirty and uffd-wp bit loss when remapping zero-filled mTHP subpage to shared zeropage Content-Language: en-US To: syzbot ci Cc: syzbot@lists.linux.dev, syzkaller-bugs@googlegroups.com, yuzhao@google.com, ziy@nvidia.com, ying.huang@linux.alibaba.com, jannh@google.com, vbabka@suse.cz, riel@surriel.com, usamaarif642@gmail.com, david@redhat.com, dev.jain@arm.com, akpm@linux-foundation.org, ryan.roberts@arm.com, stable@vger.kernel.org, apopple@nvidia.com, rakie.kim@sk.com, gourry@gourry.net, matthew.brost@intel.com, lorenzo.stoakes@oracle.com, baohua@kernel.org, liam.howlett@oracle.com, ioworker0@gmail.com, harry.yoo@oracle.com, peterx@redhat.com, npache@redhat.com, baolin.wang@linux.alibaba.com, linux-mm@kvack.org, joshua.hahnjy@gmail.com, linux-kernel@vger.kernel.org, byungchul@sk.com References: <68dbb776.a00a0220.102ee.0046.GAE@google.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <68dbb776.a00a0220.102ee.0046.GAE@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT Thanks for the report! On 2025/9/30 18:56, syzbot ci wrote: > syzbot ci has tested the following series > > [v3] mm/rmap: fix soft-dirty and uffd-wp bit loss when remapping zero-filled mTHP subpage to shared zeropage > https://lore.kernel.org/all/20250930060557.85133-1-lance.yang@linux.dev > * [PATCH v3 1/1] mm/rmap: fix soft-dirty and uffd-wp bit loss when remapping zero-filled mTHP subpage to shared zeropage > > and found the following issue: > general protection fault in remove_migration_pte > > Full report is available here: > https://ci.syzbot.org/series/a2021abd-c238-431c-a92e-cc29beb53cbf > > *** > > general protection fault in remove_migration_pte > > tree: torvalds > URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux > base: 1896ce8eb6c61824f6c1125d69d8fda1f44a22f8 > arch: amd64 > compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8 > config: https://ci.syzbot.org/builds/84a2085e-d609-43ea-8b19-f9af8ea3d54a/config > C repro: https://ci.syzbot.org/findings/3e211477-5a8d-4d4d-935b-15076499b001/c_repro > syz repro: https://ci.syzbot.org/findings/3e211477-5a8d-4d4d-935b-15076499b001/syz_repro > > Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN PTI > KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] This is a known issue that I introduced in the v3 patch. I spotted this exact NULL pointer dereference bug[1] myself and have already sent out a v5 version[2] with the fix. The root cause is that ptep_get() is called before the !pwmw.pte check, which handles PMD-mapped THP migration entries. [1] https://lore.kernel.org/linux-mm/2d21c9bc-e299-4ca6-85ba-b01a1f346d9d@linux.dev [2] https://lore.kernel.org/linux-mm/20250930081040.80926-1-lance.yang@linux.dev Thanks, Lance > CPU: 0 UID: 0 PID: 5985 Comm: syz.0.27 Not tainted syzkaller #0 PREEMPT(full) > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 > RIP: 0010:ptep_get include/linux/pgtable.h:340 [inline] > RIP: 0010:remove_migration_pte+0x37f/0x2340 mm/migrate.c:361 > Code: 43 20 48 89 84 24 08 01 00 00 49 8d 47 40 48 89 84 24 00 01 00 00 4c 89 64 24 50 4c 8b b4 24 70 01 00 00 4c 89 f0 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 f7 e8 22 3e ff ff 49 8b 06 48 89 44 24 > RSP: 0018:ffffc90002c2f3c0 EFLAGS: 00010246 > RAX: 0000000000000000 RBX: ffff888027799080 RCX: 1ffffd40008d1006 > RDX: 0000000000000000 RSI: 00000000000387ff RDI: 0000000000038600 > RBP: ffffc90002c2f5d0 R08: 0000000000000003 R09: 0000000000000004 > R10: dffffc0000000000 R11: fffff52000585e30 R12: ffffea0004688008 > R13: dffffc0000000000 R14: 0000000000000000 R15: ffffea0004688000 > FS: 0000555589124500(0000) GS:ffff8880b8d7e000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000200000000300 CR3: 0000000026118000 CR4: 00000000000006f0 > Call Trace: > > rmap_walk_anon+0x553/0x730 mm/rmap.c:2842 > remove_migration_ptes mm/migrate.c:478 [inline] > migrate_folio_move mm/migrate.c:1394 [inline] > migrate_folios_move mm/migrate.c:1725 [inline] > migrate_pages_batch+0x200a/0x35c0 mm/migrate.c:1972 > migrate_pages_sync mm/migrate.c:2002 [inline] > migrate_pages+0x1bcc/0x2930 mm/migrate.c:2111 > migrate_to_node mm/mempolicy.c:1244 [inline] > do_migrate_pages+0x5ee/0x800 mm/mempolicy.c:1343 > kernel_migrate_pages mm/mempolicy.c:1858 [inline] > __do_sys_migrate_pages mm/mempolicy.c:1876 [inline] > __se_sys_migrate_pages+0x544/0x650 mm/mempolicy.c:1872 > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] > do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > RIP: 0033:0x7f922b98ec29 > Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 > RSP: 002b:00007ffccaf966f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000100 > RAX: ffffffffffffffda RBX: 00007f922bbd5fa0 RCX: 00007f922b98ec29 > RDX: 0000200000000300 RSI: 0000000000000003 RDI: 0000000000000000 > RBP: 00007f922ba11e41 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000200000000040 R11: 0000000000000246 R12: 0000000000000000 > R13: 00007f922bbd5fa0 R14: 00007f922bbd5fa0 R15: 0000000000000004 > > Modules linked in: > ---[ end trace 0000000000000000 ]--- > RIP: 0010:ptep_get include/linux/pgtable.h:340 [inline] > RIP: 0010:remove_migration_pte+0x37f/0x2340 mm/migrate.c:361 > Code: 43 20 48 89 84 24 08 01 00 00 49 8d 47 40 48 89 84 24 00 01 00 00 4c 89 64 24 50 4c 8b b4 24 70 01 00 00 4c 89 f0 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 f7 e8 22 3e ff ff 49 8b 06 48 89 44 24 > RSP: 0018:ffffc90002c2f3c0 EFLAGS: 00010246 > RAX: 0000000000000000 RBX: ffff888027799080 RCX: 1ffffd40008d1006 > RDX: 0000000000000000 RSI: 00000000000387ff RDI: 0000000000038600 > RBP: ffffc90002c2f5d0 R08: 0000000000000003 R09: 0000000000000004 > R10: dffffc0000000000 R11: fffff52000585e30 R12: ffffea0004688008 > R13: dffffc0000000000 R14: 0000000000000000 R15: ffffea0004688000 > FS: 0000555589124500(0000) GS:ffff8880b8d7e000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000200000000300 CR3: 0000000026118000 CR4: 00000000000006f0 > ---------------- > Code disassembly (best guess): > 0: 43 20 48 89 rex.XB and %cl,-0x77(%r8) > 4: 84 24 08 test %ah,(%rax,%rcx,1) > 7: 01 00 add %eax,(%rax) > 9: 00 49 8d add %cl,-0x73(%rcx) > c: 47 rex.RXB > d: 40 rex > e: 48 89 84 24 00 01 00 mov %rax,0x100(%rsp) > 15: 00 > 16: 4c 89 64 24 50 mov %r12,0x50(%rsp) > 1b: 4c 8b b4 24 70 01 00 mov 0x170(%rsp),%r14 > 22: 00 > 23: 4c 89 f0 mov %r14,%rax > 26: 48 c1 e8 03 shr $0x3,%rax > * 2a: 42 80 3c 28 00 cmpb $0x0,(%rax,%r13,1) <-- trapping instruction > 2f: 74 08 je 0x39 > 31: 4c 89 f7 mov %r14,%rdi > 34: e8 22 3e ff ff call 0xffff3e5b > 39: 49 8b 06 mov (%r14),%rax > 3c: 48 rex.W > 3d: 89 .byte 0x89 > 3e: 44 rex.R > 3f: 24 .byte 0x24 > > > *** > > If these findings have caused you to resend the series or submit a > separate fix, please add the following tag to your commit message: > Tested-by: syzbot@syzkaller.appspotmail.com > > --- > This report is generated by a bot. It may contain errors. > syzbot ci engineers can be reached at syzkaller@googlegroups.com.