diff options
| -rw-r--r-- | Documentation/digsig.txt | 96 | ||||
| -rw-r--r-- | include/linux/digsig.h | 64 | ||||
| -rw-r--r-- | lib/Kconfig | 8 | ||||
| -rw-r--r-- | lib/Makefile | 1 | ||||
| -rw-r--r-- | lib/digsig.c | 284 |
5 files changed, 453 insertions, 0 deletions
diff --git a/Documentation/digsig.txt b/Documentation/digsig.txt new file mode 100644 index 00000000000..3f682889068 --- /dev/null +++ b/Documentation/digsig.txt @@ -0,0 +1,96 @@ +Digital Signature Verification API + +CONTENTS + +1. Introduction +2. API +3. User-space utilities + + +1. Introduction + +Digital signature verification API provides a method to verify digital signature. +Currently digital signatures are used by the IMA/EVM integrity protection subsystem. + +Digital signature verification is implemented using cut-down kernel port of +GnuPG multi-precision integers (MPI) library. The kernel port provides +memory allocation errors handling, has been refactored according to kernel +coding style, and checkpatch.pl reported errors and warnings have been fixed. + +Public key and signature consist of header and MPIs. + +struct pubkey_hdr { + uint8_t version; /* key format version */ + time_t timestamp; /* key made, always 0 for now */ + uint8_t algo; + uint8_t nmpi; + char mpi[0]; +} __packed; + +struct signature_hdr { + uint8_t version; /* signature format version */ + time_t timestamp; /* signature made */ + uint8_t algo; + uint8_t hash; + uint8_t keyid[8]; + uint8_t nmpi; + char mpi[0]; +} __packed; + +keyid equals to SHA1[12-19] over the total key content. +Signature header is used as an input to generate a signature. +Such approach insures that key or signature header could not be changed. +It protects timestamp from been changed and can be used for rollback +protection. + +2. API + +API currently includes only 1 function: + + digsig_verify() - digital signature verification with public key + + +/** + * digsig_verify() - digital signature verification with public key + * @keyring: keyring to search key in + * @sig: digital signature + * @sigen: length of the signature + * @data: data + * @datalen: length of the data + * @return: 0 on success, -EINVAL otherwise + * + * Verifies data integrity against digital signature. + * Currently only RSA is supported. + * Normally hash of the content is used as a data for this function. + * + */ +int digsig_verify(struct key *keyring, const char *sig, int siglen, + const char *data, int datalen); + +3. User-space utilities + +The signing and key management utilities evm-utils provide functionality +to generate signatures, to load keys into the kernel keyring. +Keys can be in PEM or converted to the kernel format. +When the key is added to the kernel keyring, the keyid defines the name +of the key: 5D2B05FC633EE3E8 in the example bellow. + +Here is example output of the keyctl utility. + +$ keyctl show +Session Keyring + -3 --alswrv 0 0 keyring: _ses +603976250 --alswrv 0 -1 \_ keyring: _uid.0 +817777377 --alswrv 0 0 \_ user: kmk +891974900 --alswrv 0 0 \_ encrypted: evm-key +170323636 --alswrv 0 0 \_ keyring: _module +548221616 --alswrv 0 0 \_ keyring: _ima +128198054 --alswrv 0 0 \_ keyring: _evm + +$ keyctl list 128198054 +1 key in keyring: +620789745: --alswrv 0 0 user: 5D2B05FC633EE3E8 + + +Dmitry Kasatkin +06.10.2011 diff --git a/include/linux/digsig.h b/include/linux/digsig.h new file mode 100644 index 00000000000..efae755017d --- /dev/null +++ b/include/linux/digsig.h @@ -0,0 +1,64 @@ +/* + * Copyright (C) 2011 Nokia Corporation + * Copyright (C) 2011 Intel Corporation + * + * Author: + * Dmitry Kasatkin <dmitry.kasatkin@nokia.com> + * <dmitry.kasatkin@intel.com> + * + * 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. + * + */ + +#ifndef _DIGSIG_H +#define _DIGSIG_H + +#include <linux/key.h> + +enum pubkey_algo { + PUBKEY_ALGO_RSA, + PUBKEY_ALGO_MAX, +}; + +enum digest_algo { + DIGEST_ALGO_SHA1, + DIGEST_ALGO_SHA256, + DIGEST_ALGO_MAX +}; + +struct pubkey_hdr { + uint8_t version; /* key format version */ + time_t timestamp; /* key made, always 0 for now */ + uint8_t algo; + uint8_t nmpi; + char mpi[0]; +} __packed; + +struct signature_hdr { + uint8_t version; /* signature format version */ + time_t timestamp; /* signature made */ + uint8_t algo; + uint8_t hash; + uint8_t keyid[8]; + uint8_t nmpi; + char mpi[0]; +} __packed; + +#if defined(CONFIG_DIGSIG) || defined(CONFIG_DIGSIG_MODULE) + +int digsig_verify(struct key *keyring, const char *sig, int siglen, + const char *digest, int digestlen); + +#else + +static inline int digsig_verify(struct key *keyring, const char *sig, + int siglen, const char *digest, int digestlen) +{ + return -EOPNOTSUPP; +} + +#endif /* CONFIG_DIGSIG */ + +#endif /* _DIGSIG_H */ diff --git a/lib/Kconfig b/lib/Kconfig index d411de53be4..c1a89185fe6 100644 --- a/lib/Kconfig +++ b/lib/Kconfig @@ -293,4 +293,12 @@ config MPILIB_EXTRA This code in unnecessary for RSA digital signature verification, and can be compiled if needed. +config DIGSIG + tristate "In-kernel signature checker" + depends on CRYPTO + select MPILIB + help + Digital signature verification. Currently only RSA is supported. + Implementation is done using GnuPG MPI library + endmenu diff --git a/lib/Makefile b/lib/Makefile index 6ba8cbf4c72..0f5cff267af 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -116,6 +116,7 @@ obj-$(CONFIG_CPU_RMAP) += cpu_rmap.o obj-$(CONFIG_CORDIC) += cordic.o obj-$(CONFIG_MPILIB) += mpi/ +obj-$(CONFIG_DIGSIG) += digsig.o hostprogs-y := gen_crc32table clean-files := crc32table.h diff --git a/lib/digsig.c b/lib/digsig.c new file mode 100644 index 00000000000..fd2402f67f8 --- /dev/null +++ b/lib/digsig.c @@ -0,0 +1,284 @@ +/* + * Copyright (C) 2011 Nokia Corporation + * Copyright (C) 2011 Intel Corporation + * + * Author: + * Dmitry Kasatkin <dmitry.kasatkin@nokia.com> + * <dmitry.kasatkin@intel.com> + * + * 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: sign.c + * implements signature (RSA) verification + * pkcs decoding is based on LibTomCrypt code + */ + +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include <linux/err.h> +#include <linux/module.h> +#include <linux/slab.h> +#include <linux/key.h> +#include <linux/crypto.h> +#include <crypto/hash.h> +#include <crypto/sha.h> +#include <keys/user-type.h> +#include <linux/mpi.h> +#include <linux/digsig.h> + +static struct crypto_shash *shash; + +static int pkcs_1_v1_5_decode_emsa(const unsigned char *msg, + unsigned long msglen, + unsigned long modulus_bitlen, + unsigned char *out, + unsigned long *outlen, + int *is_valid) +{ + unsigned long modulus_len, ps_len, i; + int result; + + /* default to invalid packet */ + *is_valid = 0; + + modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0); + + /* test message size */ + if ((msglen > modulus_len) || (modulus_len < 11)) + return -EINVAL; + + /* separate encoded message */ + if ((msg[0] != 0x00) || (msg[1] != (unsigned char)1)) { + result = -EINVAL; + goto bail; + } + + for (i = 2; i < modulus_len - 1; i++) + if (msg[i] != 0xFF) + break; + + /* separator check */ + if (msg[i] != 0) { + /* There was no octet with hexadecimal value 0x00 + to separate ps from m. */ + result = -EINVAL; + goto bail; + } + + ps_len = i - 2; + + if (*outlen < (msglen - (2 + ps_len + 1))) { + *outlen = msglen - (2 + ps_len + 1); + result = -EOVERFLOW; + goto bail; + } + + *outlen = (msglen - (2 + ps_len + 1)); + memcpy(out, &msg[2 + ps_len + 1], *outlen); + + /* valid packet */ + *is_valid = 1; + result = 0; +bail: + return result; +} + +/* + * RSA Signature verification with public key + */ +static int digsig_verify_rsa(struct key *key, + const char *sig, int siglen, + const char *h, int hlen) +{ + int err = -EINVAL; + unsigned long len; + unsigned long mlen, mblen; + unsigned nret, l; + int valid, head, i; + unsigned char *out1 = NULL, *out2 = NULL; + MPI in = NULL, res = NULL, pkey[2]; + uint8_t *p, *datap, *endp; + struct user_key_payload *ukp; + struct pubkey_hdr *pkh; + + down_read(&key->sem); + ukp = key->payload.data; + pkh = (struct pubkey_hdr *)ukp->data; + + if (pkh->version != 1) + goto err1; + + if (pkh->algo != PUBKEY_ALGO_RSA) + goto err1; + + if (pkh->nmpi != 2) + goto err1; + + datap = pkh->mpi; + endp = datap + ukp->datalen; + + for (i = 0; i < pkh->nmpi; i++) { + unsigned int remaining = endp - datap; + pkey[i] = mpi_read_from_buffer(datap, &remaining); + datap += remaining; + } + + mblen = mpi_get_nbits(pkey[0]); + mlen = (mblen + 7)/8; + + err = -ENOMEM; + + out1 = kzalloc(mlen, GFP_KERNEL); + if (!out1) + goto err; + + out2 = kzalloc(mlen, GFP_KERNEL); + if (!out2) + goto err; + + nret = siglen; + in = mpi_read_from_buffer(sig, &nret); + if (!in) + goto err; + + res = mpi_alloc(mpi_get_nlimbs(in) * 2); + if (!res) + goto err; + + err = mpi_powm(res, in, pkey[1], pkey[0]); + if (err) + goto err; + + if (mpi_get_nlimbs(res) * BYTES_PER_MPI_LIMB > mlen) { + err = -EINVAL; + goto err; + } + + p = mpi_get_buffer(res, &l, NULL); + if (!p) { + err = -EINVAL; + goto err; + } + + len = mlen; + head = len - l; + memset(out1, 0, head); + memcpy(out1 + head, p, l); + + err = -EINVAL; + pkcs_1_v1_5_decode_emsa(out1, len, mblen, out2, &len, &valid); + + if (valid && len == hlen) + err = memcmp(out2, h, hlen); + +err: + mpi_free(in); + mpi_free(res); + kfree(out1); + kfree(out2); + mpi_free(pkey[0]); + mpi_free(pkey[1]); +err1: + up_read(&key->sem); + + return err; +} + +/** + * digsig_verify() - digital signature verification with public key + * @keyring: keyring to search key in + * @sig: digital signature + * @sigen: length of the signature + * @data: data + * @datalen: length of the data + * @return: 0 on success, -EINVAL otherwise + * + * Verifies data integrity against digital signature. + * Currently only RSA is supported. + * Normally hash of the content is used as a data for this function. + * + */ +int digsig_verify(struct key *keyring, const char *sig, int siglen, + const char *data, int datalen) +{ + int err = -ENOMEM; + struct signature_hdr *sh = (struct signature_hdr *)sig; + struct shash_desc *desc = NULL; + unsigned char hash[SHA1_DIGEST_SIZE]; + struct key *key; + char name[20]; + + if (siglen < sizeof(*sh) + 2) + return -EINVAL; + + if (sh->algo != PUBKEY_ALGO_RSA) + return -ENOTSUPP; + + sprintf(name, "%llX", __be64_to_cpup((uint64_t *)sh->keyid)); + + if (keyring) { + /* search in specific keyring */ + key_ref_t kref; + kref = keyring_search(make_key_ref(keyring, 1UL), + &key_type_user, name); + if (IS_ERR(kref)) + key = ERR_PTR(PTR_ERR(kref)); + else + key = key_ref_to_ptr(kref); + } else { + key = request_key(&key_type_user, name, NULL); + } + if (IS_ERR(key)) { + pr_err("key not found, id: %s\n", name); + return PTR_ERR(key); + } + + desc = kzalloc(sizeof(*desc) + crypto_shash_descsize(shash), + GFP_KERNEL); + if (!desc) + goto err; + + desc->tfm = shash; + desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP; + + crypto_shash_init(desc); + crypto_shash_update(desc, data, datalen); + crypto_shash_update(desc, sig, sizeof(*sh)); + crypto_shash_final(desc, hash); + + kfree(desc); + + /* pass signature mpis address */ + err = digsig_verify_rsa(key, sig + sizeof(*sh), siglen - sizeof(*sh), + hash, sizeof(hash)); + +err: + key_put(key); + + return err ? -EINVAL : 0; +} +EXPORT_SYMBOL_GPL(digsig_verify); + +static int __init digsig_init(void) +{ + shash = crypto_alloc_shash("sha1", 0, 0); + if (IS_ERR(shash)) { + pr_err("shash allocation failed\n"); + return PTR_ERR(shash); + } + + return 0; + +} + +static void __exit digsig_cleanup(void) +{ + crypto_free_shash(shash); +} + +module_init(digsig_init); +module_exit(digsig_cleanup); + +MODULE_LICENSE("GPL"); |