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://gitlab.freedesktop.org/drm/igt-gpu-tools > 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. > > 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
