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Message-ID: <f374e4ac-807d-48e4-b339-b785fabfa2c3@oracle.com>
Date:   Sat, 28 Oct 2023 00:01:05 +0100
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Subject: Re: [syzbot] [iommu?] divide error in iommufd_test
Content-Language: en-US
To:     iommu@lists.linux.dev, jgg@nvidia.com, jgg@ziepe.ca,
        kevin.tian@intel.com
References: <00000000000005f6aa0608b9220f@google.com>
Cc:     syzbot <syzbot+25dc7383c30ecdc83c38@syzkaller.appspotmail.com>,
        joro@8bytes.org, syzkaller-bugs@googlegroups.com,
        linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org,
        will@kernel.org, robin.murphy@arm.com, shuah@kernel.org
From:   Joao Martins <joao.m.martins@oracle.com>
In-Reply-To: <00000000000005f6aa0608b9220f@google.com>
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On 27/10/2023 22:11, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    e8361b005d7c Add linux-next specific files for 20231023
> git tree:       linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=13e4cb83680000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=75e8fc3570ec9a74
> dashboard link: https://syzkaller.appspot.com/bug?extid=25dc7383c30ecdc83c38
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=119bad5d680000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1062e393680000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/e28a7944599e/disk-e8361b00.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/7dd355dbe055/vmlinux-e8361b00.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/7b2a9050635d/bzImage-e8361b00.xz
> 
> The issue was bisected to:
> 
> commit 5e054083ce6929b567c6aadbf8bf627b0f028353
> Author: Joao Martins <joao.m.martins@oracle.com>
> Date:   Fri Oct 20 22:28:02 2023 +0000
> 
>     iommufd/selftest: Test IOMMU_HWPT_GET_DIRTY_BITMAP
> 

It is missing a !page_size check. The only divisions that occur here is to
page_size; perhaps I should find a way to reuse the check_iova_range I added,
and I don't need to replicate the same checks that I do here.

I'll follow-up on Monday.

> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=14a49a35680000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=16a49a35680000
> console output: https://syzkaller.appspot.com/x/log.txt?x=12a49a35680000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+25dc7383c30ecdc83c38@syzkaller.appspotmail.com
> Fixes: 5e054083ce69 ("iommufd/selftest: Test IOMMU_HWPT_GET_DIRTY_BITMAP")
> 
> divide error: 0000 [#1] PREEMPT SMP KASAN
> CPU: 1 PID: 5053 Comm: syz-executor178 Not tainted 6.6.0-rc6-next-20231023-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/06/2023
> RIP: 0010:iommufd_test_dirty drivers/iommu/iommufd/selftest.c:1098 [inline]
> RIP: 0010:iommufd_test+0x1fd/0x35c0 drivers/iommu/iommufd/selftest.c:1203
> Code: 04 02 48 89 4c 24 28 84 c0 74 09 3c 03 7f 05 e8 69 ac 2f fd 48 8b 04 24 31 d2 31 ff 48 8b 5c 24 20 44 8b 68 08 48 8b 44 24 28 <48> f7 f3 48 89 d5 48 89 d6 e8 85 cf d8 fc 48 85 ed 0f 85 ce 22 00
> RSP: 0018:ffffc90003937cb0 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: ffffffff84affaf2 RDI: 0000000000000000
> RBP: 000000000000000d R08: 0000000000000005 R09: 000000000000000d
> R10: 000000000000000d R11: 0000000000000000 R12: 0000000000000000
> R13: 0000000000000000 R14: ffffc90003937e40 R15: ffffc90003937e00
> FS:  00005555560d7380(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020006000 CR3: 0000000075a85000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  iommufd_fops_ioctl+0x35a/0x4e0 drivers/iommu/iommufd/main.c:404
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:871 [inline]
>  __se_sys_ioctl fs/ioctl.c:857 [inline]
>  __x64_sys_ioctl+0x18f/0x210 fs/ioctl.c:857
>  do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>  do_syscall_64+0x3f/0x110 arch/x86/entry/common.c:82
>  entry_SYSCALL_64_after_hwframe+0x62/0x6a
> RIP: 0033:0x7f5fb02172e9
> Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 00 00 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:00007ffd74d26068 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00007ffd74d26238 RCX: 00007f5fb02172e9
> RDX: 0000000020000140 RSI: 0000000000003ba0 RDI: 0000000000000003
> RBP: 00007f5fb028a610 R08: 0000000000000000 R09: 00007ffd74d26238
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
> R13: 00007ffd74d26228 R14: 0000000000000001 R15: 0000000000000001
>  </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:iommufd_test_dirty drivers/iommu/iommufd/selftest.c:1098 [inline]
> RIP: 0010:iommufd_test+0x1fd/0x35c0 drivers/iommu/iommufd/selftest.c:1203
> Code: 04 02 48 89 4c 24 28 84 c0 74 09 3c 03 7f 05 e8 69 ac 2f fd 48 8b 04 24 31 d2 31 ff 48 8b 5c 24 20 44 8b 68 08 48 8b 44 24 28 <48> f7 f3 48 89 d5 48 89 d6 e8 85 cf d8 fc 48 85 ed 0f 85 ce 22 00
> RSP: 0018:ffffc90003937cb0 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: ffffffff84affaf2 RDI: 0000000000000000
> RBP: 000000000000000d R08: 0000000000000005 R09: 000000000000000d
> R10: 000000000000000d R11: 0000000000000000 R12: 0000000000000000
> R13: 0000000000000000 R14: ffffc90003937e40 R15: ffffc90003937e00
> FS:  00005555560d7380(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020006000 CR3: 0000000075a85000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> ----------------
> Code disassembly (best guess):
>    0:	04 02                	add    $0x2,%al
>    2:	48 89 4c 24 28       	mov    %rcx,0x28(%rsp)
>    7:	84 c0                	test   %al,%al
>    9:	74 09                	je     0x14
>    b:	3c 03                	cmp    $0x3,%al
>    d:	7f 05                	jg     0x14
>    f:	e8 69 ac 2f fd       	call   0xfd2fac7d
>   14:	48 8b 04 24          	mov    (%rsp),%rax
>   18:	31 d2                	xor    %edx,%edx
>   1a:	31 ff                	xor    %edi,%edi
>   1c:	48 8b 5c 24 20       	mov    0x20(%rsp),%rbx
>   21:	44 8b 68 08          	mov    0x8(%rax),%r13d
>   25:	48 8b 44 24 28       	mov    0x28(%rsp),%rax
> * 2a:	48 f7 f3             	div    %rbx <-- trapping instruction
>   2d:	48 89 d5             	mov    %rdx,%rbp
>   30:	48 89 d6             	mov    %rdx,%rsi
>   33:	e8 85 cf d8 fc       	call   0xfcd8cfbd
>   38:	48 85 ed             	test   %rbp,%rbp
>   3b:	0f                   	.byte 0xf
>   3c:	85 ce                	test   %ecx,%esi
>   3e:	22 00                	and    (%rax),%al
> 
> 
> ---
> 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@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 bug is already fixed, 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 bug's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
> 
> If the bug is a duplicate of another bug, reply with:
> #syz dup: exact-subject-of-another-report
> 
> If you want to undo deduplication, reply with:
> #syz undup