CVE-2026-68437: drm/imagination: Fit paired fragment job in the correct CCCB

From: Greg Kroah-Hartman <[email protected]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

drm/imagination: Fit paired fragment job in the correct CCCB

For geometry jobs with a paired fragment job, at the moment, the
DRM scheduler's prepare_job() callback:

- checks for internal (driver) dependencies for the geometry job;
- calls into pvr_queue_get_paired_frag_job_dep() to check for external
  dependencies for the fragment job (the two jobs are submitted together
  but the common scheduler code doesn't know about it, so this needs to
  be done at this point in time);
- calls into the prepare_job() callback again, but for the fragment job,
  to check its internal dependencies as well, passing the fragment job's
  drm_sched_job and the geometry job's drm_sched_entity / pvr_queue.

The problem with the last step is that pvr_queue_prepare_job() doesn't
always take the mismatched fragment job and geometry queue into account,
in particular when checking whether there is space for the fragment
command to be submitted, so the code ends up checking for space in the
geometry (i.e. wrong) CCCB.
The rest of the nested prepare_job() callback happens to work fine at
the moment as the other internal dependencies are not relevant for a
paired fragment job.

Move the initialisation of a paired fragment job's done fence and CCCB
fence to pvr_queue_get_paired_frag_job_dep(), inferring the correct
queue from the fragment job itself.

This fixes cases where prepare_job() wrongly assumed that there was
enough space for a paired fragment job in its own CCCB, unblocking
run_job(), which then returned early without writing the full sequence
of commands to the CCCB.

The above lead to kernel warnings such as the following and potentially
job timeouts (depending on waiters on the missing commands):

  [  552.421075] WARNING: drivers/gpu/drm/imagination/pvr_cccb.c:178 at pvr_cccb_write_command_with_header+0x2c4/0x330 [powervr], CPU#2: kworker/u16:5/63
  [  552.421230] Modules linked in:
  [  552.421592] CPU: 2 UID: 0 PID: 63 Comm: kworker/u16:5 Tainted: G        W           7.0.0-rc2-gc5d053e4dccb #39 PREEMPT
  [  552.421625] Tainted: [W]=WARN
  [  552.421637] Hardware name: Texas Instruments AM625 SK (DT)
  [  552.421655] Workqueue: powervr-sched drm_sched_run_job_work [gpu_sched]
  [  552.421744] pstate: 80000005 (Nzcv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
  [  552.421766] pc : pvr_cccb_write_command_with_header+0x2c4/0x330 [powervr]
  [  552.421850] lr : pvr_queue_submit_job_to_cccb+0x57c/0xa74 [powervr]
  [  552.421923] sp : ffff800084c47650
  [  552.421936] x29: ffff800084c47740 x28: 0000000000000df8 x27: ffff800088a77000
  [  552.421979] x26: 0000000000000030 x25: ffff800084c47680 x24: 0000000000001000
  [  552.422017] x23: ffff800084c47820 x22: 1ffff00010988ecc x21: 0000000000000008
  [  552.422055] x20: 0000000000000208 x19: ffff000006ad5a88 x18: 0000000000000000
  [  552.422093] x17: 0000000020020000 x16: 0000000000020000 x15: 0000000000000000
  [  552.422130] x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
  [  552.422167] x11: 000000000000f2f2 x10: 00000000f3000000 x9 : 00000000f3f3f3f3
  [  552.422204] x8 : 00000000f2f2f200 x7 : ffff700010988ecc x6 : 0000000000000008
  [  552.422241] x5 : 0000000000000000 x4 : 1ffff0001114ee00 x3 : 0000000000000000
  [  552.422278] x2 : 0000000000000007 x1 : 0000000000000fff x0 : 000000000000002f
  [  552.422316] Call trace:
  [  552.422330]  pvr_cccb_write_command_with_header+0x2c4/0x330 [powervr] (P)
  [  552.422411]  pvr_queue_submit_job_to_cccb+0x57c/0xa74 [powervr]
  [  552.422486]  pvr_queue_run_job+0x3a4/0x990 [powervr]
  [  552.422562]  drm_sched_run_job_work+0x580/0xd48 [gpu_sched]
  [  552.422623]  process_one_work+0x520/0x1288
  [  552.422657]  worker_thread+0x3f0/0xb3c
  [  552.422679]  kthread+0x334/0x3d8
  [  552.422706]  ret_from_fork+0x10/0x20

The Linux kernel CVE team has assigned CVE-2026-68437 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.8 with commit eaf01ee5ba28b97f96a3d3eec4c5fbfb37ee4cde and fixed in 6.12.101 with commit 15a9863929206911a08b6f62de9c5da6931dbc9e
	Issue introduced in 6.8 with commit eaf01ee5ba28b97f96a3d3eec4c5fbfb37ee4cde and fixed in 6.18.42 with commit e2c29d51c0f65459ae5bbf7ccc302df4c359c473
	Issue introduced in 6.8 with commit eaf01ee5ba28b97f96a3d3eec4c5fbfb37ee4cde and fixed in 7.1.6 with commit 4ddf82c18ee4b3d14ec7fa002c4039b46c961abc
	Issue introduced in 6.8 with commit eaf01ee5ba28b97f96a3d3eec4c5fbfb37ee4cde and fixed in 7.2-rc1 with commit 4baf9e70cb756d78dd56419f8baee2978a72d0c3

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-68437
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/gpu/drm/imagination/pvr_queue.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/15a9863929206911a08b6f62de9c5da6931dbc9e
	https://git.kernel.org/stable/c/e2c29d51c0f65459ae5bbf7ccc302df4c359c473
	https://git.kernel.org/stable/c/4ddf82c18ee4b3d14ec7fa002c4039b46c961abc
	https://git.kernel.org/stable/c/4baf9e70cb756d78dd56419f8baee2978a72d0c3