lib/rsa/rsa-verify.c

   1 /*
   2  * Copyright (c) 2013, Google Inc.
   3  *
   4  * SPDX-License-Identifier:     GPL-2.0+
   5  */
   6
   7 #ifndef USE_HOSTCC
   8 #include <common.h>
   9 #include <fdtdec.h>
  10 #include <asm/types.h>
  11 #include <asm/byteorder.h>
  12 #include <asm/errno.h>
  13 #include <asm/types.h>
  14 #include <asm/unaligned.h>
  15 #else
  16 #include "fdt_host.h"
  17 #include "mkimage.h"
  18 #include <fdt_support.h>
  19 #endif
  20 #include <rsa.h>
  21 #include <sha1.h>
  22 #include <sha256.h>
  23
  24 #define UINT64_MULT32(v, multby)  (((uint64_t)(v)) * ((uint32_t)(multby)))
  25
  26 #define get_unaligned_be32(a) fdt32_to_cpu(*(uint32_t *)a)
  27 #define put_unaligned_be32(a, b) (*(uint32_t *)(b) = cpu_to_fdt32(a))
  28
  29 /**
  30  * subtract_modulus() - subtract modulus from the given value
  31  *
  32  * @key:        Key containing modulus to subtract
  33  * @num:        Number to subtract modulus from, as little endian word array
  34  */
  35 static void subtract_modulus(const struct rsa_public_key *key, uint32_t num[])
  36 {
  37         int64_t acc = 0;
  38         uint i;
  39
  40         for (i = 0; i < key->len; i++) {
  41                 acc += (uint64_t)num[i] - key->modulus[i];
  42                 num[i] = (uint32_t)acc;
  43                 acc >>= 32;
  44         }
  45 }
  46
  47 /**
  48  * greater_equal_modulus() - check if a value is >= modulus
  49  *
  50  * @key:        Key containing modulus to check
  51  * @num:        Number to check against modulus, as little endian word array
  52  * @return 0 if num < modulus, 1 if num >= modulus
  53  */
  54 static int greater_equal_modulus(const struct rsa_public_key *key,
  55                                  uint32_t num[])
  56 {
  57         uint32_t i;
  58
  59         for (i = key->len - 1; i >= 0; i--) {
  60                 if (num[i] < key->modulus[i])
  61                         return 0;
  62                 if (num[i] > key->modulus[i])
  63                         return 1;
  64         }
  65
  66         return 1;  /* equal */
  67 }
  68
  69 /**
  70  * montgomery_mul_add_step() - Perform montgomery multiply-add step
  71  *
  72  * Operation: montgomery result[] += a * b[] / n0inv % modulus
  73  *
  74  * @key:        RSA key
  75  * @result:     Place to put result, as little endian word array
  76  * @a:          Multiplier
  77  * @b:          Multiplicand, as little endian word array
  78  */
  79 static void montgomery_mul_add_step(const struct rsa_public_key *key,
  80                 uint32_t result[], const uint32_t a, const uint32_t b[])
  81 {
  82         uint64_t acc_a, acc_b;
  83         uint32_t d0;
  84         uint i;
  85
  86         acc_a = (uint64_t)a * b[0] + result[0];
  87         d0 = (uint32_t)acc_a * key->n0inv;
  88         acc_b = (uint64_t)d0 * key->modulus[0] + (uint32_t)acc_a;
  89         for (i = 1; i < key->len; i++) {
  90                 acc_a = (acc_a >> 32) + (uint64_t)a * b[i] + result[i];
  91                 acc_b = (acc_b >> 32) + (uint64_t)d0 * key->modulus[i] +
  92                                 (uint32_t)acc_a;
  93                 result[i - 1] = (uint32_t)acc_b;
  94         }
  95
  96         acc_a = (acc_a >> 32) + (acc_b >> 32);
  97
  98         result[i - 1] = (uint32_t)acc_a;
  99
 100         if (acc_a >> 32)
 101                 subtract_modulus(key, result);
 102 }
 103
 104 /**
 105  * montgomery_mul() - Perform montgomery mutitply
 106  *
 107  * Operation: montgomery result[] = a[] * b[] / n0inv % modulus
 108  *
 109  * @key:        RSA key
 110  * @result:     Place to put result, as little endian word array
 111  * @a:          Multiplier, as little endian word array
 112  * @b:          Multiplicand, as little endian word array
 113  */
 114 static void montgomery_mul(const struct rsa_public_key *key,
 115                 uint32_t result[], uint32_t a[], const uint32_t b[])
 116 {
 117         uint i;
 118
 119         for (i = 0; i < key->len; ++i)
 120                 result[i] = 0;
 121         for (i = 0; i < key->len; ++i)
 122                 montgomery_mul_add_step(key, result, a[i], b);
 123 }
 124
 125 /**
 126  * pow_mod() - in-place public exponentiation
 127  *
 128  * @key:        RSA key
 129  * @inout:      Big-endian word array containing value and result
 130  */
 131 static int pow_mod(const struct rsa_public_key *key, uint32_t *inout)
 132 {
 133         uint32_t *result, *ptr;
 134         uint i;
 135
 136         /* Sanity check for stack size - key->len is in 32-bit words */
 137         if (key->len > RSA_MAX_KEY_BITS / 32) {
 138                 debug("RSA key words %u exceeds maximum %d\n", key->len,
 139                       RSA_MAX_KEY_BITS / 32);
 140                 return -EINVAL;
 141         }
 142
 143         uint32_t val[key->len], acc[key->len], tmp[key->len];
 144         result = tmp;  /* Re-use location. */
 145
 146         /* Convert from big endian byte array to little endian word array. */
 147         for (i = 0, ptr = inout + key->len - 1; i < key->len; i++, ptr--)
 148                 val[i] = get_unaligned_be32(ptr);
 149
 150         montgomery_mul(key, acc, val, key->rr);  /* axx = a * RR / R mod M */
 151         for (i = 0; i < 16; i += 2) {
 152                 montgomery_mul(key, tmp, acc, acc); /* tmp = acc^2 / R mod M */
 153                 montgomery_mul(key, acc, tmp, tmp); /* acc = tmp^2 / R mod M */
 154         }
 155         montgomery_mul(key, result, acc, val);  /* result = XX * a / R mod M */
 156
 157         /* Make sure result < mod; result is at most 1x mod too large. */
 158         if (greater_equal_modulus(key, result))
 159                 subtract_modulus(key, result);
 160
 161         /* Convert to bigendian byte array */
 162         for (i = key->len - 1, ptr = inout; (int)i >= 0; i--, ptr++)
 163                 put_unaligned_be32(result[i], ptr);
 164         return 0;
 165 }
 166
 167 static int rsa_verify_key(const struct rsa_public_key *key, const uint8_t *sig,
 168                           const uint32_t sig_len, const uint8_t *hash,
 169                           struct checksum_algo *algo)
 170 {
 171         const uint8_t *padding;
 172         int pad_len;
 173         int ret;
 174
 175         if (!key || !sig || !hash || !algo)
 176                 return -EIO;
 177
 178         if (sig_len != (key->len * sizeof(uint32_t))) {
 179                 debug("Signature is of incorrect length %d\n", sig_len);
 180                 return -EINVAL;
 181         }
 182
 183         debug("Checksum algorithm: %s", algo->name);
 184
 185         /* Sanity check for stack size */
 186         if (sig_len > RSA_MAX_SIG_BITS / 8) {
 187                 debug("Signature length %u exceeds maximum %d\n", sig_len,
 188                       RSA_MAX_SIG_BITS / 8);
 189                 return -EINVAL;
 190         }
 191
 192         uint32_t buf[sig_len / sizeof(uint32_t)];
 193
 194         memcpy(buf, sig, sig_len);
 195
 196         ret = pow_mod(key, buf);
 197         if (ret)
 198                 return ret;
 199
 200         padding = algo->rsa_padding;
 201         pad_len = algo->pad_len - algo->checksum_len;
 202
 203         /* Check pkcs1.5 padding bytes. */
 204         if (memcmp(buf, padding, pad_len)) {
 205                 debug("In RSAVerify(): Padding check failed!\n");
 206                 return -EINVAL;
 207         }
 208
 209         /* Check hash. */
 210         if (memcmp((uint8_t *)buf + pad_len, hash, sig_len - pad_len)) {
 211                 debug("In RSAVerify(): Hash check failed!\n");
 212                 return -EACCES;
 213         }
 214
 215         return 0;
 216 }
 217
 218 static void rsa_convert_big_endian(uint32_t *dst, const uint32_t *src, int len)
 219 {
 220         int i;
 221
 222         for (i = 0; i < len; i++)
 223                 dst[i] = fdt32_to_cpu(src[len - 1 - i]);
 224 }
 225
 226 static int rsa_verify_with_keynode(struct image_sign_info *info,
 227                 const void *hash, uint8_t *sig, uint sig_len, int node)
 228 {
 229         const void *blob = info->fdt_blob;
 230         struct rsa_public_key key;
 231         const void *modulus, *rr;
 232         int ret;
 233
 234         if (node < 0) {
 235                 debug("%s: Skipping invalid node", __func__);
 236                 return -EBADF;
 237         }
 238         if (!fdt_getprop(blob, node, "rsa,n0-inverse", NULL)) {
 239                 debug("%s: Missing rsa,n0-inverse", __func__);
 240                 return -EFAULT;
 241         }
 242         key.len = fdtdec_get_int(blob, node, "rsa,num-bits", 0);
 243         key.n0inv = fdtdec_get_int(blob, node, "rsa,n0-inverse", 0);
 244         modulus = fdt_getprop(blob, node, "rsa,modulus", NULL);
 245         rr = fdt_getprop(blob, node, "rsa,r-squared", NULL);
 246         if (!key.len || !modulus || !rr) {
 247                 debug("%s: Missing RSA key info", __func__);
 248                 return -EFAULT;
 249         }
 250
 251         /* Sanity check for stack size */
 252         if (key.len > RSA_MAX_KEY_BITS || key.len < RSA_MIN_KEY_BITS) {
 253                 debug("RSA key bits %u outside allowed range %d..%d\n",
 254                       key.len, RSA_MIN_KEY_BITS, RSA_MAX_KEY_BITS);
 255                 return -EFAULT;
 256         }
 257         key.len /= sizeof(uint32_t) * 8;
 258         uint32_t key1[key.len], key2[key.len];
 259
 260         key.modulus = key1;
 261         key.rr = key2;
 262         rsa_convert_big_endian(key.modulus, modulus, key.len);
 263         rsa_convert_big_endian(key.rr, rr, key.len);
 264         if (!key.modulus || !key.rr) {
 265                 debug("%s: Out of memory", __func__);
 266                 return -ENOMEM;
 267         }
 268
 269         debug("key length %d\n", key.len);
 270         ret = rsa_verify_key(&key, sig, sig_len, hash, info->algo->checksum);
 271         if (ret) {
 272                 printf("%s: RSA failed to verify: %d\n", __func__, ret);
 273                 return ret;
 274         }
 275
 276         return 0;
 277 }
 278
 279 int rsa_verify(struct image_sign_info *info,
 280                const struct image_region region[], int region_count,
 281                uint8_t *sig, uint sig_len)
 282 {
 283         const void *blob = info->fdt_blob;
 284         /* Reserve memory for maximum checksum-length */
 285         uint8_t hash[info->algo->checksum->pad_len];
 286         int ndepth, noffset;
 287         int sig_node, node;
 288         char name[100];
 289         int ret;
 290
 291         /*
 292          * Verify that the checksum-length does not exceed the
 293          * rsa-signature-length
 294          */
 295         if (info->algo->checksum->checksum_len >
 296             info->algo->checksum->pad_len) {
 297                 debug("%s: invlaid checksum-algorithm %s for %s\n",
 298                       __func__, info->algo->checksum->name, info->algo->name);
 299                 return -EINVAL;
 300         }
 301
 302         sig_node = fdt_subnode_offset(blob, 0, FIT_SIG_NODENAME);
 303         if (sig_node < 0) {
 304                 debug("%s: No signature node found\n", __func__);
 305                 return -ENOENT;
 306         }
 307
 308         /* Calculate checksum with checksum-algorithm */
 309         info->algo->checksum->calculate(region, region_count, hash);
 310
 311         /* See if we must use a particular key */
 312         if (info->required_keynode != -1) {
 313                 ret = rsa_verify_with_keynode(info, hash, sig, sig_len,
 314                         info->required_keynode);
 315                 if (!ret)
 316                         return ret;
 317         }
 318
 319         /* Look for a key that matches our hint */
 320         snprintf(name, sizeof(name), "key-%s", info->keyname);
 321         node = fdt_subnode_offset(blob, sig_node, name);
 322         ret = rsa_verify_with_keynode(info, hash, sig, sig_len, node);
 323         if (!ret)
 324                 return ret;
 325
 326         /* No luck, so try each of the keys in turn */
 327         for (ndepth = 0, noffset = fdt_next_node(info->fit, sig_node, &ndepth);
 328                         (noffset >= 0) && (ndepth > 0);
 329                         noffset = fdt_next_node(info->fit, noffset, &ndepth)) {
 330                 if (ndepth == 1 && noffset != node) {
 331                         ret = rsa_verify_with_keynode(info, hash, sig, sig_len,
 332                                                       noffset);
 333                         if (!ret)
 334                                 break;
 335                 }
 336         }
 337
 338         return ret;
 339 }