CVE-2023-54323

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

cxl/pmem: Fix nvdimm registration races

A loop of the form:

while true; do modprobe cxl_pci; modprobe -r cxl_pci; done

...fails with the following crash signature:

BUG: kernel NULL pointer dereference, address: 0000000000000040
[..]
RIP: 0010:cxl_internal_send_cmd+0x5/0xb0 [cxl_core]
[..]
Call Trace:
 <TASK>
 cxl_pmem_ctl+0x121/0x240 [cxl_pmem]
 nvdimm_get_config_data+0xd6/0x1a0 [libnvdimm]
 nd_label_data_init+0x135/0x7e0 [libnvdimm]
 nvdimm_probe+0xd6/0x1c0 [libnvdimm]
 nvdimm_bus_probe+0x7a/0x1e0 [libnvdimm]
 really_probe+0xde/0x380
 __driver_probe_device+0x78/0x170
 driver_probe_device+0x1f/0x90
 __device_attach_driver+0x85/0x110
 bus_for_each_drv+0x7d/0xc0
 __device_attach+0xb4/0x1e0
 bus_probe_device+0x9f/0xc0
 device_add+0x445/0x9c0
 nd_async_device_register+0xe/0x40 [libnvdimm]
 async_run_entry_fn+0x30/0x130

...namely that the bottom half of async nvdimm device registration runs after the CXL has already torn down the context that cxlpmemctl() needs. Unlike the ACPI NFIT case that benefits from launching multiple nvdimm device registrations in parallel from those listed in the table, CXL is already marked PROBEPREFERASYNCHRONOUS. So provide for a synchronous registration path to preclude this scenario.