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.
Cc: [email protected]
Closes: https://gitlab.freedesktop.org/drm/amd/-/work_items/5689
Signed-off-by: Mario Limonciello <[email protected]>
---
.../gpu/drm/amd/amdkfd/kfd_process_queue_manager.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_process_queue_manager.c
b/drivers/gpu/drm/amd/amdkfd/kfd_process_queue_manager.c
index 9e607098c3a09..fb2d8ad9c2c5e 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_process_queue_manager.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_process_queue_manager.c
@@ -1170,13 +1170,13 @@ 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;
+ }
}
}
--
2.43.0
