* [syzbot ci] Re: mm/rmap: fix soft-dirty and uffd-wp bit loss when remapping zero-filled mTHP subpage to shared zeropage
[not found] <20250930060557.85133-1-lance.yang@linux.dev>
@ 2025-09-30 10:56 ` syzbot ci
2025-09-30 11:17 ` Lance Yang
0 siblings, 1 reply; 4+ messages in thread
From: syzbot ci @ 2025-09-30 10:56 UTC (permalink / raw)
To: akpm, apopple, baohua, baolin.wang, byungchul, david, dev.jain,
gourry, harry.yoo, ioworker0, jannh, joshua.hahnjy, lance.yang,
liam.howlett, linux-kernel, linux-mm, lorenzo.stoakes,
matthew.brost, npache, peterx, rakie.kim, riel, ryan.roberts,
stable, usamaarif642, vbabka, ying.huang, yuzhao, ziy
Cc: syzbot, syzkaller-bugs
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]
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:
<TASK>
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
</TASK>
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.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [syzbot ci] Re: mm/rmap: fix soft-dirty and uffd-wp bit loss when remapping zero-filled mTHP subpage to shared zeropage
[not found] <20250930071053.36158-1-lance.yang@linux.dev>
@ 2025-09-30 11:16 ` syzbot ci
2025-09-30 11:20 ` Lance Yang
0 siblings, 1 reply; 4+ messages in thread
From: syzbot ci @ 2025-09-30 11:16 UTC (permalink / raw)
To: akpm, apopple, baohua, baolin.wang, byungchul, david, dev.jain,
gourry, harry.yoo, ioworker0, jannh, joshua.hahnjy, lance.yang,
liam.howlett, linux-kernel, linux-mm, lorenzo.stoakes,
matthew.brost, npache, peterx, rakie.kim, riel, ryan.roberts,
stable, usamaarif642, vbabka, ying.huang, yuzhao, ziy
Cc: syzbot, syzkaller-bugs
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]
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:
<TASK>
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
</TASK>
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.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [syzbot ci] Re: mm/rmap: fix soft-dirty and uffd-wp bit loss when remapping zero-filled mTHP subpage to shared zeropage
2025-09-30 10:56 ` [syzbot ci] Re: mm/rmap: fix soft-dirty and uffd-wp bit loss when remapping zero-filled mTHP subpage to shared zeropage syzbot ci
@ 2025-09-30 11:17 ` Lance Yang
0 siblings, 0 replies; 4+ messages in thread
From: Lance Yang @ 2025-09-30 11:17 UTC (permalink / raw)
To: syzbot ci
Cc: syzbot, syzkaller-bugs, yuzhao, ziy, ying.huang, jannh, vbabka,
riel, usamaarif642, david, dev.jain, akpm, ryan.roberts, stable,
apopple, rakie.kim, gourry, matthew.brost, lorenzo.stoakes,
baohua, liam.howlett, ioworker0, harry.yoo, peterx, npache,
baolin.wang, linux-mm, joshua.hahnjy, linux-kernel, byungchul
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:
> <TASK>
> 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
> </TASK>
> 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.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [syzbot ci] Re: mm/rmap: fix soft-dirty and uffd-wp bit loss when remapping zero-filled mTHP subpage to shared zeropage
2025-09-30 11:16 ` syzbot ci
@ 2025-09-30 11:20 ` Lance Yang
0 siblings, 0 replies; 4+ messages in thread
From: Lance Yang @ 2025-09-30 11:20 UTC (permalink / raw)
To: syzbot ci
Cc: syzbot, liam.howlett, usamaarif642, rakie.kim, david, dev.jain,
ioworker0, syzkaller-bugs, ziy, byungchul, baolin.wang, akpm,
apopple, vbabka, joshua.hahnjy, gourry, linux-mm, matthew.brost,
lorenzo.stoakes, ying.huang, linux-kernel, baohua, npache, yuzhao,
ryan.roberts, riel, stable, peterx, jannh, harry.yoo
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:
> <TASK>
> 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
> </TASK>
> 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.
^ permalink raw reply [flat|nested] 4+ messages in thread
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2025-09-30 10:56 ` [syzbot ci] Re: mm/rmap: fix soft-dirty and uffd-wp bit loss when remapping zero-filled mTHP subpage to shared zeropage syzbot ci
2025-09-30 11:17 ` Lance Yang
[not found] <20250930071053.36158-1-lance.yang@linux.dev>
2025-09-30 11:16 ` syzbot ci
2025-09-30 11:20 ` Lance Yang
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