On 2021-11-05 03:35, Yuan, Perry wrote: > [AMD Official Use Only] > > Hi Jani: > > >> -----Original Message----- >> From: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx> >> Sent: Wednesday, November 3, 2021 7:31 PM >> To: Yuan, Perry <Perry.Yuan@xxxxxxx>; Maarten Lankhorst >> <maarten.lankhorst@xxxxxxxxxxxxxxx>; Maxime Ripard >> <mripard@xxxxxxxxxx>; Thomas Zimmermann <tzimmermann@xxxxxxx>; >> David Airlie <airlied@xxxxxxxx>; Daniel Vetter <daniel@xxxxxxxx> >> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Huang, >> Shimmer <Xinmei.Huang@xxxxxxx>; Huang, Ray <Ray.Huang@xxxxxxx> >> Subject: RE: [PATCH v2] drm/dp: Fix aux->transfer NULL pointer dereference >> on drm_dp_dpcd_access >> >> [CAUTION: External Email] >> >> On Wed, 03 Nov 2021, "Yuan, Perry" <Perry.Yuan@xxxxxxx> wrote: >>> [AMD Official Use Only] >>> >>> Hi Jani: >>> >>>> -----Original Message----- >>>> From: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx> >>>> Sent: Tuesday, November 2, 2021 4:40 PM >>>> To: Yuan, Perry <Perry.Yuan@xxxxxxx>; Maarten Lankhorst >>>> <maarten.lankhorst@xxxxxxxxxxxxxxx>; Maxime Ripard >>>> <mripard@xxxxxxxxxx>; Thomas Zimmermann <tzimmermann@xxxxxxx>; >> David >>>> Airlie <airlied@xxxxxxxx>; Daniel Vetter <daniel@xxxxxxxx> >>>> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; >>>> Huang, Shimmer <Xinmei.Huang@xxxxxxx>; Huang, Ray >> <Ray.Huang@xxxxxxx> >>>> Subject: RE: [PATCH v2] drm/dp: Fix aux->transfer NULL pointer >>>> dereference on drm_dp_dpcd_access >>>> >>>> [CAUTION: External Email] >>>> >>>> On Tue, 02 Nov 2021, "Yuan, Perry" <Perry.Yuan@xxxxxxx> wrote: >>>>> [AMD Official Use Only] >>>>> >>>>> Hi Jani: >>>>> Thanks for your comments. >>>>> >>>>>> -----Original Message----- >>>>>> From: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx> >>>>>> Sent: Monday, November 1, 2021 9:07 PM >>>>>> To: Yuan, Perry <Perry.Yuan@xxxxxxx>; Maarten Lankhorst >>>>>> <maarten.lankhorst@xxxxxxxxxxxxxxx>; Maxime Ripard >>>>>> <mripard@xxxxxxxxxx>; Thomas Zimmermann >> <tzimmermann@xxxxxxx>; >>>> David >>>>>> Airlie <airlied@xxxxxxxx>; Daniel Vetter <daniel@xxxxxxxx> >>>>>> Cc: Yuan, Perry <Perry.Yuan@xxxxxxx>; >>>>>> dri-devel@xxxxxxxxxxxxxxxxxxxxx; linux- kernel@xxxxxxxxxxxxxxx; >>>>>> Huang, Shimmer <Xinmei.Huang@xxxxxxx>; Huang, Ray >>>> <Ray.Huang@xxxxxxx> >>>>>> Subject: Re: [PATCH v2] drm/dp: Fix aux->transfer NULL pointer >>>>>> dereference on drm_dp_dpcd_access >>>>>> >>>>>> [CAUTION: External Email] >>>>>> >>>>>> On Mon, 01 Nov 2021, Perry Yuan <Perry.Yuan@xxxxxxx> wrote: >>>>>>> Fix below crash by adding a check in the drm_dp_dpcd_access >>>>>>> which ensures that aux->transfer was actually initialized earlier. >>>>>> >>>>>> Gut feeling says this is papering over a real usage issue >>>>>> somewhere else. Why is the aux being used for transfers before >>>>>> ->transfer has been set? Why should the dp helper be defensive >>>>>> against all kinds of >>>> misprogramming? >>>>>> >>>>>> >>>>>> BR, >>>>>> Jani. >>>>>> >>>>> >>>>> The issue was found by Intel IGT test suite, graphic by pass test case. >>>>> >> https://g itl >>>>> ab.freedesktop.org%2Fdrm%2Figt-gpu- >>>> tools&data=04%7C01%7CPerry.Yuan >>>>> %40amd.com%7C83d011acfe65437c0fa808d99ddc65b0%7C3dd8961fe4 >> 884e6 >>>> 08e11a8 >>>>> >>>> >> 2d994e183d%7C0%7C0%7C637714392203200313%7CUnknown%7CTWFpbG >> Zsb >>>> 3d8eyJWIj >>>>> >>>> >> oiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1 >> 00 >>>> 0&am >>>>> >>>> >> p;sdata=snPpRYLGeJtTpNGle1YHZAvevcABbgLkgOsffiNzQPw%3D&reser >> ved >>>> =0 >>>>> normally use case will not see the issue. >>>>> To avoid this issue happy again when we run the test case , it will >>>>> be nice to >>>> add a check before the transfer is called. >>>>> And we can see that it really needs to have a check here to make >>>>> ITG &kernel >>>> happy. >>>> >>>> You're missing my point. What is the root cause? Why do you have the >>>> aux device or connector registered before ->transfer function is >>>> initialized. I don't think you should do that. >>>> >>>> BR, >>>> Jani. >>>> >>> >>> One potential IGT fix patch to resolve the test case failure is: >>> >>> tests/amdgpu/amd_bypass.c >>> data->pipe_crc = igt_pipe_crc_new(data->drm_fd, data->pipe_id, >>> - AMDGPU_PIPE_CRC_SOURCE_DPRX); >>> + INTEL_PIPE_CRC_SOURCE_AUTO); >>> The kernel panic error gone after change "dprx" to "auto" in the IGT test. >>> >>> In my view ,the IGT amdgpu bypass test will do some common setup work >> including crc piple, source. >>> When the IGT sets up a new CRC pipe capture source for amdgpu bypass >> test, the SOURCE was set as "dprx" instead of "auto" >>> It makes "amdgpu_dm_crtc_set_crc_source()" failed to set correct AUX >> and it's transfer function invalid . >>> The system I tested use HDMI port connected to monitor . >>> >>> amdgpu_dm_crtc_set_crc_source-> (aux = (aconn->port) ? &aconn- >>> port->aux : &aconn->dm_dp_aux.aux;) >>> drm_dp_start_crc -> >>> drm_dp_dpcd_readb-> aux->transfer is NULL, issue here. >>> The fix will use the "auto" keyword, which will let the driver select a >> default source of frame CRCs for this CRTC. >>> >>> Correct me if have some wrong points. >> >> Apparently I'm completely failing to communicate my POV to you. >> >> If you have a kernel oops, the fix needs to be in the kernel, not IGT. >> >> The question is, why is it possible for IGT (or any userspace) to trigger AUX >> communication when the ->transfer function is not set? In my opinion, the >> kernel driver should not have exposed the interface at all if the ->transfer >> function is not set. The interface is useless without the ->transfer function. >> IMO, that's the bug. >> > > Yes , you are correct , the transfer shouldn't be called before it is ready ! > > Let me explain more details in my view . > Maybe the root cause is not why the aux->transfer is not called before it is registered in this case. > I suppose the issue was triggered by wrong CRC pipe source . > > Actually the aux->transfer has been registered when amdgpu DM registered at kernel boot. > IGT test was run when system login to Gnome desktop. > > amdgpu_dm_initialize_dp_connector-> > aconnector->dm_dp_aux.aux.transfer = dm_dp_aux_transfer; > > The test case failed when the IGT set an "DPRX" CRC pipe source while the HDMI connected to monitor only. > At this time, the aux->transfer is NULL, and dp helper did not check the transfer pointer NULL or not. > It calls the transfers to DPCD read, then you see the kernel panic log. > > amdgpu_dm_crtc_funcs-> amdgpu_dm_crtc_set_crc_source-> drm_dp_start_crc > > * And if the DP cable connected only, the issue will not happen. Test will pass. > * If I change the CRC source to "auto", kernel will not see the panic as well. > Maybe the failed test case need to run on the DP instead of HDMI, I am not sure at now. > Two things need to happen: 1) IGT should skip tests requiring DPRX CRC source if not on a DP connector. 2) Driver should return EINVAL (or another appropriate error) if DPRX CRC source is requested when the CRTC is not connected to a DP display. Alternatively we could make sure that DPRX is not advertised as a CRC source in this case but I'm not sure how difficult that would be. Like Jani said, I don't think the current patch is the correct one as it doesn't get to the root cause. The root cause fix should be in the CRC debugfs handling code. Harry > > Hopping this info can help. > > Perry. > > >> >> BR, >> Jani. >> >>> >>> Thank you! >>> Perry. >>> >>>> >>>>> >>>>> Perry. >>>>> >>>>>> >>>>>>> >>>>>>> BUG: kernel NULL pointer dereference, address: 0000000000000000 >>>>>>> PGD >>>>>>> 0 P4D 0 >>>>>>> Oops: 0010 [#1] SMP NOPTI >>>>>>> RIP: 0010:0x0 >>>>>>> Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6. >>>>>>> RSP: 0018:ffffa8d64225bab8 EFLAGS: 00010246 >>>>>>> RAX: 0000000000000000 RBX: 0000000000000020 RCX: >>>>>>> ffffa8d64225bb5e >>>>>>> RDX: ffff93151d921880 RSI: ffffa8d64225bac8 RDI: >>>>>>> ffff931511a1a9d8 >>>>>>> RBP: ffffa8d64225bb10 R08: 0000000000000001 R09: >>>>>>> ffffa8d64225ba60 >>>>>>> R10: 0000000000000002 R11: 000000000000000d R12: >>>>>>> 0000000000000001 >>>>>>> R13: 0000000000000000 R14: ffffa8d64225bb5e R15: >>>>>>> ffff931511a1a9d8 >>>>>>> FS: 00007ff8ea7fa9c0(0000) GS:ffff9317fe6c0000(0000) >>>>>>> knlGS:0000000000000000 >>>>>>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>>>>>> CR2: ffffffffffffffd6 CR3: 000000010d5a4000 CR4: >>>>>>> 0000000000750ee0 >>>>>>> PKRU: 55555554 >>>>>>> Call Trace: >>>>>>> drm_dp_dpcd_access+0x72/0x110 [drm_kms_helper] >>>>>>> drm_dp_dpcd_read+0xb7/0xf0 [drm_kms_helper] >>>>>>> drm_dp_start_crc+0x38/0xb0 [drm_kms_helper] >>>>>>> amdgpu_dm_crtc_set_crc_source+0x1ae/0x3e0 [amdgpu] >>>>>>> crtc_crc_open+0x174/0x220 [drm] >>>>>>> full_proxy_open+0x168/0x1f0 >>>>>>> ? open_proxy_open+0x100/0x100 >>>>>>> do_dentry_open+0x156/0x370 >>>>>>> vfs_open+0x2d/0x30 >>>>>>> >>>>>>> v2: fix some typo >>>>>>> >>>>>>> Signed-off-by: Perry Yuan <Perry.Yuan@xxxxxxx> >>>>>>> --- >>>>>>> drivers/gpu/drm/drm_dp_helper.c | 4 ++++ >>>>>>> 1 file changed, 4 insertions(+) >>>>>>> >>>>>>> diff --git a/drivers/gpu/drm/drm_dp_helper.c >>>>>>> b/drivers/gpu/drm/drm_dp_helper.c index >>>>>>> 6d0f2c447f3b..76b28396001a >>>>>>> 100644 >>>>>>> --- a/drivers/gpu/drm/drm_dp_helper.c >>>>>>> +++ b/drivers/gpu/drm/drm_dp_helper.c >>>>>>> @@ -260,6 +260,10 @@ static int drm_dp_dpcd_access(struct >>>>>>> drm_dp_aux >>>>>> *aux, u8 request, >>>>>>> msg.buffer = buffer; >>>>>>> msg.size = size; >>>>>>> >>>>>>> + /* No transfer function is set, so not an available DP connector */ >>>>>>> + if (!aux->transfer) >>>>>>> + return -EINVAL; >>>>>>> + >>>>>>> mutex_lock(&aux->hw_mutex); >>>>>>> >>>>>>> /* >>>>>> >>>>>> -- >>>>>> Jani Nikula, Intel Open Source Graphics Center >>>> >>>> -- >>>> Jani Nikula, Intel Open Source Graphics Center >> >> -- >> Jani Nikula, Intel Open Source Graphics Center
