cxl/pmem: Enforce keyctl ABI for PMEM security

Preclude the possibility of user tooling sending device secrets in the
clear into the kernel by marking the security commands as exclusive.
This mandates the usage of the keyctl ABI for managing the device
passphrase.
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/166993221008.1995348.11651567302609703175.stgit@dwillia2-xfh.jf.intel.comSigned-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/cxl/core/mbox.c

@@ -704,6 +704,16 @@ int cxl_enumerate_cmds(struct cxl_dev_state *cxlds)
 		rc = 0;
 	}
 
+	/*
+	 * Setup permanently kernel exclusive commands, i.e. the
+	 * mechanism is driven through sysfs, keyctl, etc...
+	 */
+	set_bit(CXL_MEM_COMMAND_ID_SET_PASSPHRASE, cxlds->exclusive_cmds);
+	set_bit(CXL_MEM_COMMAND_ID_DISABLE_PASSPHRASE, cxlds->exclusive_cmds);
+	set_bit(CXL_MEM_COMMAND_ID_UNLOCK, cxlds->exclusive_cmds);
+	set_bit(CXL_MEM_COMMAND_ID_PASSPHRASE_SECURE_ERASE,
+		cxlds->exclusive_cmds);
+
 out:
 	kvfree(gsl);
 	return rc;