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>
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@ -14,6 +14,7 @@
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struct integrity_iint_cache;
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#ifdef CONFIG_EVM
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extern int evm_set_key(void *key, size_t keylen);
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extern enum integrity_status evm_verifyxattr(struct dentry *dentry,
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const char *xattr_name,
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void *xattr_value,
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@ -42,6 +43,12 @@ static inline int posix_xattr_acl(const char *xattrname)
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}
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#endif
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#else
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static inline int evm_set_key(void *key, size_t keylen)
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{
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return -EOPNOTSUPP;
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}
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#ifdef CONFIG_INTEGRITY
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static inline enum integrity_status evm_verifyxattr(struct dentry *dentry,
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const char *xattr_name,
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@ -18,6 +18,7 @@
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#include <linux/module.h>
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#include <linux/crypto.h>
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#include <linux/xattr.h>
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#include <linux/evm.h>
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#include <keys/encrypted-type.h>
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#include <crypto/hash.h>
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#include "evm.h"
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@ -32,6 +33,44 @@ struct crypto_shash *hash_tfm;
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static DEFINE_MUTEX(mutex);
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#define EVM_SET_KEY_BUSY 0
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static unsigned long evm_set_key_flags;
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/**
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* evm_set_key() - set EVM HMAC key from the kernel
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* @key: pointer to a buffer with the key data
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* @size: length of the key data
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*
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* This function allows setting the EVM HMAC key from the kernel
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* without using the "encrypted" key subsystem keys. It can be used
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* by the crypto HW kernel module which has its own way of managing
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* keys.
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*
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* key length should be between 32 and 128 bytes long
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*/
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int evm_set_key(void *key, size_t keylen)
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{
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int rc;
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rc = -EBUSY;
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if (test_and_set_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags))
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goto busy;
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rc = -EINVAL;
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if (keylen > MAX_KEY_SIZE)
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goto inval;
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memcpy(evmkey, key, keylen);
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evm_initialized |= EVM_INIT_HMAC;
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pr_info("key initialized\n");
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return 0;
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inval:
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clear_bit(EVM_SET_KEY_BUSY, &evm_set_key_flags);
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busy:
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pr_err("key initialization failed\n");
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return rc;
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}
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EXPORT_SYMBOL_GPL(evm_set_key);
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static struct shash_desc *init_desc(char type)
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{
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long rc;
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@ -244,7 +283,7 @@ int evm_init_key(void)
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{
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struct key *evm_key;
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struct encrypted_key_payload *ekp;
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int rc = 0;
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int rc;
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evm_key = request_key(&key_type_encrypted, EVMKEY, NULL);
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if (IS_ERR(evm_key))
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@ -252,12 +291,9 @@ int evm_init_key(void)
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down_read(&evm_key->sem);
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ekp = evm_key->payload.data[0];
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if (ekp->decrypted_datalen > MAX_KEY_SIZE) {
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rc = -EINVAL;
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goto out;
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}
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memcpy(evmkey, ekp->decrypted_data, ekp->decrypted_datalen);
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out:
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rc = evm_set_key(ekp->decrypted_data, ekp->decrypted_datalen);
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/* burn the original key contents */
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memset(ekp->decrypted_data, 0, ekp->decrypted_datalen);
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up_read(&evm_key->sem);
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@ -62,7 +62,7 @@ static ssize_t evm_write_key(struct file *file, const char __user *buf,
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size_t count, loff_t *ppos)
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{
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char temp[80];
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int i, error;
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int i;
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if (!capable(CAP_SYS_ADMIN) || (evm_initialized & EVM_INIT_HMAC))
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return -EPERM;
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@ -78,12 +78,8 @@ static ssize_t evm_write_key(struct file *file, const char __user *buf,
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if ((sscanf(temp, "%d", &i) != 1) || (i != 1))
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return -EINVAL;
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error = evm_init_key();
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if (!error) {
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evm_initialized |= EVM_INIT_HMAC;
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pr_info("initialized\n");
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} else
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pr_err("initialization failed\n");
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evm_init_key();
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return count;
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}
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