u-boot/lib/rsa/rsa-verify.c
Simon Glass 5426716231 rsa: Fix two errors in the implementation
1. Failure to set the return code correctly
2. Failure to detect the loop end condition when the value is equal to
the modulus.

Reported-by: Jeroen Hofstee <jeroen@myspectrum.nl>
Signed-off-by: Simon Glass <sjg@chromium.org>
2014-08-09 11:17:04 -04:00

422 lines
11 KiB
C

/*
* Copyright (c) 2013, Google Inc.
*
* SPDX-License-Identifier: GPL-2.0+
*/
#ifndef USE_HOSTCC
#include <common.h>
#include <fdtdec.h>
#include <asm/types.h>
#include <asm/byteorder.h>
#include <asm/errno.h>
#include <asm/types.h>
#include <asm/unaligned.h>
#else
#include "fdt_host.h"
#include "mkimage.h"
#include <fdt_support.h>
#endif
#include <u-boot/rsa.h>
#include <u-boot/sha1.h>
#include <u-boot/sha256.h>
#define UINT64_MULT32(v, multby) (((uint64_t)(v)) * ((uint32_t)(multby)))
#define get_unaligned_be32(a) fdt32_to_cpu(*(uint32_t *)a)
#define put_unaligned_be32(a, b) (*(uint32_t *)(b) = cpu_to_fdt32(a))
/* Default public exponent for backward compatibility */
#define RSA_DEFAULT_PUBEXP 65537
/**
* subtract_modulus() - subtract modulus from the given value
*
* @key: Key containing modulus to subtract
* @num: Number to subtract modulus from, as little endian word array
*/
static void subtract_modulus(const struct rsa_public_key *key, uint32_t num[])
{
int64_t acc = 0;
uint i;
for (i = 0; i < key->len; i++) {
acc += (uint64_t)num[i] - key->modulus[i];
num[i] = (uint32_t)acc;
acc >>= 32;
}
}
/**
* greater_equal_modulus() - check if a value is >= modulus
*
* @key: Key containing modulus to check
* @num: Number to check against modulus, as little endian word array
* @return 0 if num < modulus, 1 if num >= modulus
*/
static int greater_equal_modulus(const struct rsa_public_key *key,
uint32_t num[])
{
int i;
for (i = (int)key->len - 1; i >= 0; i--) {
if (num[i] < key->modulus[i])
return 0;
if (num[i] > key->modulus[i])
return 1;
}
return 1; /* equal */
}
/**
* montgomery_mul_add_step() - Perform montgomery multiply-add step
*
* Operation: montgomery result[] += a * b[] / n0inv % modulus
*
* @key: RSA key
* @result: Place to put result, as little endian word array
* @a: Multiplier
* @b: Multiplicand, as little endian word array
*/
static void montgomery_mul_add_step(const struct rsa_public_key *key,
uint32_t result[], const uint32_t a, const uint32_t b[])
{
uint64_t acc_a, acc_b;
uint32_t d0;
uint i;
acc_a = (uint64_t)a * b[0] + result[0];
d0 = (uint32_t)acc_a * key->n0inv;
acc_b = (uint64_t)d0 * key->modulus[0] + (uint32_t)acc_a;
for (i = 1; i < key->len; i++) {
acc_a = (acc_a >> 32) + (uint64_t)a * b[i] + result[i];
acc_b = (acc_b >> 32) + (uint64_t)d0 * key->modulus[i] +
(uint32_t)acc_a;
result[i - 1] = (uint32_t)acc_b;
}
acc_a = (acc_a >> 32) + (acc_b >> 32);
result[i - 1] = (uint32_t)acc_a;
if (acc_a >> 32)
subtract_modulus(key, result);
}
/**
* montgomery_mul() - Perform montgomery mutitply
*
* Operation: montgomery result[] = a[] * b[] / n0inv % modulus
*
* @key: RSA key
* @result: Place to put result, as little endian word array
* @a: Multiplier, as little endian word array
* @b: Multiplicand, as little endian word array
*/
static void montgomery_mul(const struct rsa_public_key *key,
uint32_t result[], uint32_t a[], const uint32_t b[])
{
uint i;
for (i = 0; i < key->len; ++i)
result[i] = 0;
for (i = 0; i < key->len; ++i)
montgomery_mul_add_step(key, result, a[i], b);
}
/**
* num_pub_exponent_bits() - Number of bits in the public exponent
*
* @key: RSA key
* @num_bits: Storage for the number of public exponent bits
*/
static int num_public_exponent_bits(const struct rsa_public_key *key,
int *num_bits)
{
uint64_t exponent;
int exponent_bits;
const uint max_bits = (sizeof(exponent) * 8);
exponent = key->exponent;
exponent_bits = 0;
if (!exponent) {
*num_bits = exponent_bits;
return 0;
}
for (exponent_bits = 1; exponent_bits < max_bits + 1; ++exponent_bits)
if (!(exponent >>= 1)) {
*num_bits = exponent_bits;
return 0;
}
return -EINVAL;
}
/**
* is_public_exponent_bit_set() - Check if a bit in the public exponent is set
*
* @key: RSA key
* @pos: The bit position to check
*/
static int is_public_exponent_bit_set(const struct rsa_public_key *key,
int pos)
{
return key->exponent & (1ULL << pos);
}
/**
* pow_mod() - in-place public exponentiation
*
* @key: RSA key
* @inout: Big-endian word array containing value and result
*/
static int pow_mod(const struct rsa_public_key *key, uint32_t *inout)
{
uint32_t *result, *ptr;
uint i;
int j, k;
/* Sanity check for stack size - key->len is in 32-bit words */
if (key->len > RSA_MAX_KEY_BITS / 32) {
debug("RSA key words %u exceeds maximum %d\n", key->len,
RSA_MAX_KEY_BITS / 32);
return -EINVAL;
}
uint32_t val[key->len], acc[key->len], tmp[key->len];
uint32_t a_scaled[key->len];
result = tmp; /* Re-use location. */
/* Convert from big endian byte array to little endian word array. */
for (i = 0, ptr = inout + key->len - 1; i < key->len; i++, ptr--)
val[i] = get_unaligned_be32(ptr);
if (0 != num_public_exponent_bits(key, &k))
return -EINVAL;
if (k < 2) {
debug("Public exponent is too short (%d bits, minimum 2)\n",
k);
return -EINVAL;
}
if (!is_public_exponent_bit_set(key, 0)) {
debug("LSB of RSA public exponent must be set.\n");
return -EINVAL;
}
/* the bit at e[k-1] is 1 by definition, so start with: C := M */
montgomery_mul(key, acc, val, key->rr); /* acc = a * RR / R mod n */
/* retain scaled version for intermediate use */
memcpy(a_scaled, acc, key->len * sizeof(a_scaled[0]));
for (j = k - 2; j > 0; --j) {
montgomery_mul(key, tmp, acc, acc); /* tmp = acc^2 / R mod n */
if (is_public_exponent_bit_set(key, j)) {
/* acc = tmp * val / R mod n */
montgomery_mul(key, acc, tmp, a_scaled);
} else {
/* e[j] == 0, copy tmp back to acc for next operation */
memcpy(acc, tmp, key->len * sizeof(acc[0]));
}
}
/* the bit at e[0] is always 1 */
montgomery_mul(key, tmp, acc, acc); /* tmp = acc^2 / R mod n */
montgomery_mul(key, acc, tmp, val); /* acc = tmp * a / R mod M */
memcpy(result, acc, key->len * sizeof(result[0]));
/* Make sure result < mod; result is at most 1x mod too large. */
if (greater_equal_modulus(key, result))
subtract_modulus(key, result);
/* Convert to bigendian byte array */
for (i = key->len - 1, ptr = inout; (int)i >= 0; i--, ptr++)
put_unaligned_be32(result[i], ptr);
return 0;
}
static int rsa_verify_key(const struct rsa_public_key *key, const uint8_t *sig,
const uint32_t sig_len, const uint8_t *hash,
struct checksum_algo *algo)
{
const uint8_t *padding;
int pad_len;
int ret;
if (!key || !sig || !hash || !algo)
return -EIO;
if (sig_len != (key->len * sizeof(uint32_t))) {
debug("Signature is of incorrect length %d\n", sig_len);
return -EINVAL;
}
debug("Checksum algorithm: %s", algo->name);
/* Sanity check for stack size */
if (sig_len > RSA_MAX_SIG_BITS / 8) {
debug("Signature length %u exceeds maximum %d\n", sig_len,
RSA_MAX_SIG_BITS / 8);
return -EINVAL;
}
uint32_t buf[sig_len / sizeof(uint32_t)];
memcpy(buf, sig, sig_len);
ret = pow_mod(key, buf);
if (ret)
return ret;
padding = algo->rsa_padding;
pad_len = algo->pad_len - algo->checksum_len;
/* Check pkcs1.5 padding bytes. */
if (memcmp(buf, padding, pad_len)) {
debug("In RSAVerify(): Padding check failed!\n");
return -EINVAL;
}
/* Check hash. */
if (memcmp((uint8_t *)buf + pad_len, hash, sig_len - pad_len)) {
debug("In RSAVerify(): Hash check failed!\n");
return -EACCES;
}
return 0;
}
static void rsa_convert_big_endian(uint32_t *dst, const uint32_t *src, int len)
{
int i;
for (i = 0; i < len; i++)
dst[i] = fdt32_to_cpu(src[len - 1 - i]);
}
static int rsa_verify_with_keynode(struct image_sign_info *info,
const void *hash, uint8_t *sig, uint sig_len, int node)
{
const void *blob = info->fdt_blob;
struct rsa_public_key key;
const void *modulus, *rr;
const uint64_t *public_exponent;
int length;
int ret;
if (node < 0) {
debug("%s: Skipping invalid node", __func__);
return -EBADF;
}
if (!fdt_getprop(blob, node, "rsa,n0-inverse", NULL)) {
debug("%s: Missing rsa,n0-inverse", __func__);
return -EFAULT;
}
key.len = fdtdec_get_int(blob, node, "rsa,num-bits", 0);
key.n0inv = fdtdec_get_int(blob, node, "rsa,n0-inverse", 0);
public_exponent = fdt_getprop(blob, node, "rsa,exponent", &length);
if (!public_exponent || length < sizeof(*public_exponent))
key.exponent = RSA_DEFAULT_PUBEXP;
else
key.exponent = fdt64_to_cpu(*public_exponent);
modulus = fdt_getprop(blob, node, "rsa,modulus", NULL);
rr = fdt_getprop(blob, node, "rsa,r-squared", NULL);
if (!key.len || !modulus || !rr) {
debug("%s: Missing RSA key info", __func__);
return -EFAULT;
}
/* Sanity check for stack size */
if (key.len > RSA_MAX_KEY_BITS || key.len < RSA_MIN_KEY_BITS) {
debug("RSA key bits %u outside allowed range %d..%d\n",
key.len, RSA_MIN_KEY_BITS, RSA_MAX_KEY_BITS);
return -EFAULT;
}
key.len /= sizeof(uint32_t) * 8;
uint32_t key1[key.len], key2[key.len];
key.modulus = key1;
key.rr = key2;
rsa_convert_big_endian(key.modulus, modulus, key.len);
rsa_convert_big_endian(key.rr, rr, key.len);
if (!key.modulus || !key.rr) {
debug("%s: Out of memory", __func__);
return -ENOMEM;
}
debug("key length %d\n", key.len);
ret = rsa_verify_key(&key, sig, sig_len, hash, info->algo->checksum);
if (ret) {
printf("%s: RSA failed to verify: %d\n", __func__, ret);
return ret;
}
return 0;
}
int rsa_verify(struct image_sign_info *info,
const struct image_region region[], int region_count,
uint8_t *sig, uint sig_len)
{
const void *blob = info->fdt_blob;
/* Reserve memory for maximum checksum-length */
uint8_t hash[info->algo->checksum->pad_len];
int ndepth, noffset;
int sig_node, node;
char name[100];
int ret;
/*
* Verify that the checksum-length does not exceed the
* rsa-signature-length
*/
if (info->algo->checksum->checksum_len >
info->algo->checksum->pad_len) {
debug("%s: invlaid checksum-algorithm %s for %s\n",
__func__, info->algo->checksum->name, info->algo->name);
return -EINVAL;
}
sig_node = fdt_subnode_offset(blob, 0, FIT_SIG_NODENAME);
if (sig_node < 0) {
debug("%s: No signature node found\n", __func__);
return -ENOENT;
}
/* Calculate checksum with checksum-algorithm */
info->algo->checksum->calculate(region, region_count, hash);
/* See if we must use a particular key */
if (info->required_keynode != -1) {
ret = rsa_verify_with_keynode(info, hash, sig, sig_len,
info->required_keynode);
if (!ret)
return ret;
}
/* Look for a key that matches our hint */
snprintf(name, sizeof(name), "key-%s", info->keyname);
node = fdt_subnode_offset(blob, sig_node, name);
ret = rsa_verify_with_keynode(info, hash, sig, sig_len, node);
if (!ret)
return ret;
/* No luck, so try each of the keys in turn */
for (ndepth = 0, noffset = fdt_next_node(info->fit, sig_node, &ndepth);
(noffset >= 0) && (ndepth > 0);
noffset = fdt_next_node(info->fit, noffset, &ndepth)) {
if (ndepth == 1 && noffset != node) {
ret = rsa_verify_with_keynode(info, hash, sig, sig_len,
noffset);
if (!ret)
break;
}
}
return ret;
}