[PATCH v2 2/3] lib: define generic accessor functions for arch specific keystore

[Nayna Jain <nayna@linux.ibm.com>]

From: Greg Joyce <gjoyce@linux.vnet.ibm.com>

Generic kernel subsystems may rely on platform specific persistent
KeyStore to store objects containing sensitive key material. In such case,
they need to access architecture specific functions to perform read/write
operations on these variables.

Define the generic variable read/write prototypes to be implemented by
architecture specific versions. The default(weak) implementations of
these prototypes return -EOPNOTSUPP unless overridden by architecture
versions.

Signed-off-by: Greg Joyce <gjoyce@linux.vnet.ibm.com>
---
 include/linux/arch_vars.h | 23 +++++++++++++++++++++++
 lib/Makefile              |  2 +-
 lib/arch_vars.c           | 25 +++++++++++++++++++++++++
 3 files changed, 49 insertions(+), 1 deletion(-)
 create mode 100644 include/linux/arch_vars.h
 create mode 100644 lib/arch_vars.c

diff --git a/include/linux/arch_vars.h b/include/linux/arch_vars.h
new file mode 100644
index 000000000000..9c280ff9432e
--- /dev/null
+++ b/include/linux/arch_vars.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Platform variable opearations.
+ *
+ * Copyright (C) 2022 IBM Corporation
+ *
+ * These are the accessor functions (read/write) for architecture specific
+ * variables. Specific architectures can provide overrides.
+ *
+ */
+
+#include <linux/kernel.h>
+
+enum arch_variable_type {
+	ARCH_VAR_OPAL_KEY      = 0,     /* SED Opal Authentication Key */
+	ARCH_VAR_OTHER         = 1,     /* Other type of variable */
+	ARCH_VAR_MAX           = 1,     /* Maximum type value */
+};
+
+int arch_read_variable(enum arch_variable_type type, char *varname,
+		       void *varbuf, u_int *varlen);
+int arch_write_variable(enum arch_variable_type type, char *varname,
+			void *varbuf, u_int varlen);
diff --git a/lib/Makefile b/lib/Makefile
index f99bf61f8bbc..b90c4cb0dbbb 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -48,7 +48,7 @@ obj-y += bcd.o sort.o parser.o debug_locks.o random32.o \
 	 bsearch.o find_bit.o llist.o memweight.o kfifo.o \
 	 percpu-refcount.o rhashtable.o \
 	 once.o refcount.o usercopy.o errseq.o bucket_locks.o \
-	 generic-radix-tree.o
+	 generic-radix-tree.o arch_vars.o
 obj-$(CONFIG_STRING_SELFTEST) += test_string.o
 obj-y += string_helpers.o
 obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
diff --git a/lib/arch_vars.c b/lib/arch_vars.c
new file mode 100644
index 000000000000..e6f16d7d09c1
--- /dev/null
+++ b/lib/arch_vars.c
@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Platform variable operations.
+ *
+ * Copyright (C) 2022 IBM Corporation
+ *
+ * These are the accessor functions (read/write) for architecture specific
+ * variables. Specific architectures can provide overrides.
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/arch_vars.h>
+
+int __weak arch_read_variable(enum arch_variable_type type, char *varname,
+			      void *varbuf, u_int *varlen)
+{
+	return -EOPNOTSUPP;
+}
+
+int __weak arch_write_variable(enum arch_variable_type type, char *varname,
+			       void *varbuf, u_int varlen)
+{
+	return -EOPNOTSUPP;
+}
-- 
2.27.0