CVE-2024-27004

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

clk: Get runtime PM before walking tree during disable_unused

Doug reported [1] the following hung task:

INFO: task swapper/0:1 blocked for more than 122 seconds.

Not tainted 5.15.149-21875-gf795ebc40eb8 #1

"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

task:swapper/0 state:D stack: 0 pid: 1 ppid: 0 flags:0x00000008

Call trace:

__switch_to+0xf4/0x1f4

__schedule+0x418/0xb80

schedule+0x5c/0x10c

rpm_resume+0xe0/0x52c

rpm_resume+0x178/0x52c

__pm_runtime_resume+0x58/0x98

clk_pm_runtime_get+0x30/0xb0

clk_disable_unused_subtree+0x58/0x208

clk_disable_unused_subtree+0x38/0x208

clk_disable_unused_subtree+0x38/0x208

clk_disable_unused_subtree+0x38/0x208

clk_disable_unused_subtree+0x38/0x208

clk_disable_unused+0x4c/0xe4

do_one_initcall+0xcc/0x2d8

do_initcall_level+0xa4/0x148

do_initcalls+0x5c/0x9c

do_basic_setup+0x24/0x30

kernel_init_freeable+0xec/0x164

kernel_init+0x28/0x120

ret_from_fork+0x10/0x20

INFO: task kworker/u16:0:9 blocked for more than 122 seconds.

Not tainted 5.15.149-21875-gf795ebc40eb8 #1

"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

task:kworker/u16:0 state:D stack: 0 pid: 9 ppid: 2 flags:0x00000008

Workqueue: events_unbound deferred_probe_work_func

Call trace:

__switch_to+0xf4/0x1f4

__schedule+0x418/0xb80

schedule+0x5c/0x10c

schedule_preempt_disabled+0x2c/0x48

__mutex_lock+0x238/0x488

__mutex_lock_slowpath+0x1c/0x28

mutex_lock+0x50/0x74

clk_prepare_lock+0x7c/0x9c

clk_core_prepare_lock+0x20/0x44

clk_prepare+0x24/0x30

clk_bulk_prepare+0x40/0xb0

mdss_runtime_resume+0x54/0x1c8

pm_generic_runtime_resume+0x30/0x44

__genpd_runtime_resume+0x68/0x7c

genpd_runtime_resume+0x108/0x1f4

__rpm_callback+0x84/0x144

rpm_callback+0x30/0x88

rpm_resume+0x1f4/0x52c

rpm_resume+0x178/0x52c

__pm_runtime_resume+0x58/0x98

__device_attach+0xe0/0x170

device_initial_probe+0x1c/0x28

bus_probe_device+0x3c/0x9c

device_add+0x644/0x814

mipi_dsi_device_register_full+0xe4/0x170

devm_mipi_dsi_device_register_full+0x28/0x70

ti_sn_bridge_probe+0x1dc/0x2c0

auxiliary_bus_probe+0x4c/0x94

really_probe+0xcc/0x2c8

__driver_probe_device+0xa8/0x130

driver_probe_device+0x48/0x110

__device_attach_driver+0xa4/0xcc

bus_for_each_drv+0x8c/0xd8

__device_attach+0xf8/0x170

device_initial_probe+0x1c/0x28

bus_probe_device+0x3c/0x9c

deferred_probe_work_func+0x9c/0xd8

process_one_work+0x148/0x518

worker_thread+0x138/0x350

kthread+0x138/0x1e0

ret_from_fork+0x10/0x20

The first thread is walking the clk tree and calling

clk_pm_runtime_get() to power on devices required to read the clk

hardware via struct clk_ops::is_enabled(). This thread holds the clk

prepare_lock, and is trying to runtime PM resume a device, when it finds

that the device is in the process of resuming so the thread schedule()s

away waiting for the device to finish resuming before continuing. The

second thread is runtime PM resuming the same device, but the runtime

resume callback is calling clk_prepare(), trying to grab the

prepare_lock waiting on the first thread.

This is a classic ABBA deadlock. To properly fix the deadlock, we must

never runtime PM resume or suspend a device with the clk prepare_lock

held. Actually doing that is near impossible today because the global

prepare_lock would have to be dropped in the middle of the tree, the

device runtime PM resumed/suspended, and then the prepare_lock grabbed

again to ensure consistency of the clk tree topology. If anything

changes with the clk tree in the meantime, we've lost and will need to

start the operation all over again.

Luckily, most of the time we're simply incrementing or decrementing the

runtime PM count on an active device, so we don't have the chance to

schedule away with the prepare_lock held. Let's fix this immediate

problem that can be

---truncated---