[syzbot] [mm?] kernel BUG in page_table_check_set

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8f5ae30d69d7 Linux 6.17-rc1
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=15f926f0580000
kernel config: https://syzkaller.appspot.com/x/.config?x=8c5ac3d8b8abfcb
dashboard link: https://syzkaller.appspot.com/bug?extid=49a796ed2c9709652f1e
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
userspace arch: arm64
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15faa7a2580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=144143bc580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/18a2e4bd0c4a/disk-8f5ae30d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3b5395881b25/vmlinux-8f5ae30d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e875f4e3b7ff/Image-8f5ae30d.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+49a796...@syzkaller.appspotmail.com

------------[ cut here ]------------
kernel BUG at mm/page_table_check.c:118!
Internal error: Oops - BUG: 00000000f2000800 [#1] SMP
Modules linked in:
CPU: 1 UID: 0 PID: 6740 Comm: syz.0.17 Not tainted 6.17.0-rc1-syzkaller-g8f5ae30d69d7 #0 PREEMPT
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/30/2025
pstate: 83400005 (Nzcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : page_table_check_set+0x584/0x590 mm/page_table_check.c:118
lr : page_table_check_set+0x584/0x590 mm/page_table_check.c:118
sp : ffff80009c9674c0
x29: ffff80009c9674d0 x28: ffff80008fae0000 x27: 0000000000000002
x26: ffff0000c079ca80 x25: 0000000000000001 x24: 0000000000000001
x23: ffff0000c079ca80 x22: 000000000012b950 x21: 0000000000000001
x20: 0000000000000003 x19: 1ffff00012eb65b0 x18: 0000000000000000
x17: 0000000000000000 x16: ffff800080528a28 x15: 0000000000000001
x14: 1fffe000180f3950 x13: 0000000000000000 x12: 0000000000000000
x11: ffff6000180f3951 x10: 0000000000ff0100 x9 : 0000000000000000
x8 : ffff0000cdb05b80 x7 : ffff800080d16554 x6 : 0000000000000000
x5 : 0000000000000000 x4 : 0000000000000000 x3 : ffff800080d15b5c
x2 : 0000000000000001 x1 : 0000000000000002 x0 : 0000000000000001
Call trace:
page_table_check_set+0x584/0x590 mm/page_table_check.c:118 (P)
__page_table_check_ptes_set+0x2a8/0x2e0 mm/page_table_check.c:209
page_table_check_ptes_set include/linux/page_table_check.h:76 [inline]
__set_ptes_anysz arch/arm64/include/asm/pgtable.h:709 [inline]
__set_ptes+0x4a0/0x504 arch/arm64/include/asm/pgtable.h:741
contpte_set_ptes+0x120/0x188 arch/arm64/mm/contpte.c:464
set_ptes arch/arm64/include/asm/pgtable.h:1794 [inline]
modify_prot_commit_ptes+0x4e4/0x694 arch/arm64/mm/mmu.c:1556
prot_commit_flush_ptes mm/mprotect.c:197 [inline]
commit_anon_folio_batch mm/mprotect.c:246 [inline]
set_write_prot_commit_flush_ptes mm/mprotect.c:273 [inline]
change_pte_range mm/mprotect.c:354 [inline]
change_pmd_range mm/mprotect.c:570 [inline]
change_pud_range mm/mprotect.c:633 [inline]
change_p4d_range mm/mprotect.c:659 [inline]
change_protection_range mm/mprotect.c:687 [inline]
change_protection+0x1e84/0x3ff0 mm/mprotect.c:721
mprotect_fixup+0x504/0x744 mm/mprotect.c:837
do_mprotect_pkey+0x864/0xb30 mm/mprotect.c:993
__do_sys_mprotect mm/mprotect.c:1014 [inline]
__se_sys_mprotect mm/mprotect.c:1011 [inline]
__arm64_sys_mprotect+0x80/0x98 mm/mprotect.c:1011
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49
el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132
do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
el0_svc+0x58/0x180 arch/arm64/kernel/entry-common.c:879
el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:898
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596
Code: d4210000 97e865fd d4210000 97e865fb (d4210000)
---[ end trace 0000000000000000 ]---


---
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[Dev Jain]

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git cf1b80dc31a1137b8b4568c138b453bf7453204a

>

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+49a796...@syzkaller.appspotmail.com
Tested-by: syzbot+49a796...@syzkaller.appspotmail.com

Tested on:

commit: cf1b80dc mm: pass page directly instead of using folio..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=116576f0580000
kernel config: https://syzkaller.appspot.com/x/.config?x=dd02560acf543b19

dashboard link: https://syzkaller.appspot.com/bug?extid=49a796ed2c9709652f1e
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
userspace arch: arm64

Note: no patches were applied.
Note: testing is done by a robot and is best-effort only.

[Andrew Morton]

On Thu, 21 Aug 2025 21:16:32 -0700 syzbot <syzbot+49a796...@syzkaller.appspotmail.com> wrote:

> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 8f5ae30d69d7 Linux 6.17-rc1
> git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
> console output: https://syzkaller.appspot.com/x/log.txt?x=15f926f0580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=8c5ac3d8b8abfcb
> dashboard link: https://syzkaller.appspot.com/bug?extid=49a796ed2c9709652f1e
> compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
> userspace arch: arm64
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15faa7a2580000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=144143bc580000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/18a2e4bd0c4a/disk-8f5ae30d.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/3b5395881b25/vmlinux-8f5ae30d.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/e875f4e3b7ff/Image-8f5ae30d.gz.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+49a796...@syzkaller.appspotmail.com
>
> ------------[ cut here ]------------
> kernel BUG at mm/page_table_check.c:118!

Thanks.

Presumably due to the series "Support page table check on PowerPC".
Andrew, could you please take a look?

The series has been in mm.git for a week so I guess the impact of this
is small. I won't drop it at this time, but prompt attention would be
appreciated.

[Pasha Tatashin]

page_table_check_set()
BUG_ON(atomic_inc_return(&ptc->anon_map_count) > 1 && rw);

This code triggers a BUG_ON if we attempt to set a new PTE in a user
page table with RW permission for an anonymous page that is already
mapped elsewhere. Anonymous pages can only be shared with RO
permissions for COW; otherwise, it can't be shared.

Pasha

[Ritesh Harjani]

Andrew Morton <ak...@linux-foundation.org> writes:

> On Thu, 21 Aug 2025 21:16:32 -0700 syzbot <syzbot+49a796...@syzkaller.appspotmail.com> wrote:
>
>> Hello,
>>
>> syzbot found the following issue on:
>>
>> HEAD commit: 8f5ae30d69d7 Linux 6.17-rc1
>> git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
>> console output: https://syzkaller.appspot.com/x/log.txt?x=15f926f0580000
>> kernel config: https://syzkaller.appspot.com/x/.config?x=8c5ac3d8b8abfcb
>> dashboard link: https://syzkaller.appspot.com/bug?extid=49a796ed2c9709652f1e
>> compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
>> userspace arch: arm64
>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15faa7a2580000
>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=144143bc580000
>>
>> Downloadable assets:
>> disk image: https://storage.googleapis.com/syzbot-assets/18a2e4bd0c4a/disk-8f5ae30d.raw.xz
>> vmlinux: https://storage.googleapis.com/syzbot-assets/3b5395881b25/vmlinux-8f5ae30d.xz
>> kernel image: https://storage.googleapis.com/syzbot-assets/e875f4e3b7ff/Image-8f5ae30d.gz.xz
>>
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: syzbot+49a796...@syzkaller.appspotmail.com
>>
>> ------------[ cut here ]------------
>> kernel BUG at mm/page_table_check.c:118!
>
> Thanks.
>
> Presumably due to the series "Support page table check on PowerPC".

The syzbot triggered this on:

HEAD commit: 8f5ae30d69d7 Linux 6.17-rc1
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci

This tree does not have "Support page table check on PowerPC", correct?

Also, I guess Dev's change fixes this reported problem which could happen in
this path: commit_anon_folio_batch() -> change_pte_range() ...

[1]: https://lore.kernel.org/all/2025081206012...@smtp.kernel.org/
[2]: https://lore.kernel.org/all/68a80cc6.050a022...@google.com/

-ritesh

[Andrew Morton]

Yep, sorry.

> Also, I guess Dev's change fixes this reported problem which could happen in
> this path: commit_anon_folio_batch() -> change_pte_range() ...
>
> [1]: https://lore.kernel.org/all/2025081206012...@smtp.kernel.org/
> [2]: https://lore.kernel.org/all/68a80cc6.050a022...@google.com/

Cool. Dev's fix is in 6.17-rc2 as cf1b80dc31a1.

#syz test git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git c17b750b3ad9

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+49a796...@syzkaller.appspotmail.com
Tested-by: syzbot+49a796...@syzkaller.appspotmail.com

Tested on:

commit: c17b750b Linux 6.17-rc2
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=1058a7bc580000
kernel config: https://syzkaller.appspot.com/x/.config?x=34aa432f9050e15d

dashboard link: https://syzkaller.appspot.com/bug?extid=49a796ed2c9709652f1e
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
userspace arch: arm64

[syzbot]

Auto-closing this bug as obsolete.
No recent activity, existing reproducers are no longer triggering the issue.