linux kernel 随机数

Linux kernel 生成随机数

仅以此做一个学习记录。

随机数

随机数kernel 里面有提供一个专门的file：

drivers/char/random.c

API:

/*
 * This function is the exported kernel interface.  It returns some
 * number of good random numbers, suitable for key generation, seeding
 * TCP sequence numbers, etc.  It does not rely on the hardware random
 * number generator.  For random bytes direct from the hardware RNG
 * (when available), use get_random_bytes_arch(). In order to ensure
 * that the randomness provided by this function is okay, the function
 * wait_for_random_bytes() should be called and return 0 at least once
 * at any point prior.
 */
static void _get_random_bytes(void *buf, int nbytes)
{
	__u8 tmp[CHACHA_BLOCK_SIZE] __aligned(4);

	trace_get_random_bytes(nbytes, _RET_IP_);

	while (nbytes >= CHACHA_BLOCK_SIZE) {
		extract_crng(buf);
		buf += CHACHA_BLOCK_SIZE;
		nbytes -= CHACHA_BLOCK_SIZE;
	}

	if (nbytes > 0) {
		extract_crng(tmp);
		memcpy(buf, tmp, nbytes);
		crng_backtrack_protect(tmp, nbytes);
	} else
		crng_backtrack_protect(tmp, CHACHA_BLOCK_SIZE);
	memzero_explicit(tmp, sizeof(tmp));
}

void get_random_bytes(void *buf, int nbytes)
{
	static void *previous;

	warn_unseeded_randomness(&previous);
	_get_random_bytes(buf, nbytes);
}
EXPORT_SYMBOL(get_random_bytes);

/*
 * Wait for the urandom pool to be seeded and thus guaranteed to supply
 * cryptographically secure random numbers. This applies to: the /dev/urandom
 * device, the get_random_bytes function, and the get_random_{u32,u64,int,long}
 * family of functions. Using any of these functions without first calling
 * this function forfeits the guarantee of security.
 *
 * Returns: 0 if the urandom pool has been seeded.
 *          -ERESTARTSYS if the function was interrupted by a signal.
 */
int wait_for_random_bytes(void)
{
	if (likely(crng_ready()))
		return 0;
	return wait_event_interruptible(crng_init_wait, crng_ready());
}
EXPORT_SYMBOL(wait_for_random_bytes);

https://elixir.bootlin.com/linux/latest/source/drivers/char/random.c#L1646