evm: provide a function to set the EVM key from the kernel

A crypto HW kernel module can possibly initialize the EVM key from the
kernel __init code to enable EVM before calling the 'init' process.
This patch provides a function evm_set_key() to set the EVM key
directly without using the KEY subsystem.

Changes in v4:
* kernel-doc style for evm_set_key

Changes in v3:
* error reporting moved to evm_set_key
* EVM_INIT_HMAC moved to evm_set_key
* added bitop to prevent key setting race

Changes in v2:
* use size_t for key size instead of signed int
* provide EVM_MAX_KEY_SIZE macro in <linux/evm.h>
* provide EVM_MIN_KEY_SIZE macro in <linux/evm.h>

Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@huawei.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/include/linux/evm.h b/include/linux/evm.h
index 1fcb88ca88de..35ed9a8a403a 100644
--- a/include/linux/evm.h
+++ b/include/linux/evm.h
@@ -14,6 +14,7 @@
 struct integrity_iint_cache;
 
 #ifdef CONFIG_EVM
+extern int evm_set_key(void *key, size_t keylen);
 extern enum integrity_status evm_verifyxattr(struct dentry *dentry,
                                              const char *xattr_name,
                                              void *xattr_value,
@@ -42,6 +43,12 @@ static inline int posix_xattr_acl(const char *xattrname)
 }
 #endif
 #else
+
+static inline int evm_set_key(void *key, size_t keylen)
+{
+        return -EOPNOTSUPP;
+}
+
 #ifdef CONFIG_INTEGRITY
 static inline enum integrity_status evm_verifyxattr(struct dentry *dentry,
                                                     const char *xattr_name,