[syzbot] [mm?] general protection fault in shmem_mapping

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: df5d6180169a Add linux-next specific files for 20250210
git tree: linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=16d343f8580000
kernel config: https://syzkaller.appspot.com/x/.config?x=2cd616b6e736ca7
dashboard link: https://syzkaller.appspot.com/bug?extid=012c6245eaea0e23f7f9
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=138972a4580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11737b18580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/92495cf20271/disk-df5d6180.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/4b3656161842/vmlinux-df5d6180.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7fbc4e7a0f5d/bzImage-df5d6180.xz

The issue was bisected to:

commit 19c067c8a0f18b62d4a4235b0b327624c86f2e40
Author: Zi Yan <z...@nvidia.com>
Date: Wed Feb 5 03:14:13 2025 +0000

mm/huge_memory: add buddy allocator like folio_split()

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=102f9bdf980000
final oops: https://syzkaller.appspot.com/x/report.txt?x=122f9bdf980000
console output: https://syzkaller.appspot.com/x/log.txt?x=142f9bdf980000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+012c62...@syzkaller.appspotmail.com
Fixes: 19c067c8a0f1 ("mm/huge_memory: add buddy allocator like folio_split()")

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000024: 0000 [#1] PREEMPT SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000120-0x0000000000000127]
CPU: 1 UID: 0 PID: 5949 Comm: syz-executor163 Not tainted 6.14.0-rc2-next-20250210-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
RIP: 0010:shmem_mapping+0x25/0x50 mm/shmem.c:281
Code: 90 90 90 90 90 f3 0f 1e fa 53 48 89 fb e8 c3 3a bd ff 48 81 c3 20 01 00 00 48 89 d8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df <80> 3c 08 00 74 08 48 89 df e8 dd 35 24 00 48 c7 c0 80 6c 14 8c 48
RSP: 0018:ffffc90004036dd8 EFLAGS: 00010006
RAX: 0000000000000024 RBX: 0000000000000120 RCX: dffffc0000000000
RDX: 0000000000000000 RSI: 0000000000000600 RDI: 0000000000000000
RBP: 0000000000000600 R08: ffffffff822bcf18 R09: 1ffffd4000331008
R10: dffffc0000000000 R11: fffff94000331009 R12: ffffea0001988018
R13: ffffea0001988080 R14: ffffea0001988018 R15: ffffea0001988000
FS: 00007f5e045316c0(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f5e0458dae0 CR3: 0000000023c78000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
__split_unmapped_folio+0x238a/0x3e50 mm/huge_memory.c:3587
__folio_split+0x1267/0x16d0 mm/huge_memory.c:3871
try_folio_split include/linux/huge_mm.h:374 [inline]
truncate_inode_partial_folio+0x55d/0xdc0 mm/truncate.c:230
shmem_undo_range+0xab7/0x1820 mm/shmem.c:1144
shmem_truncate_range mm/shmem.c:1224 [inline]
shmem_fallocate+0x431/0xf20 mm/shmem.c:3674
vfs_fallocate+0x623/0x7a0 fs/open.c:338
madvise_remove mm/madvise.c:1034 [inline]
madvise_vma_behavior mm/madvise.c:1269 [inline]
madvise_walk_vmas mm/madvise.c:1511 [inline]
madvise_do_behavior+0x1f29/0x3c00 mm/madvise.c:1646
do_madvise mm/madvise.c:1744 [inline]
__do_sys_madvise mm/madvise.c:1752 [inline]
__se_sys_madvise mm/madvise.c:1750 [inline]
__x64_sys_madvise+0x11b/0x140 mm/madvise.c:1750
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5e04576519
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 18 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f5e04531218 EFLAGS: 00000246 ORIG_RAX: 000000000000001c
RAX: ffffffffffffffda RBX: 00007f5e04600308 RCX: 00007f5e04576519
RDX: 0000000000000009 RSI: 0000000000600003 RDI: 0000400000000000
RBP: 00007f5e04600300 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f5e045cd074
R13: 0000400000000000 R14: 0000400000000140 R15: 0000400000000040
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:shmem_mapping+0x25/0x50 mm/shmem.c:281
Code: 90 90 90 90 90 f3 0f 1e fa 53 48 89 fb e8 c3 3a bd ff 48 81 c3 20 01 00 00 48 89 d8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df <80> 3c 08 00 74 08 48 89 df e8 dd 35 24 00 48 c7 c0 80 6c 14 8c 48
RSP: 0018:ffffc90004036dd8 EFLAGS: 00010006
RAX: 0000000000000024 RBX: 0000000000000120 RCX: dffffc0000000000
RDX: 0000000000000000 RSI: 0000000000000600 RDI: 0000000000000000
RBP: 0000000000000600 R08: ffffffff822bcf18 R09: 1ffffd4000331008
R10: dffffc0000000000 R11: fffff94000331009 R12: ffffea0001988018
R13: ffffea0001988080 R14: ffffea0001988018 R15: ffffea0001988000
FS: 00007f5e045316c0(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f5e0458dae0 CR3: 0000000023c78000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
0: 90 nop
1: 90 nop
2: 90 nop
3: 90 nop
4: 90 nop
5: f3 0f 1e fa endbr64
9: 53 push %rbx
a: 48 89 fb mov %rdi,%rbx
d: e8 c3 3a bd ff call 0xffbd3ad5
12: 48 81 c3 20 01 00 00 add $0x120,%rbx
19: 48 89 d8 mov %rbx,%rax
1c: 48 c1 e8 03 shr $0x3,%rax
20: 48 b9 00 00 00 00 00 movabs $0xdffffc0000000000,%rcx
27: fc ff df
* 2a: 80 3c 08 00 cmpb $0x0,(%rax,%rcx,1) <-- trapping instruction
2e: 74 08 je 0x38
30: 48 89 df mov %rbx,%rdi
33: e8 dd 35 24 00 call 0x243615
38: 48 c7 c0 80 6c 14 8c mov $0xffffffff8c146c80,%rax
3f: 48 rex.W


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[Zi Yan]

On 14 Feb 2025, at 10:48, syzbot wrote:

> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: df5d6180169a Add linux-next specific files for 20250210
> git tree: linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=16d343f8580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=2cd616b6e736ca7
> dashboard link: https://syzkaller.appspot.com/bug?extid=012c6245eaea0e23f7f9
> compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=138972a4580000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11737b18580000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/92495cf20271/disk-df5d6180.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/4b3656161842/vmlinux-df5d6180.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/7fbc4e7a0f5d/bzImage-df5d6180.xz
>
> The issue was bisected to:
>
> commit 19c067c8a0f18b62d4a4235b0b327624c86f2e40
> Author: Zi Yan <z...@nvidia.com>
> Date: Wed Feb 5 03:14:13 2025 +0000
>
> mm/huge_memory: add buddy allocator like folio_split()
>
> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=102f9bdf980000
> final oops: https://syzkaller.appspot.com/x/report.txt?x=122f9bdf980000
> console output: https://syzkaller.appspot.com/x/log.txt?x=142f9bdf980000

I have reproduced it locally and am working on a fix. Thanks for the reporting.


Best Regards,
Yan, Zi

[Zi Yan]

On 14 Feb 2025, at 10:48, syzbot wrote:

#syz test: github.com:x-y-z/linux-1gb-thp.git syzkaller_fix_20250114

origin_folio->mapping becomes NULL, since it was dropped, and the remaining
after-split folios are still trying to use origin_folio->mapping. It leads
to the error. And the original __split_huge_page() did not check
origin_folio->index nor dropped it. __split_unmapped_folio() should keep
the original behavior.

Fixed it by not dropping origin_folio.

My local test do not fail and I am triggering syzbot to test the change
to confirm it.

Best Regards,
Yan, Zi

[syzbot]

"github.com:x-y-z/linux-1gb-thp.git" does not look like a valid git repo address.

[Zi Yan]

#syz test: g...@github.com:x-y-z/linux-1gb-thp.git syzkaller_fix_20250114

Best Regards,
Yan, Zi

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

failed to checkout kernel repo g...@github.com:x-y-z/linux-1gb-thp.git/syzkaller_fix_20250114: failed to run ["git" "fetch" "--force" "21c4e043f63ee530c32221be8efae42773de1c65" "syzkaller_fix_20250114"]: exit status 128
Host key verification failed.
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.



Tested on:

commit: [unknown
git tree: g...@github.com:x-y-z/linux-1gb-thp.git syzkaller_fix_20250114

kernel config: https://syzkaller.appspot.com/x/.config?x=2cd616b6e736ca7
dashboard link: https://syzkaller.appspot.com/bug?extid=012c6245eaea0e23f7f9
compiler:

Note: no patches were applied.

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-...@vger.kernel.org, syzkall...@googlegroups.com.

***

Subject: Re: [syzbot] [mm?] general protection fault in shmem_mapping
Author: z...@nvidia.com

On 14 Feb 2025, at 10:48, syzbot wrote:

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git df5d6180169a



Best Regards,
Yan, Zi

[syzbot]

Hello,

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

Reported-by: syzbot+012c62...@syzkaller.appspotmail.com
Tested-by: syzbot+012c62...@syzkaller.appspotmail.com

Tested on:

commit: df5d6180 Add linux-next specific files for 20250210
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
console output: https://syzkaller.appspot.com/x/log.txt?x=1326d9b0580000

kernel config: https://syzkaller.appspot.com/x/.config?x=2cd616b6e736ca7
dashboard link: https://syzkaller.appspot.com/bug?extid=012c6245eaea0e23f7f9
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

patch: https://syzkaller.appspot.com/x/patch.diff?x=157467df980000

Note: testing is done by a robot and is best-effort only.

[Zi Yan]

On 14 Feb 2025, at 10:48, syzbot wrote:

OK, I figured out how to trigger syzkaller to do the test. The attached
patch includes both the fix and the __split_folio_to_order() change
discussed at https://lore.kernel.org/linux-mm/d989ef66-4a4b-4679...@redhat.com/. I will paste the patch to my original patch
email once syzkaller confirms it fixes the issue.

[syzbot]

Hello,

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

Reported-by: syzbot+012c62...@syzkaller.appspotmail.com
Tested-by: syzbot+012c62...@syzkaller.appspotmail.com

Tested on:

commit: df5d6180 Add linux-next specific files for 20250210
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git

console output: https://syzkaller.appspot.com/x/log.txt?x=13bd19a4580000

kernel config: https://syzkaller.appspot.com/x/.config?x=2cd616b6e736ca7
dashboard link: https://syzkaller.appspot.com/bug?extid=012c6245eaea0e23f7f9
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

patch: https://syzkaller.appspot.com/x/patch.diff?x=11a7a098580000