[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. 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
