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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 X-Rspamd-Queue-Id: 5F9401C000A X-Stat-Signature: 7jp1qudd7ghd7mh5td833woab45bm8xb X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1759231240-628448 X-HE-Meta: U2FsdGVkX1+9tOY3G/juTbC2Wp/ZPgDCM/n2zWRGJ9PpPQ9i7jjhbL2+BRBDsehzSkwHuJV35x0rmPiC2jq3STBjj8QbdbEOfgI31M9/4xp0jQ9wTYiOG3/t78s8u5L3G2TubvF4zRW+SaDz84F/sGgKAUfbL2LvgmZkFiZDdkVu7gHnlcD8g894WqFsWBKC7y9r3obUgf8z4mPaM/V1Ba2azGdkqJy3dCZrQPwks8+KEgawn7PHI6Ilm6mycCbFzGkOSvQxMZXf2T7TA7Mm/bXQ2H9Ib4bnDox3vZJKve/IUR0ixKFGtBzPqEj/IknIxQn6A9u6Jtj/01L29Lqf8H2PY+pdWTfi+/5khKSUsllKIEi+U1d8lLFqVM94Mf4ImMGx/ZF/XCiDq/NAbbUGbqD567T5ie4vbnzEHT6OdMwShs+ZAn7bS1vDgJ3WBUS3EG1e2HxzmC6BSi7IBv5KOML3b26LKbpF02WckZnr9C19J1U7OdWbk2eYhR5Jd5qzIxJKx1fLU20nDFPM1wn59wC0e5dyat6EYPMLfntZjexS86B43SeK7Y2p0keptQEH6bsWtqjzUnnYd6TuxABE/BL6xJ5OrtjclMQmd99SEA+ZiYg7QFtkQfqo9ND0lO7tTL8S57VcpiUaxkWZIcfRZQWuh+TM7Pg5fTdIkc94IaFBncJ/RQOFSHM/1jfOVtrq8e7T8rR0Dp2QnEfb1dqBPtn8HPXoQ51dfOl+Rg13pqdAcjFxAARcKcnTPKeTENd7ypzHOJbMiqx3tJV+pu2j9JMlaAs+0LDSh3uj84y7QXYCQTSMV25jrah/SaN2sXmxw0Gnc6ryc4DrgTCsxngA0h9EUg+wjkdMUvG3FX+cMMJE+azIIfzEpxFuV6vv4OE1q8fTQMkl/7UJMXqDVy8VqMk5HoAsbjaethrVwhVyu3k6/52jJrgeYzysVrH7EL7hZxynlwiXUQCgyfqmy+c Mo0Z1syC 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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.