Re: [syzbot] [bpf?] [net?] BUG: unable to handle kernel paging request in bpf_prog_ADDR (3)

[Yonghong Song]

On 7/13/24 9:24 AM, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    8b9b59e27aa8 i40e: fix: remove needless retries of NVM upd..
> git tree:       bpf
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=135ee4f6980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=b63b35269462a0e0
> dashboard link: https://syzkaller.appspot.com/bug?extid=ad9ec60c8eaf69e6f99c
> 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=171399dd980000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10e4054e980000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/535b0bcd3e1f/disk-8b9b59e2.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/127f5ddff150/vmlinux-8b9b59e2.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/a3ac9910529c/bzImage-8b9b59e2.xz
>
> The issue was bisected to:
>
> commit 1f1e864b65554e33fe74e3377e58b12f4302f2eb
> Author: Yonghong Song <yonghong.song@xxxxxxxxx>
> Date:   Fri Jul 28 01:12:07 2023 +0000
>
>      bpf: Handle sign-extenstin ctx member accesses
>
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=121c054e980000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=111c054e980000
> console output: https://syzkaller.appspot.com/x/log.txt?x=161c054e980000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+ad9ec60c8eaf69e6f99c@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 1f1e864b6555 ("bpf: Handle sign-extenstin ctx member accesses")
>
> BUG: unable to handle page fault for address: 000000002aebd040
> #PF: supervisor read access in kernel mode
> #PF: error_code(0x0000) - not-present page
> PGD 80000000226b6067 P4D 80000000226b6067 PUD 226b7067 PMD 0
> Oops: Oops: 0000 [#1] PREEMPT SMP KASAN PTI
> CPU: 0 PID: 5096 Comm: syz-executor365 Not tainted 6.10.0-rc7-syzkaller-00133-g8b9b59e27aa8 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
> RIP: 0010:bpf_prog_82ec301e76077160+0x5c/0xa0
> Code: 0a b8 02 00 00 00 41 5d 5b c9 c3 48 89 df 48 8b b7 d8 00 00 00 48 63 f6 48 8b 57 50 48 89 f0 48 83 c0 08 48 39 c2 77 02 eb dc <48> 0f b7 5e 00 4c 0f bf eb 48 81 fb 0f ff 07 00 74 00 48 c1 e3 20
> RSP: 0018:ffffc900031f7980 EFLAGS: 00010292
> RAX: 000000002aebd048 RBX: 0000000000000000 RCX: ffff888076a99e00
> RDX: ffff88802aebd050 RSI: 000000002aebd040 RDI: ffff8880226b4b40
> RBP: ffffc900031f7990 R08: ffffffff8183cf51 R09: 1ffffffff1f5b295
> R10: dffffc0000000000 R11: ffffffffa0001f9c R12: ffffffff8998404e
> R13: dffffc0000000000 R14: ffffc90000ace030 R15: ffffc90000ace020
> FS:  0000555562a39380(0000) GS:ffff8880b9400000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000000002aebd040 CR3: 0000000021bc0000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>   <TASK>
>   bpf_dispatcher_nop_func include/linux/bpf.h:1243 [inline]
>   __bpf_prog_run include/linux/filter.h:691 [inline]
>   bpf_prog_run include/linux/filter.h:698 [inline]
>   bpf_test_run+0x409/0x910 net/bpf/test_run.c:425
>   bpf_prog_test_run_skb+0xafa/0x13a0 net/bpf/test_run.c:1072
>   bpf_prog_test_run+0x33a/0x3b0 kernel/bpf/syscall.c:4292
>   __sys_bpf+0x48d/0x810 kernel/bpf/syscall.c:5706
>   __do_sys_bpf kernel/bpf/syscall.c:5795 [inline]
>   __se_sys_bpf kernel/bpf/syscall.c:5793 [inline]
>   __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5793
>   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: 0033:0x7fcd7dc9bbb9
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 c1 17 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 b8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ffc1893ff98 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fcd7dc9bbb9
> RDX: 000000000000004c RSI: 0000000020000240 RDI: 000000000000000a
> RBP: 0000000000000000 R08: 0000000000000006 R09: 0000000000000006
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000001
>   </TASK>
> Modules linked in:
> CR2: 000000002aebd040
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:bpf_prog_82ec301e76077160+0x5c/0xa0
> Code: 0a b8 02 00 00 00 41 5d 5b c9 c3 48 89 df 48 8b b7 d8 00 00 00 48 63 f6 48 8b 57 50 48 89 f0 48 83 c0 08 48 39 c2 77 02 eb dc <48> 0f b7 5e 00 4c 0f bf eb 48 81 fb 0f ff 07 00 74 00 48 c1 e3 20
> RSP: 0018:ffffc900031f7980 EFLAGS: 00010292
> RAX: 000000002aebd048 RBX: 0000000000000000 RCX: ffff888076a99e00
> RDX: ffff88802aebd050 RSI: 000000002aebd040 RDI: ffff8880226b4b40
> RBP: ffffc900031f7990 R08: ffffffff8183cf51 R09: 1ffffffff1f5b295
> R10: dffffc0000000000 R11: ffffffffa0001f9c R12: ffffffff8998404e
> R13: dffffc0000000000 R14: ffffc90000ace030 R15: ffffc90000ace020
> FS:  0000555562a39380(0000) GS:ffff8880b9400000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000000002aebd040 CR3: 0000000021bc0000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> ----------------
> Code disassembly (best guess):
>     0:	0a b8 02 00 00 00    	or     0x2(%rax),%bh
>     6:	41 5d                	pop    %r13
>     8:	5b                   	pop    %rbx
>     9:	c9                   	leave
>     a:	c3                   	ret
>     b:	48 89 df             	mov    %rbx,%rdi
>     e:	48 8b b7 d8 00 00 00 	mov    0xd8(%rdi),%rsi
>    15:	48 63 f6             	movslq %esi,%rsi
>    18:	48 8b 57 50          	mov    0x50(%rdi),%rdx
>    1c:	48 89 f0             	mov    %rsi,%rax
>    1f:	48 83 c0 08          	add    $0x8,%rax
>    23:	48 39 c2             	cmp    %rax,%rdx
>    26:	77 02                	ja     0x2a
>    28:	eb dc                	jmp    0x6
> * 2a:	48 0f b7 5e 00       	movzwq 0x0(%rsi),%rbx <-- trapping instruction
>    2f:	4c 0f bf eb          	movswq %bx,%r13
>    33:	48 81 fb 0f ff 07 00 	cmp    $0x7ff0f,%rbx
>    3a:	74 00                	je     0x3c
>    3c:	48 c1 e3 20          	shl    $0x20,%rbx
>
>
> ---
> 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 syzkaller@xxxxxxxxxxxxxxxx.
>
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> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
>
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>
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The failure is due to the following bpf code:
        r2 = *(s32 *)(r1 + 76)  /* __sk_buff->data */
        r3 = *(u32 *)(r1 + 80)  /* __sk_buff->data_end */
        r0 = r2
        r0 += 8
        if r3 > r0 goto +1

After verification:
        r2 = *(u64 *)(r1 +208)
        r2 = (s32)r2    /* added in convert_ctx_accesses() */
        r3 = *(u64 *)(r1 +80)
        r0 = r2
        r0 += 8
        if r3 > r0 goto pc+1

The 'r2 = (s32)r2' will cause incorrect __sk_buff->data.
I will send a patch shortly.