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SubjectRe: [PATCH 5.10.y] drm/cirrus: fix a NULL vs IS_ERR() checks
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Hi David and Daniel,

Sorry but could you please help to check this issue?
Due to the function 'drm_gem_shmem_vmap' could return ERROR pointers
which will cause the kernel crash due to 'cirrus_fb_blit_rect' only
check the pointer.

Since the related code has been refactoring in mainline, so this issue
only happened in stable 5.10.y branch.

@Greg
I think it is probably not realistic to backport the related refactoring
from mainline directly, so I just give this bugfix patch only for 5.10.y
branch.

Thanks!

On 2021/12/29 22:51, Shile Zhang wrote:
>
>
> On 2021/12/29 21:31, Greg Kroah-Hartman wrote:
>> On Wed, Dec 29, 2021 at 08:48:53AM +0800, Shile Zhang wrote:
>>>
>>>
>>> On 2021/12/28 22:39, Greg Kroah-Hartman wrote:
>>>> On Tue, Dec 28, 2021 at 10:19:30PM +0800, Shile Zhang wrote:
>>>>>
>>>>>
>>>>> On 2021/12/28 22:05, Greg Kroah-Hartman wrote:
>>>>>> On Tue, Dec 28, 2021 at 09:56:25PM +0800, Shile Zhang wrote:
>>>>>>>
>>>>>>>
>>>>>>> On 2021/12/28 21:51, Greg Kroah-Hartman wrote:
>>>>>>>> On Tue, Dec 28, 2021 at 09:25:56PM +0800, Shile Zhang wrote:
>>>>>>>>> The function drm_gem_shmem_vmap can returns error pointers as
>>>>>>>>> well,
>>>>>>>>> which could cause following kernel crash:
>>>>>>>>>
>>>>>>>>> BUG: unable to handle page fault for address: fffffffffffffffc
>>>>>>>>> PGD 1426a12067 P4D 1426a12067 PUD 1426a14067 PMD 0
>>>>>>>>> Oops: 0000 [#1] SMP NOPTI
>>>>>>>>> CPU: 12 PID: 3598532 Comm: stress-ng Kdump: loaded Not tainted
>>>>>>>>> 5.10.50.x86_64 #1
>>>>>>>>> ...
>>>>>>>>> RIP: 0010:memcpy_toio+0x23/0x50
>>>>>>>>> Code: 00 00 00 00 0f 1f 00 0f 1f 44 00 00 48 85 d2 74 28 40 f6
>>>>>>>>> c7 01 75 2b 48 83 fa 01 76 06 40 f6 c7 02 75 17 48 89 d1 48 c1
>>>>>>>>> e9 02 <f3> a5 f6 c2 02 74 02 66 a5 f6 c2 01 74 01 a4 c3 66 a5
>>>>>>>>> 48 83 ea 02
>>>>>>>>> RSP: 0018:ffffafbf8a203c68 EFLAGS: 00010216
>>>>>>>>> RAX: 0000000000000000 RBX: fffffffffffffffc RCX: 0000000000000200
>>>>>>>>> RDX: 0000000000000800 RSI: fffffffffffffffc RDI: ffffafbf82000000
>>>>>>>>> RBP: ffffafbf82000000 R08: 0000000000000002 R09: 0000000000000000
>>>>>>>>> R10: 00000000000002b5 R11: 0000000000000000 R12: 0000000000000800
>>>>>>>>> R13: ffff8a6801099300 R14: 0000000000000001 R15: 0000000000000300
>>>>>>>>> FS:  00007f4a6bc5f740(0000) GS:ffff8a8641900000(0000)
>>>>>>>>> knlGS:0000000000000000
>>>>>>>>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>>>>>>> CR2: fffffffffffffffc CR3: 00000016d3874001 CR4: 00000000003606e0
>>>>>>>>> Call Trace:
>>>>>>>>>      drm_fb_memcpy_dstclip+0x5e/0x80 [drm_kms_helper]
>>>>>>>>>      cirrus_fb_blit_rect.isra.0+0xb7/0xe0 [cirrus]
>>>>>>>>>      cirrus_pipe_update+0x9f/0xa8 [cirrus]
>>>>>>>>>      drm_atomic_helper_commit_planes+0xb8/0x220 [drm_kms_helper]
>>>>>>>>>      drm_atomic_helper_commit_tail+0x42/0x80 [drm_kms_helper]
>>>>>>>>>      commit_tail+0xce/0x130 [drm_kms_helper]
>>>>>>>>>      drm_atomic_helper_commit+0x113/0x140 [drm_kms_helper]
>>>>>>>>>      drm_client_modeset_commit_atomic+0x1c4/0x200 [drm]
>>>>>>>>>      drm_client_modeset_commit_locked+0x53/0x80 [drm]
>>>>>>>>>      drm_client_modeset_commit+0x24/0x40 [drm]
>>>>>>>>>      drm_fbdev_client_restore+0x48/0x85 [drm_kms_helper]
>>>>>>>>>      drm_client_dev_restore+0x64/0xb0 [drm]
>>>>>>>>>      drm_release+0xf2/0x110 [drm]
>>>>>>>>>      __fput+0x96/0x240
>>>>>>>>>      task_work_run+0x5c/0x90
>>>>>>>>>      exit_to_user_mode_loop+0xce/0xd0
>>>>>>>>>      exit_to_user_mode_prepare+0x6a/0x70
>>>>>>>>>      syscall_exit_to_user_mode+0x12/0x40
>>>>>>>>>      entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>>>>>>>> RIP: 0033:0x7f4a6bd82c2b
>>>>>>>>>
>>>>>>>>> Fixes: ab3e023b1b4c9 ("drm/cirrus: rewrite and modernize driver.")
>>>>>>>>>
>>>>>>>>> CC: stable@vger.kernel.org
>>>>>>>>> Reported-by: Wen Kang <kw01107137@alibaba-inc.com>
>>>>>>>>> Signed-off-by: Shile Zhang <shile.zhang@linux.alibaba.com>
>>>>>>>>> ---
>>>>>>>>>      drivers/gpu/drm/tiny/cirrus.c | 2 +-
>>>>>>>>>      1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>>>
>>>>>>>> What is the git commit id of this patch in Linus's tree?
>>>>>>>
>>>>>>> Sorry, I checked that this issue seems fixed by the improvement
>>>>>>> in following
>>>>>>> series:
>>>>>>> https://patchwork.freedesktop.org/series/82217/
>>>>>>
>>>>>> I do not understand, that is a huge patch series.  What individual
>>>>>> commit in Linus's tree resolves this?
>>>>>
>>>>> Sorry,
>>>>> 1. This crash only happened in 5.10.y tree now, which fixed in
>>>>> Linus's tree
>>>>> by refactoring in above huge series.
>>>>
>>>> Which specific patch resolved the issue?
>>>>
>>>>> 2. It's hard to get the individual commit to fix this issue from that
>>>>> series. So I try to send this simple fix help to fix only for
>>>>> 5.10.y, which
>>>>> is needless to Linus's tree.
>>>>
>>>> 'git bisect' should be able to help you out.
>>>
>>> Thanks for your guidance!
>>>
>>>>
>>>>> 3. If this patch is not OK for stable tree, Could you please help to
>>>>> backport the correct fix from Linus's tree in next version of 5.10.y?
>>>>
>>>> If you can provide the commit id of the fix, sure.
>>>
>>> Thanks!
>>> I think it is this commit, which refactor the drm_gem_shmem_vmap
>>> makes the
>>> pointer returned by new added parameter.
>>> https://github.com/torvalds/linux/commit/49a3f51dfeeecb52c5aa28c5cb9592fe5e39bf95
>>>
>>
>> Have you tested it to be sure?  If so, can you please provide a
>> backported version that works?  As-is, it does not apply at all.
>
> Yes, we've tested that the mainline code fixed this issue.
> But sorry, I have not backported the bugfix from mainline due to that a
> huge series for code refactoring, with more dependencies an conflicts.
>
> So I just work out a simple patch help to fix the crash.
>
>>
>> Note, if this is to bit of a change for a stable tree (and I think it
>> is), your original patch might be correct, but I need some acks from the
>> subsystem maintainers before I can take such a thing.  I also need a lot
>> of documentation in the changelog text about why this is a 5.10-only
>> thing.
>
> Since the original guilty commit (ab3e023b1b4c9) merge in 5.2-rc1, and
> Thomas's refactoring series (49a3f51dfee) just merged in 5.11-rc1. So
> this issue only happened in stable 5.4 & 5.10 only.
>
> @David @Daniel
> Could you guys also help to check this crash issue?
>
> Thanks all!
>
>>
>> thanks,
>>
>> greg k-h

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