path: root/security/integrity/evm/evm.h
diff options
authorMimi Zohar <>2011-03-15 16:12:09 -0400
committerMimi Zohar <>2011-07-18 12:29:40 -0400
commit66dbc325afcef909043c30e90930a36823fc734c (patch)
tree5c8a7fe063a058f4266c6db5e48229e8c04dd00e /security/integrity/evm/evm.h
parent1601fbad2b14e0b8d4dbb55e749bfe31e972818a (diff)
evm: re-release
EVM protects a file's security extended attributes(xattrs) against integrity attacks. This patchset provides the framework and an initial method. The initial method maintains an HMAC-sha1 value across the security extended attributes, storing the HMAC value as the extended attribute 'security.evm'. Other methods of validating the integrity of a file's metadata will be posted separately (eg. EVM-digital-signatures). While this patchset does authenticate the security xattrs, and cryptographically binds them to the inode, coming extensions will bind other directory and inode metadata for more complete protection. To help simplify the review and upstreaming process, each extension will be posted separately (eg. IMA-appraisal, IMA-appraisal-directory). For a general overview of the proposed Linux integrity subsystem, refer to Dave Safford's whitepaper: EVM depends on the Kernel Key Retention System to provide it with a trusted/encrypted key for the HMAC-sha1 operation. The key is loaded onto the root's keyring using keyctl. Until EVM receives notification that the key has been successfully loaded onto the keyring (echo 1 > <securityfs>/evm), EVM can not create or validate the 'security.evm' xattr, but returns INTEGRITY_UNKNOWN. Loading the key and signaling EVM should be done as early as possible. Normally this is done in the initramfs, which has already been measured as part of the trusted boot. For more information on creating and loading existing trusted/encrypted keys, refer to Documentation/keys-trusted-encrypted.txt. A sample dracut patch, which loads the trusted/encrypted key and enables EVM, is available from Based on the LSMs enabled, the set of EVM protected security xattrs is defined at compile. EVM adds the following three calls to the existing security hooks: evm_inode_setxattr(), evm_inode_post_setxattr(), and evm_inode_removexattr. To initialize and update the 'security.evm' extended attribute, EVM defines three calls: evm_inode_post_init(), evm_inode_post_setattr() and evm_inode_post_removexattr() hooks. To verify the integrity of a security xattr, EVM exports evm_verifyxattr(). Changelog v7: - Fixed URL in EVM ABI documentation Changelog v6: (based on Serge Hallyn's review) - fix URL in patch description - remove evm_hmac_size definition - use SHA1_DIGEST_SIZE (removed both MAX_DIGEST_SIZE and evm_hmac_size) - moved linux include before other includes - test for crypto_hash_setkey failure - fail earlier for invalid key - clear entire encrypted key, even on failure - check xattr name length before comparing xattr names Changelog: - locking based on i_mutex, remove evm_mutex - using trusted/encrypted keys for storing the EVM key used in the HMAC-sha1 operation. - replaced crypto hash with shash (Dmitry Kasatkin) - support for additional methods of verifying the security xattrs (Dmitry Kasatkin) - iint not allocated for all regular files, but only for those appraised - Use cap_sys_admin in lieu of cap_mac_admin - Use __vfs_setxattr_noperm(), without permission checks, from EVM Signed-off-by: Mimi Zohar <> Acked-by: Serge Hallyn <>
Diffstat (limited to 'security/integrity/evm/evm.h')
1 files changed, 33 insertions, 0 deletions
diff --git a/security/integrity/evm/evm.h b/security/integrity/evm/evm.h
new file mode 100644
index 000000000000..375dc3e6015c
--- /dev/null
+++ b/security/integrity/evm/evm.h
@@ -0,0 +1,33 @@
+ * Copyright (C) 2005-2010 IBM Corporation
+ *
+ * Authors:
+ * Mimi Zohar <>
+ * Kylene Hall <>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 2 of the License.
+ *
+ * File: evm.h
+ *
+ */
+#include <linux/security.h>
+#include "../integrity.h"
+extern int evm_initialized;
+extern char *evm_hmac;
+/* List of EVM protected security xattrs */
+extern char *evm_config_xattrnames[];
+extern int evm_init_key(void);
+extern int evm_update_evmxattr(struct dentry *dentry,
+ const char *req_xattr_name,
+ const char *req_xattr_value,
+ size_t req_xattr_value_len);
+extern int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
+ const char *req_xattr_value,
+ size_t req_xattr_value_len, char *digest);
+extern int evm_init_secfs(void);
+extern void evm_cleanup_secfs(void);