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drm/amdkfd: fix scope of mqd_mgr dereference in pqm_debugfs_mqds

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Reading /sys/kernel/debug/kfd/mqds while a process holds an active KFD
queue triggers a NULL pointer dereference because the for loop that
calls mqd_mgr->debugfs_show_mqd() is incorrectly placed outside the
if (pqn->q) block that initializes mqd_mgr.

The queue list can contain entries where pqn->q is NULL (kernel queues
where only pqn->kq is valid). In the original code:

  if (pqn->q) {
      ...
      mqd_mgr = q->device->dqm->mqd_mgrs[mqd_type];
      size = mqd_mgr->mqd_stride(...);
  }

  for (xcc = 0; xcc < num_xccs; xcc++) {  // WRONG: outside if block
      mqd = q->mqd + size * xcc;
      r = mqd_mgr->debugfs_show_mqd(m, mqd);
  }

When iterating over a queue node where pqn->q is NULL:
1. The if (pqn->q) block is skipped
2. mqd_mgr remains uninitialized (NULL from declaration)
3. The for loop executes anyway
4. mqd_mgr->debugfs_show_mqd(m, mqd) dereferences NULL

The crash manifests as:

  BUG: kernel NULL pointer dereference, address: 0000000000000000
  #PF: supervisor instruction fetch in kernel mode
  RIP: 0010:0x0
  Call Trace:
   pqm_debugfs_mqds+0x10c/0x1d0 [amdgpu]
   kfd_debugfs_mqds_by_process+0x9b/0x110 [amdgpu]
   seq_read_iter+0x132/0x4b0
   ...

Fix by moving the for loop inside the if (pqn->q) block, so mqd_mgr
and related variables are only used when properly initialized.

Closes: https://gitlab.freedesktop.org/drm/amd/-/work_items/5689
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patch.msgid.link/20260831130051.2031435-1-mario.limonciello@amd.com
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 8bfe29d5c798940f797aa24135d2734c3ffce9de)
Cc: stable@vger.kernel.org
This commit is contained in:
Mario Limonciello 2026-08-31 08:00:51 -05:00 committed by Alex Deucher
parent f63de9054d
commit 012a026bae
1 changed files with 6 additions and 6 deletions
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12
drivers/gpu/drm/amd/amdkfd/kfd_process_queue_manager.c
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@ -1169,13 +1169,13 @@ int pqm_debugfs_mqds(struct seq_file *m, void *data)
mqd_mgr = q->device->dqm->mqd_mgrs[mqd_type];
size = mqd_mgr->mqd_stride(mqd_mgr,
&q->properties);
}
for (xcc = 0; xcc < num_xccs; xcc++) {
mqd = q->mqd + size * xcc;
r = mqd_mgr->debugfs_show_mqd(m, mqd);
if (r != 0)
break;
for (xcc = 0; xcc < num_xccs; xcc++) {
mqd = q->mqd + size * xcc;
r = mqd_mgr->debugfs_show_mqd(m, mqd);
if (r != 0)
break;
}
}
}