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. > > 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
