--- /dev/null
+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
--- /dev/null
+/*
+ * 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");
projects / GitHub / moto-9609 / android_kernel_motorola_exynos9610.git / commitdiff