Re: drm: GPF in drm_getcap

[David Herrmann]

Hi

On Sat, Nov 26, 2016 at 6:50 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
> On Sat, Nov 26, 2016 at 6:35 PM, David Herrmann <dh.herrmann@xxxxxxxxx> wrote:
>> Hi
>>
>> On Sat, Nov 26, 2016 at 6:17 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>>> On Fri, Sep 9, 2016 at 1:56 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>>>> Hello,
>>>>
>>>> The following program triggers GPF in drm_getcap:
>>>>
>>>> // autogenerated by syzkaller (http://github.com/google/syzkaller)
>>>> #include <fcntl.h>
>>>> #include <stddef.h>
>>>> #include <stdint.h>
>>>> #include <sys/ioctl.h>
>>>> #include <sys/stat.h>
>>>> #include <sys/syscall.h>
>>>> #include <sys/types.h>
>>>> #include <unistd.h>
>>>>
>>>> int main()
>>>> {
>>>>   int fd = open("/dev/dri/card0", O_RDONLY);
>>>>   uint64_t data[2] = {0x11, 0x80};
>>>>   ioctl(fd, 0xc010640cul /*DRM_IOCTL_GET_CAP*/, data);
>>>>   return 0;
>>>> }
>>>>
>>>>
>>>> general protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN
>>>> Modules linked in:
>>>> CPU: 1 PID: 5745 Comm: syz-executor Not tainted 4.8.0-rc5-next-20160905+ #14
>>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>>>> task: ffff8800310dc540 task.stack: ffff88003cbc0000
>>>> RIP: 0010:[<ffffffff834ca87b>]  [<ffffffff834ca87b>]
>>>> drm_getcap+0x34b/0x4f0 drivers/gpu/drm/drm_ioctl.c:260
>>>> RSP: 0018:ffff88003cbc7c28  EFLAGS: 00010202
>>>> RAX: 0000000000000058 RBX: ffff88003cbc7cf8 RCX: ffffc90001db0000
>>>> RDX: 000000000000005d RSI: ffff88003cbc7cf8 RDI: 00000000000002c0
>>>> RBP: ffff88003cbc7c50 R08: ffffed0007978fa1 R09: ffffed0007978fa0
>>>> R10: ffff88003cbc7d07 R11: ffffed0007978fa1 R12: fffffffffffffff0
>>>> R13: dffffc0000000000 R14: ffff88003bcc6850 R15: fffffffffffffff2
>>>> FS:  00007fcbf4e03700(0000) GS:ffff88003ed00000(0000) knlGS:0000000000000000
>>>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>> CR2: 00000000006dce00 CR3: 0000000066135000 CR4: 00000000000006e0
>>>> DR0: 000000000000001e DR1: 000000000000001e DR2: 0000000000000000
>>>> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
>>>> Stack:
>>>>  ffff88003c26db00 ffff88003cbc7cf8 ffffffff875a3000 ffffffff88cf0ee0
>>>>  fffffffffffffff2 ffff88003cbc7dc0 ffffffff834cb57c 000000000000e200
>>>>  1ffff10000000001 ffffffff875a1ba0 ffffffff882ae930 0000000000000010
>>>> Call Trace:
>>>>  [<ffffffff834cb57c>] drm_ioctl+0x54c/0xaf0 drivers/gpu/drm/drm_ioctl.c:728
>>>>  [<     inline     >] vfs_ioctl fs/ioctl.c:43
>>>>  [<ffffffff818a331c>] do_vfs_ioctl+0x18c/0x1080 fs/ioctl.c:675
>>>>  [<     inline     >] SYSC_ioctl fs/ioctl.c:690
>>>>  [<ffffffff818a429f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:681
>>>>  [<ffffffff86e1a8c0>] entry_SYSCALL_64_fastpath+0x23/0xc1
>>>> Code: 3c 28 00 0f 85 88 01 00 00 49 8b 44 24 10 49 39 c6 4c 8d 60 f0
>>>> 74 82 e8 64 19 10 fe 49 8d bc 24 d0 02 00 00 48 89 f8 48 c1 e8 03 <42>
>>>> 80 3c 28 00 0f 85 6f 01 00 00 4d 8b bc 24 d0 02 00 00 49 8d
>>>> RIP  [<ffffffff834ca87b>] drm_getcap+0x34b/0x4f0 drivers/gpu/drm/drm_ioctl.c:260
>>>>  RSP <ffff88003cbc7c28>
>>>> ---[ end trace c6e1afa8cd73b880 ]---
>>>>
>>>>
>>>> On commit 4affa544adb8077403893e62b9e327fcf87de6f7 (Sep 8) of linux-next.
>>>
>>> ping
>>>
>>> Still happens on 16ae16c6e5616c084168740990fc508bda6655d4 (Nov 24).
>>
>> I suspect this is because we run drm_for_each_crtc() in
>> drm_getcap(DRM_PAGE_FLIP_TARGET) on a legacy driver (meaning
>> mode_config is not initialized). @danvet, how about always
>> initializing mode_config to 0/empty/dummy?
>>
>> Dmitry, what driver do you run this on? And is CONFIG_DRM_LEGACY enabled?
>
>
> CONFIG_DRM_LEGACY is enabled.
>
> How can I understand what driver is used?
> This happens inside of qemu. This is the device:
> crw-rw---T 1 root video 226, 0 Nov 26 17:45 /dev/dri/card0

Usually by looking into `dmesg` and grepping for 'card0', or by inspecting:

    /sys/class/drm/card0/device/

or more importantly looking at the symlink:

    /sys/class/drm/card0/device/driver

Thanks
David