Re: [PATCH] cxl/pmem: Format nvdimm serial numbers as decimal

["Dan Williams (nvidia)" <djbw@kernel.org>]

Alison Schofield wrote:
> The CXL NVDIMM security passphrase key is looked up by the description
> "nvdimm:" followed by the device serial string. For serial numbers of
> 10 and above, the kernel auto-unlock path fails to find the key
> because ndctl names it with a decimal serial and the kernel uses hex.
> 
> That means a passphrase-protected device cannot be unlocked after a
> reboot, and the pmem namespaces it backs do not come up. Devices
> without an enrolled passphrase are unaffected.
> 
> The mismatch occurs for any serial number of 10 and above. Since CXL
> device serial numbers are vendor-assigned 64-bit values, that covers
> essentially all real hardware once security is enabled.
> 
> The 'id' sysfs attribute is established ABI that ndctl consumes as
> decimal, so format the kernel's serial string the same way. A u64
> decimal string requires up to 20 digits plus a NUL byte, so grow
> CXL_DEV_ID_LEN to fit it.
> 
> The issue was exposed by CXL unit test cxl-security.sh when cxl_test
> mock serial numbers were recently extended to 10 and above.

Good find!

This is a good fix for folks with new kernels and old tooling, but
leaves folks with old kernels in the lurch.

Not sure of the priority of doing this additional work given it is not
clear the CXL PMEM devices with security commands ever shipped, but
userspace tooling can workaround this problem by always injecting both
an nvdimm:%llx and nvdimm:%lld formatted key descriptor.

For the kernel change:

Acked-by: Dan Williams <djbw@kernel.org>