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

[syzbot <syzbot+012c6245eaea0e23f7f9@syzkaller.appspotmail.com>]

> 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 <ziy@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+012c6245eaea0e23f7f9@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
>>
>
>
> #syz test: github.com:x-y-z/linux-1gb-thp.git syzkaller_fix_20250114

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

>
> 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