Re: framebuffer bug (Re: general protection fault in do_syscall_64)

[Bartlomiej Zolnierkiewicz]

[ please remember to include dri-devel ML & me on fbdev issues, thank you ]

On 3/29/20 1:37 AM, Andy Lutomirski wrote:
> On Sat, Mar 28, 2020 at 12:34 PM syzbot
> <syzbot+f9b2c53f55a9270fc778@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>>
>> Hello,
>>
>> syzbot found the following crash on:
>>
>> HEAD commit:    69c5eea3 Merge branch 'parisc-5.6-2' of git://git.kernel.o..
>> git tree:       upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=14d3517be00000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=4ac76c43beddbd9
>> dashboard link: https://syzkaller.appspot.com/bug?extid=f9b2c53f55a9270fc778
>> compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15059d05e00000
>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16e5d5a3e00000
>>
>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> Reported-by: syzbot+f9b2c53f55a9270fc778@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> Hi framebuffer people-

Hi Andy,

> Somewhere in the framebuffer code is a horrible bug that spews zeros
> over kernel memory (including text, suggesting a *physical* memory
> overrun).  My suspicion is that there is insufficient validation in
> the ioctls that set font parameters.

fbdev is in the maintenance mode and no new features or drivers are
being added so syzbot reports are not for a new bugs (regressions) and
are not a priority (at least to me).

> Could someone who is actually familiar with this code take a look?

Unfortunately I'm not familiar with this part of fbdev and I have only
resources to review/merge pending fbdev patches from time to time so
any help in fixing this and other syzbot reports is welcomed.

PS fbdev is maintained through drm-misc tree so patches can also be
handled by other drm-misc maintainers in case I'm not available.

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics

> --Andy
> 
>>
>> general protection fault, probably for non-canonical address 0x1ffffffff1215a85: 0000 [#1] PREEMPT SMP KASAN
>> CPU: 1 PID: 7207 Comm: syz-executor045 Not tainted 5.6.0-rc7-syzkaller #0
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
>> RIP: 0010:__read_once_size include/linux/compiler.h:199 [inline]
>> RIP: 0010:do_syscall_64+0x5f/0x1b0 arch/x86/entry/common.c:289
>> Code: 48 c7 c7 28 d4 0a 89 e8 bf 5d b0 00 48 83 3d af 5b 0a 08 00 0f 84 58 01 00 00 fb 66 0f 1f 44 00 00 65 48 8b 1c 25 c0 1d 02 00 <48> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>> RSP: 0018:ffffc90001617f28 EFLAGS: 00010282
>> RAX: 1ffffffff1215a85 RBX: ffff888095530380 RCX: ffff888095530380
>> RDX: dffffc0000000000 RSI: 0000000000000000 RDI: ffff888095530bc4
>> RBP: 0000000000000000 R08: ffffffff817a2210 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000023
>> R13: dffffc0000000000 R14: ffffc90001617f58 R15: 0000000000000000
>> FS:  0000000001333880(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00007f87bf9aae78 CR3: 00000000a6a3f000 CR4: 00000000001406e0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> Call Trace:
>>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> RIP: 0033:0x4454e1
>> Code: 75 14 b8 23 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 64 1f fc ff c3 48 83 ec 08 e8 9a 42 00 00 48 89 04 24 b8 23 00 00 00 0f 05 <48> 8b 3c 24 48 89 c2 e8 e3 42 00 00 48 89 d0 48 83 c4 08 48 3d 01
>> RSP: 002b:00007ffd72d164b0 EFLAGS: 00000293 ORIG_RAX: 0000000000000023
>> RAX: ffffffffffffffda RBX: 000000000000000c RCX: 00000000004454e1
>> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00007ffd72d164c0
>> RBP: 00000000006dbc20 R08: 0000000000000000 R09: 0000000000000000
>> R10: 00007ffd72d164e0 R11: 0000000000000293 R12: 0000000000000000
>> R13: 00000000006dbc2c R14: 000000000000000a R15: 0000000000000000
>> Modules linked in:
>> ---[ end trace 3da67f82bf6bae14 ]---
>> RIP: 0010:__read_once_size include/linux/compiler.h:199 [inline]
>> RIP: 0010:do_syscall_64+0x5f/0x1b0 arch/x86/entry/common.c:289
>> Code: 48 c7 c7 28 d4 0a 89 e8 bf 5d b0 00 48 83 3d af 5b 0a 08 00 0f 84 58 01 00 00 fb 66 0f 1f 44 00 00 65 48 8b 1c 25 c0 1d 02 00 <48> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>> RSP: 0018:ffffc90001617f28 EFLAGS: 00010282
>> RAX: 1ffffffff1215a85 RBX: ffff888095530380 RCX: ffff888095530380
>> RDX: dffffc0000000000 RSI: 0000000000000000 RDI: ffff888095530bc4
>> RBP: 0000000000000000 R08: ffffffff817a2210 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000023
>> R13: dffffc0000000000 R14: ffffc90001617f58 R15: 0000000000000000
>> FS:  0000000001333880(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00007f87bf9aae78 CR3: 00000000a6a3f000 CR4: 00000000001406e0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>>
>>
>> ---
>> This bug is generated by a bot. It may contain errors.
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>> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxxx
>>
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>> syzbot can test patches for this bug, for details see:
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-- 
Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics