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Message-ID: <742701F5-3B2E-45AA-BBEC-69C76E49E3AC@nvidia.com>
Date: Fri, 14 Feb 2025 18:26:25 -0500
From: Zi Yan <ziy@...dia.com>
To: syzbot <syzbot+012c6245eaea0e23f7f9@...kaller.appspotmail.com>
Cc: akpm@...ux-foundation.org, hughd@...gle.com, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [mm?] general protection fault in shmem_mapping
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@...dia.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@...kaller.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
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
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