CVE-2023-52771 Information

Description

In the Linux kernel the following vulnerability has been resolved:

cxl/port: Fix delete_endpoint() vs parent unregistration race

The CXL subsystem at cxl_mem ->probe() time establishes a lineage of ports (struct cxl_port objects) between an endpoint and the root of a CXL topology. Each port including the endpoint port is attached to the cxl_port driver.

Given that setup it follows that when either any port in that lineage goes through a cxl_port ->remove() event or the memdev goes through a cxl_mem ->remove() event. The hierarchy below the removed port or the entire hierarchy if the memdev is removed needs to come down.

The delete_endpoint() callback is careful to check whether it is being called to tear down the hierarchy or if it is only being called to teardown the memdev because an ancestor port is going through ->remove().

That care needs to take the device_lock() of the endpoint’s parent. Which requires 2 bugs to be fixed:

1/ A reference on the parent is needed to prevent use-after-free scenarios like this signature:

BUG: spinlock bad magic on CPU0 kworker/u56:0/11
Hardware name: QEMU Standard PC (Q35 + ICH9 2009) BIOS edk2-20230524-3.fc38 05/24/2023
Workqueue: cxl_port detach_memdev [cxl_core]
RIP: 0010:spin_bug+0x65/0xa0
Call Trace:
  do_raw_spin_lock+0x69/0xa0
 __mutex_lock+0x695/0xb80
 delete_endpoint+0xad/0x150 [cxl_core]
 devres_release_all+0xb8/0x110
 device_unbind_cleanup+0xe/0x70
 device_release_driver_internal+0x1d2/0x210
 detach_memdev+0x15/0x20 [cxl_core]
 process_one_work+0x1e3/0x4c0
 worker_thread+0x1dd/0x3d0

2/ In the case of RCH topologies the parent device that needs to be locked is not always @port->dev as returned by cxl_mem_find_port() use endpoint->dev.parent instead.

Reference

https://git.kernel.org/stable/c/37179fcc916bce8c3cc7b36d67ef814cce55142b https://git.kernel.org/stable/c/6b2e428e673b3f55965674a426c40922e91388aa https://git.kernel.org/stable/c/8d2ad999ca3c64cb08cf6a58d227b9d9e746d708