From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-178.mta0.migadu.com (out-178.mta0.migadu.com [91.218.175.178]) (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 547F827B328 for ; Tue, 30 Sep 2025 11:20:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759231242; cv=none; b=tse+zlgRFHYDNCGMazn4NkG7MeI3ujUbNFiayCEWasGntbDXwy2yq8Z1ZRP3YkJqTJuJ0dxy5yB/gOuIK0f+21w622uQt2iOFfPNJ2Ey7T9dSvzj1dXcr0o+netRtD29hGAh3llILWVH8cP1kUD06czCP3Lx3hzmrD6yhKwKAgU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759231242; c=relaxed/simple; bh=4XN0NYoPtAzx19N0avneoLlVcPYM9dOyssM9uDjtj7A=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=UkhFPTSzp3eD7vV56E6kV8mQn8myb1TqxwOE6D6khJIJ5c9362wvT0V+nb9wc0sH0UniWEpPsBA8QjpSFuaWbi6CDK/yEAan8Hx84hf22ZlJd6N/7Y8mfBP8wHYqiAV4+lXCgS07mo1o9YPXLej5kZhbmSFjker2iwB4tthrz50= 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=NwR4r4Y0; arc=none smtp.client-ip=91.218.175.178 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="NwR4r4Y0" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1759231237; 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=FwItMkCXdMaYwI2Rw03q5KkFnMdZIJjcXXc+fJQ+dcM=; b=NwR4r4Y01p8bjyaYC2Cb+KDyNJfvm65DPlrkQwIIuK4GySHW+teXi5V/VZoIQmwBsOF9QJ 195hhGBcC5XcbY0uotAldgCMQ6LUsRE4r23TXSNBmr0fD4APWT38tyPtxjFNFlgSMUo8+E y+U25NBfb7aXWLuuFxytFy9omxROj9s= Date: Tue, 30 Sep 2025 19:20:23 +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, liam.howlett@oracle.com, usamaarif642@gmail.com, rakie.kim@sk.com, david@redhat.com, dev.jain@arm.com, ioworker0@gmail.com, syzkaller-bugs@googlegroups.com, ziy@nvidia.com, byungchul@sk.com, baolin.wang@linux.alibaba.com, akpm@linux-foundation.org, apopple@nvidia.com, vbabka@suse.cz, joshua.hahnjy@gmail.com, gourry@gourry.net, linux-mm@kvack.org, matthew.brost@intel.com, lorenzo.stoakes@oracle.com, ying.huang@linux.alibaba.com, linux-kernel@vger.kernel.org, baohua@kernel.org, npache@redhat.com, yuzhao@google.com, ryan.roberts@arm.com, riel@surriel.com, stable@vger.kernel.org, peterx@redhat.com, jannh@google.com, harry.yoo@oracle.com References: <68dbbc27.a00a0220.102ee.0047.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: <68dbbc27.a00a0220.102ee.0047.GAE@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 2025/9/30 19:16, syzbot ci wrote: > syzbot ci has tested the following series > > [v4] mm/rmap: fix soft-dirty and uffd-wp bit loss when remapping zero-filled mTHP subpage to shared zeropage > https://lore.kernel.org/all/20250930071053.36158-1-lance.yang@linux.dev > * [PATCH v4 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/8cc7e52f-a859-4251-bd08-9787cdaf7928 > > *** > > general protection fault in remove_migration_pte > > tree: linux-next > URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/next/linux-next > base: 262858079afde6d367ce3db183c74d8a43a0e83f > 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/97ee4826-5d29-472d-a85d-51543b0e45de/config > C repro: https://ci.syzbot.org/findings/f4819db2-21f2-4280-8bc4-942445398953/c_repro > syz repro: https://ci.syzbot.org/findings/f4819db2-21f2-4280-8bc4-942445398953/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: 6025 Comm: syz.0.17 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+0x369/0x2320 mm/migrate.c:352 > Code: 00 48 8d 43 20 48 89 44 24 68 49 8d 47 40 48 89 84 24 e8 00 00 00 4c 89 64 24 48 4c 8b b4 24 50 01 00 00 4c 89 f0 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 f7 e8 f8 3e ff ff 49 8b 06 48 89 44 24 > RSP: 0018:ffffc90002fb73e0 EFLAGS: 00010246 > RAX: 0000000000000000 RBX: ffff88802957e300 RCX: 1ffffd40008c9006 > RDX: 0000000000000000 RSI: 0000000000030dff RDI: 0000000000030c00 > RBP: ffffc90002fb75d0 R08: 0000000000000003 R09: 0000000000000004 > R10: dffffc0000000000 R11: fffff520005f6e34 R12: ffffea0004648008 > R13: dffffc0000000000 R14: 0000000000000000 R15: ffffea0004648000 > FS: 00005555624de500(0000) GS:ffff8880b83fc000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000200000000300 CR3: 000000010d8b8000 CR4: 00000000000006f0 > Call Trace: > > rmap_walk_anon+0x553/0x730 mm/rmap.c:2855 > remove_migration_ptes mm/migrate.c:469 [inline] > migrate_folio_move mm/migrate.c:1381 [inline] > migrate_folios_move mm/migrate.c:1711 [inline] > migrate_pages_batch+0x202e/0x35e0 mm/migrate.c:1967 > migrate_pages_sync mm/migrate.c:1997 [inline] > migrate_pages+0x1bcc/0x2930 mm/migrate.c:2106 > 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/0xfa0 arch/x86/entry/syscall_64.c:94 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > RIP: 0033:0x7fb18e18ec29 > 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:00007ffdca5c9838 EFLAGS: 00000246 ORIG_RAX: 0000000000000100 > RAX: ffffffffffffffda RBX: 00007fb18e3d5fa0 RCX: 00007fb18e18ec29 > RDX: 0000200000000300 RSI: 0000000000000003 RDI: 0000000000000000 > RBP: 00007fb18e211e41 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000200000000040 R11: 0000000000000246 R12: 0000000000000000 > R13: 00007fb18e3d5fa0 R14: 00007fb18e3d5fa0 R15: 0000000000000004 > > Modules linked in: > ---[ end trace 0000000000000000 ]--- > RIP: 0010:ptep_get include/linux/pgtable.h:340 [inline] > RIP: 0010:remove_migration_pte+0x369/0x2320 mm/migrate.c:352 > Code: 00 48 8d 43 20 48 89 44 24 68 49 8d 47 40 48 89 84 24 e8 00 00 00 4c 89 64 24 48 4c 8b b4 24 50 01 00 00 4c 89 f0 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 f7 e8 f8 3e ff ff 49 8b 06 48 89 44 24 > RSP: 0018:ffffc90002fb73e0 EFLAGS: 00010246 > RAX: 0000000000000000 RBX: ffff88802957e300 RCX: 1ffffd40008c9006 > RDX: 0000000000000000 RSI: 0000000000030dff RDI: 0000000000030c00 > RBP: ffffc90002fb75d0 R08: 0000000000000003 R09: 0000000000000004 > R10: dffffc0000000000 R11: fffff520005f6e34 R12: ffffea0004648008 > R13: dffffc0000000000 R14: 0000000000000000 R15: ffffea0004648000 > FS: 00005555624de500(0000) GS:ffff8880b83fc000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000200000000300 CR3: 000000010d8b8000 CR4: 00000000000006f0 > ---------------- > Code disassembly (best guess): > 0: 00 48 8d add %cl,-0x73(%rax) > 3: 43 20 48 89 rex.XB and %cl,-0x77(%r8) > 7: 44 24 68 rex.R and $0x68,%al > a: 49 8d 47 40 lea 0x40(%r15),%rax > e: 48 89 84 24 e8 00 00 mov %rax,0xe8(%rsp) > 15: 00 > 16: 4c 89 64 24 48 mov %r12,0x48(%rsp) > 1b: 4c 8b b4 24 50 01 00 mov 0x150(%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 f8 3e ff ff call 0xffff3f31 > 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.