// SPDX-License-Identifier: GPL-2.0-or-later
/*
* PRNG: Pseudo Random Number Generator
* Based on NIST Recommended PRNG From ANSI X9.31 Appendix A.2.4 using
* AES 128 cipher
*
* (C) Neil Horman <[email protected]>
*/
#include <crypto/internal/cipher.h>
#include <crypto/internal/rng.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/string.h>
#define DEFAULT_PRNG_KEY "0123456789abcdef"
#define DEFAULT_PRNG_KSZ 16
#define DEFAULT_BLK_SZ 16
#define DEFAULT_V_SEED "zaybxcwdveuftgsh"
/*
* Flags for the prng_context flags field
*/
#define PRNG_FIXED_SIZE 0x1
#define PRNG_NEED_RESET 0x2
/*
* Note: DT is our counter value
* I is our intermediate value
* V is our seed vector
* See http://csrc.nist.gov/groups/STM/cavp/documents/rng/931rngext.pdf
* for implementation details
*/
struct prng_context {
spinlock_t prng_lock;
unsigned char rand_data[DEFAULT_BLK_SZ];
unsigned char last_rand_data[DEFAULT_BLK_SZ];
unsigned char DT[DEFAULT_BLK_SZ];
unsigned char I[DEFAULT_BLK_SZ];
unsigned char V[DEFAULT_BLK_SZ];
u32 rand_data_valid;
struct crypto_cipher *tfm;
u32 flags;
};
static int dbg;
static void hexdump(char *note, unsigned char *buf, unsigned int len)
{
if (dbg) {
printk(KERN_CRIT "%s", note);
print_hex_dump(KERN_CONT, "", DUMP_PREFIX_OFFSET,
16, 1,
buf, len, false);
}
}
#define dbgprint(format, args...) do {\
if (dbg)\
printk(format, ##args);\
} while (0)
static void xor_vectors(unsigned char *in1, unsigned char *in2,
unsigned char *out, unsigned int size)
{
int i;
for (i = 0; i < size; i++)
out[i] = in1[i] ^ in2[i];
}
/*
* Returns DEFAULT_BLK_SZ bytes of random data per call
* returns 0 if generation succeeded, <0 if something went wrong
*/
static int _get_more_prng_bytes(struct prng_context *ctx, int cont_test)
{
int i;
unsigned char tmp[DEFAULT_BLK_SZ];
unsigned char *output = NULL;
dbgprint(KERN_CRIT "Calling _get_more_prng_bytes for context %p\n",
ctx);
hexdump("Input DT: ", ctx->DT, DEFAULT_BLK_SZ);
hexdump("Input I: ", ctx->I, DEFAULT_BLK_SZ);
hexdump("Input V: ", ctx->V, DEFAULT_BLK_SZ);
/*
* This algorithm is a 3 stage state machine
*/
for (i = 0; i < 3; i++) {
switch (i) {
case 0:
/*
* Start by encrypting the counter value
* This gives us an intermediate value I
*/
memcpy(tmp, ctx->DT, DEFAULT_BLK_SZ);
output = ctx->I;
hexdump("tmp stage 0: ", tmp, DEFAULT_BLK_SZ);
break;
case 1:
/*
* Next xor I with our secret vector V
* encrypt that result to obtain our
* pseudo random data which we output
*/
xor_vectors(ctx->I, ctx->V, tmp, DEFAULT_BLK_SZ);
hexdump("tmp stage 1: ", tmp, DEFAULT_BLK_SZ);
output = ctx->rand_data;
break;
case 2:
/*
* First check that we didn't produce the same
* random data that we did last time around through this
*/
if (!memcmp(ctx->rand_data, ctx->last_rand_data,
DEFAULT_BLK_SZ)) {
if (cont_test) {
panic("cprng %p Failed repetition check!\n",
ctx);
}
printk(KERN_ERR
"ctx %p Failed repetition check!\n",
ctx);
ctx->flags |= PRNG_NEED_RESET;
return -EINVAL;
}
memcpy(ctx->last_rand_data, ctx->rand_data,
DEFAULT_BLK_SZ);
/*
* Lastly xor the random data with I
* and encrypt that to obtain a new secret vector V
*/
xor_vectors(ctx->rand_data, ctx->I, tmp,
DEFAULT_BLK_SZ);
output = ctx->V;
hexdump("tmp stage 2: ", tmp, DEFAULT_BLK_SZ);
break;
}
/* do the encryption */
crypto_cipher_encrypt_one(ctx->tfm, output, tmp);
}
/*
* Now update our DT value
*/
for (i = DEFAULT_BLK_SZ - 1; i >= 0; i--) {
ctx->DT[i] += 1;
if (ctx->DT[i] != 0)
break;
}
dbgprint("Returning new block for context %p\n", ctx);
ctx->rand_data_valid = 0;
hexdump("Output DT: ", ctx->DT, DEFAULT_BLK_SZ);
hexdump("Output I: ", ctx->I, DEFAULT_BLK_SZ);
hexdump("Output V: ", ctx->V, DEFAULT_BLK_SZ);
hexdump("New Random Data: ", ctx->rand_data, DEFAULT_BLK_SZ);
return 0;
}
/* Our exported functions */
static int get_prng_bytes(char *buf, size_t nbytes, struct prng_context *ctx,
int do_cont_test)
{
unsigned char *ptr = buf;
unsigned int byte_count = (unsigned int)nbytes;
int err;
spin_lock_bh(&ctx->prng_lock);
err = -EINVAL;
if (ctx->flags & PRNG_NEED_RESET)
goto done;
/*
* If the FIXED_SIZE flag is on, only return whole blocks of
* pseudo random data
*/
err = -EINVAL;
if (ctx->flags & PRNG_FIXED_SIZE) {
if (nbytes < DEFAULT_BLK_SZ)
goto done;
byte_count = DEFAULT_BLK_SZ;
}
/*
* Return 0 in case of success as mandated by the kernel
* crypto API interface definition.
*/
err = 0;
dbgprint(KERN_CRIT "getting %d random bytes for context %p\n",
byte_count, ctx);
remainder:
if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
if (_get_more_prng_bytes(ctx, do_cont_test) < 0) {
memset(buf, 0, nbytes);
err = -EINVAL;
goto done;
}
}
/*
* Copy any data less than an entire block
*/
if (byte_count < DEFAULT_BLK_SZ) {
empty_rbuf:
while (ctx->rand_data_valid < DEFAULT_BLK_SZ) {
*ptr = ctx->rand_data[ctx->rand_data_valid];
ptr++;
byte_count--;
ctx->rand_data_valid++;
if (byte_count == 0)
goto done;
}
}
/*
* Now copy whole blocks
*/
for (; byte_count >= DEFAULT_BLK_SZ; byte_count -= DEFAULT_BLK_SZ) {
if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
if (_get_more_prng_bytes(ctx, do_cont_test) < 0) {
memset(buf, 0, nbytes);
err = -EINVAL;
goto done;
}
}
if (ctx->rand_data_valid > 0)
goto empty_rbuf;
memcpy(ptr, ctx->rand_data, DEFAULT_BLK_SZ);
ctx->rand_data_valid += DEFAULT_BLK_SZ;
ptr += DEFAULT_BLK_SZ;
}
/*
* Now go back and get any remaining partial block
*/
if (byte_count)
goto remainder;
done:
spin_unlock_bh(&ctx->prng_lock);
dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n",
err, ctx);
return err;
}
static void free_prng_context(struct prng_context *ctx)
{
crypto_free_cipher(ctx->tfm);
}
static int reset_prng_context(struct prng_context *ctx,
const unsigned char *key, size_t klen,
const unsigned char *V, const unsigned char *DT)
{
int ret;
const unsigned char *prng_key;
spin_lock_bh(&ctx->prng_lock);
ctx->flags |= PRNG_NEED_RESET;
prng_key = (key != NULL) ? key : (unsigned char *)DEFAULT_PRNG_KEY;
if (!key)
klen = DEFAULT_PRNG_KSZ;
if (V)
memcpy(ctx->V, V, DEFAULT_BLK_SZ);
else
memcpy(ctx->V, DEFAULT_V_SEED, DEFAULT_BLK_SZ);
if (DT)
memcpy(ctx->DT, DT, DEFAULT_BLK_SZ);
else
memset(ctx->DT, 0, DEFAULT_BLK_SZ);
memset(ctx->rand_data, 0, DEFAULT_BLK_SZ);
memset(ctx->last_rand_data, 0, DEFAULT_BLK_SZ);
ctx->rand_data_valid = DEFAULT_BLK_SZ;
ret = crypto_cipher_setkey(ctx->tfm, prng_key, klen);
if (ret) {
dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n",
crypto_cipher_get_flags(ctx->tfm));
goto out;
}
ret = 0;
ctx->flags &= ~PRNG_NEED_RESET;
out:
spin_unlock_bh(&ctx->prng_lock);
return ret;
}
static int cprng_init(struct crypto_tfm *tfm)
{
struct prng_context *ctx = crypto_tfm_ctx(tfm);
spin_lock_init(&ctx->prng_lock);
ctx->tfm = crypto_alloc_cipher("aes", 0, 0);
if (IS_ERR(ctx->tfm)) {
dbgprint(KERN_CRIT "Failed to alloc tfm for context %p\n",
ctx);
return PTR_ERR(ctx->tfm);
}
if (reset_prng_context(ctx, NULL, DEFAULT_PRNG_KSZ, NULL, NULL) < 0)
return -EINVAL;
/*
* after allocation, we should always force the user to reset
* so they don't inadvertently use the insecure default values
* without specifying them intentially
*/
ctx->flags |= PRNG_NEED_RESET;
return 0;
}
static void cprng_exit(struct crypto_tfm *tfm)
{
free_prng_context(crypto_tfm_ctx(tfm));
}
static int cprng_get_random(struct crypto_rng *tfm,
const u8 *src, unsigned int slen,
u8 *rdata, unsigned int dlen)
{
struct prng_context *prng = crypto_rng_ctx(tfm);
return get_prng_bytes(rdata, dlen, prng, 0);
}
/*
* This is the cprng_registered reset method the seed value is
* interpreted as the tuple { V KEY DT}
* V and KEY are required during reset, and DT is optional, detected
* as being present by testing the length of the seed
*/
static int cprng_reset(struct crypto_rng *tfm,
const u8 *seed, unsigned int slen)
{
struct prng_context *prng = crypto_rng_ctx(tfm);
const u8 *key = seed + DEFAULT_BLK_SZ;
const u8 *dt = NULL;
if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
return -EINVAL;
if (slen >= (2 * DEFAULT_BLK_SZ + DEFAULT_PRNG_KSZ))
dt = key + DEFAULT_PRNG_KSZ;
reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, dt);
if (prng->flags & PRNG_NEED_RESET)
return -EINVAL;
return 0;
}
#ifdef CONFIG_CRYPTO_FIPS
static int fips_cprng_get_random(struct crypto_rng *tfm,
const u8 *src, unsigned int slen,
u8 *rdata, unsigned int dlen)
{
struct prng_context *prng = crypto_rng_ctx(tfm);
return get_prng_bytes(rdata, dlen, prng, 1);
}
static int fips_cprng_reset(struct crypto_rng *tfm,
const u8 *seed, unsigned int slen)
{
u8 rdata[DEFAULT_BLK_SZ];
const u8 *key = seed + DEFAULT_BLK_SZ;
int rc;
struct prng_context *prng = crypto_rng_ctx(tfm);
if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
return -EINVAL;
/* fips strictly requires seed != key */
if (!memcmp(seed, key, DEFAULT_PRNG_KSZ))
return -EINVAL;
rc = cprng_reset(tfm, seed, slen);
if (!rc)
goto out;
/* this primes our continuity test */
rc = get_prng_bytes(rdata, DEFAULT_BLK_SZ, prng, 0);
prng->rand_data_valid = DEFAULT_BLK_SZ;
out:
return rc;
}
#endif
static struct rng_alg rng_algs[] = { {
.generate = cprng_get_random,
.seed = cprng_reset,
.seedsize = DEFAULT_PRNG_KSZ + 2 * DEFAULT_BLK_SZ,
.base = {
.cra_name = "stdrng",
.cra_driver_name = "ansi_cprng",
.cra_priority = 100,
.cra_ctxsize = sizeof(struct prng_context),
.cra_module = THIS_MODULE,
.cra_init = cprng_init,
.cra_exit = cprng_exit,
}
#ifdef CONFIG_CRYPTO_FIPS
}, {
.generate = fips_cprng_get_random,
.seed = fips_cprng_reset,
.seedsize = DEFAULT_PRNG_KSZ + 2 * DEFAULT_BLK_SZ,
.base = {
.cra_name = "fips(ansi_cprng)",
.cra_driver_name = "fips_ansi_cprng",
.cra_priority = 300,
.cra_ctxsize = sizeof(struct prng_context),
.cra_module = THIS_MODULE,
.cra_init = cprng_init,
.cra_exit = cprng_exit,
}
#endif
} };
/* Module initalization */
static int __init prng_mod_init(void)
{
return crypto_register_rngs(rng_algs, ARRAY_SIZE(rng_algs));
}
static void __exit prng_mod_fini(void)
{
crypto_unregister_rngs(rng_algs, ARRAY_SIZE(rng_algs));
}
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
MODULE_AUTHOR("Neil Horman <[email protected]>");
module_param(dbg, int, 0);
MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
subsys_initcall(prng_mod_init);
module_exit(prng_mod_fini);
MODULE_ALIAS_CRYPTO("stdrng");
MODULE_ALIAS_CRYPTO("ansi_cprng");
MODULE_IMPORT_NS(CRYPTO_INTERNAL);
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