path: root/drivers/char/hw_random/fips_drbg.c

/*
 * Copyright (c) 2014, The Linux Foundation. All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 and
 * only version 2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/device.h>
#include <linux/platform_device.h>
#include <linux/hw_random.h>
#include <linux/clk.h>
#include <linux/slab.h>
#include <linux/io.h>
#include <linux/err.h>
#include <linux/types.h>
#include <linux/msm-bus.h>
#include <linux/qrng.h>
#include <linux/fs.h>
#include <linux/cdev.h>

#include <linux/errno.h>
#include <linux/crypto.h>
#include <linux/scatterlist.h>
#include <linux/dma-mapping.h>
#include <linux/gfp.h>
#include <linux/string.h>

#include "msm_rng.h"
#include "fips_drbg.h"

/* The fips-140 random number generator is a wrapper around the CTR_DRBG
 * random number generator, which is built according to the
 * specifications in NIST SP 800-90 using AES-128.
 *
 * This wrapper has the following functionality
 * a. Entropy collection is via a callback.
 * b. A failure of CTR_DRBG because reseeding is needed invisibly
 *    causes the underlying CTR_DRBG instance to be reseeded with
 *    new random data and then the generate request is retried.
 * c. Limitations in CTR_DRBG (like not allowed more than 65536 bytes
 *    to be genrated in one request) are worked around.  At this level
 *    it just works.
 * d. On success the return value is zero.  If the callback was invoked
 *    and returned a non-zero value, that value is returned.  On all other
 *    errors -1 is returned.
 */

#ifndef NULL
  #define NULL  0
#endif

/*  32 bytes = 256 bits = seed length */
#define MAGIC 0xab10d161

#define RESEED_INTERVAL (1 << 31)

int get_entropy_callback(void *ctx, void *buf)
{
	struct msm_rng_device *msm_rng_dev = (struct msm_rng_device *)ctx;
	int ret_val = -1;

	if (NULL == ctx)
		return FIPS140_PRNG_ERR;

	if (NULL == buf)
		return FIPS140_PRNG_ERR;

	ret_val = msm_rng_direct_read(msm_rng_dev, buf);
	if ((size_t)ret_val != Q_HW_DRBG_BLOCK_BYTES)
		return ret_val;

	return 0;
}

/* Initialize *ctx. Automatically reseed after reseed_interval calls
 * to fips_drbg_gen.  The underlying CTR_DRBG will automatically be
 * reseeded every reseed_interval requests.  Values over
 * CTR_DRBG_MAX_RESEED_INTERVAL (2^48) or that are zero are silently
 * converted to CTR_DRBG_MAX_RESEED_INTERVAL.  (It is easy to justify
 * lowering values that are too large to CTR_DRBG_MAX_RESEED_INTERVAL
 * (the NIST SP800-90 limit): just silently enforcing the rules.
 * Silently converted 0 to to CTR_DRBG_MAX_RESEED_INTERVAL is harder.
 * The alternative is to return an error.  But since
 * CTR_DRBG_MAX_RESEED is safe, we relieve the caller of one more
 * error to worry about.)
 */
static int
do_fips_drbg_init(struct fips_drbg_ctx_s *ctx,
	      get_entropy_callback_t callback,
	      void *callback_ctx,
	      unsigned long long reseed_interval)
{
	uint8_t entropy_pool[Q_HW_DRBG_BLOCK_BYTES];
	enum ctr_drbg_status_t init_rv;
	int rv = -1;

	if (ctx == NULL)
		return FIPS140_PRNG_ERR;
	if (callback == NULL)
		return FIPS140_PRNG_ERR;
	if (reseed_interval == 0 ||
		reseed_interval > CTR_DRBG_MAX_RESEED_INTERVAL)
		reseed_interval = CTR_DRBG_MAX_RESEED_INTERVAL;

	/* fill in callback related fields in ctx */
	ctx->get_entropy_callback = callback;
	ctx->get_entropy_callback_ctx = callback_ctx;

	if (!ctx->fips_drbg_started) {
		rv = (*ctx->get_entropy_callback)(ctx->get_entropy_callback_ctx,
			ctx->prev_hw_drbg_block
			);
		if (rv != 0)
			return FIPS140_PRNG_ERR;
		ctx->fips_drbg_started = 1;
	}

	rv = (*ctx->get_entropy_callback)(ctx->get_entropy_callback_ctx,
		entropy_pool
		);
	if (rv != 0) {
		memset(entropy_pool, 0, Q_HW_DRBG_BLOCK_BYTES);
		return FIPS140_PRNG_ERR;
	}

	if (!memcmp(entropy_pool,
			ctx->prev_hw_drbg_block,
			Q_HW_DRBG_BLOCK_BYTES)) {
		memset(entropy_pool, 0, Q_HW_DRBG_BLOCK_BYTES);
		return FIPS140_PRNG_ERR;
	} else
		memcpy(ctx->prev_hw_drbg_block,
			entropy_pool,
			Q_HW_DRBG_BLOCK_BYTES);


	init_rv = ctr_drbg_instantiate(&ctx->ctr_drbg_ctx,
		entropy_pool,
		8 * MSM_ENTROPY_BUFFER_SIZE,
		entropy_pool + MSM_ENTROPY_BUFFER_SIZE,
		8 * 8,
		reseed_interval);

	memset(entropy_pool, 0, Q_HW_DRBG_BLOCK_BYTES);

	if (init_rv == 0)
		ctx->magic = MAGIC;

	return 0;
}

int fips_drbg_init(struct msm_rng_device *msm_rng_ctx)
{
	uint32_t ret_val = 0;

	ret_val = do_fips_drbg_init(msm_rng_ctx->drbg_ctx,
			get_entropy_callback,
			msm_rng_ctx,
			RESEED_INTERVAL
			);
	if (ret_val != 0)
		ret_val = FIPS140_PRNG_ERR;

	return ret_val;
}

/* Push new entropy into the CTR_DRBG instance in ctx, combining
 * it with the entropy already there.  On success, 0 is returned.  If
 * the callback returns a non-zero value, that value is returned.
 * Other errors return -1.
 */
static int
fips_drbg_reseed(struct fips_drbg_ctx_s *ctx)
{
	uint8_t entropy_pool[Q_HW_DRBG_BLOCK_BYTES];
	int rv;
	enum ctr_drbg_status_t init_rv;

	if (ctx == NULL)
		return FIPS140_PRNG_ERR;

	if (!ctx->fips_drbg_started) {
		rv = (*ctx->get_entropy_callback)(ctx->get_entropy_callback_ctx,
			ctx->prev_hw_drbg_block
			);
		if (rv != 0)
			return FIPS140_PRNG_ERR;
		ctx->fips_drbg_started = 1;
	}

	rv = (*ctx->get_entropy_callback)(ctx->get_entropy_callback_ctx,
		entropy_pool
		);
	if (rv != 0) {
		memset(entropy_pool, 0, Q_HW_DRBG_BLOCK_BYTES);
		return FIPS140_PRNG_ERR;
	}

	if (!memcmp(entropy_pool,
		    ctx->prev_hw_drbg_block,
		    Q_HW_DRBG_BLOCK_BYTES)) {
		memset(entropy_pool, 0, Q_HW_DRBG_BLOCK_BYTES);
		return FIPS140_PRNG_ERR;
	} else
		memcpy(ctx->prev_hw_drbg_block,
		       entropy_pool,
		       Q_HW_DRBG_BLOCK_BYTES);

	init_rv = ctr_drbg_reseed(&ctx->ctr_drbg_ctx,
				  entropy_pool,
				  8 * MSM_ENTROPY_BUFFER_SIZE);

	/* Zeroize the buffer for security. */
	memset(entropy_pool, 0, Q_HW_DRBG_BLOCK_BYTES);

	return (init_rv == CTR_DRBG_SUCCESS ?
				FIPS140_PRNG_OK :
				FIPS140_PRNG_ERR);
}

/* generate random bytes.  len is in bytes On success returns 0.  If
 * the callback returns a non-zero value, that is returned.  Other
 * errors return -1. */
int
fips_drbg_gen(struct fips_drbg_ctx_s *ctx, void *tgt, size_t len)
{

	/* The contorted flow in this function is so that the CTR_DRBG
	stuff can follow NIST SP 800-90, which has the generate function
	fail and return a special code if a reseed is needed. We also work
	around the CTR_DRBG limitation of the maximum request sized being
	2^19 bits. */

	enum ctr_drbg_status_t gen_rv;
	int rv;

	if (ctx == NULL || ctx->magic != MAGIC)
		return FIPS140_PRNG_ERR;
	if (tgt == NULL && len > 0)
		return FIPS140_PRNG_ERR;
	while (len > 0) {
		size_t req_len;

		if (len < (CTR_DRBG_MAX_REQ_LEN_BITS / 8))
			req_len = len;
		else
			req_len = CTR_DRBG_MAX_REQ_LEN_BITS / 8;

		gen_rv = ctr_drbg_generate(&ctx->ctr_drbg_ctx,
					   tgt,
					   8*req_len);
		switch (gen_rv) {
		case CTR_DRBG_SUCCESS:
			tgt = (uint8_t *)tgt + req_len;
			len -= req_len;
			break;
		case CTR_DRBG_NEEDS_RESEED:
			rv = fips_drbg_reseed(ctx);
			if (rv != 0)
				return rv;
			break;
		default:
			return FIPS140_PRNG_ERR;
		}
	}

	return 0;
}

/* free resources and zeroize state */
void
fips_drbg_final(struct fips_drbg_ctx_s *ctx)
{
	ctr_drbg_uninstantiate(&ctx->ctr_drbg_ctx);
	ctx->get_entropy_callback     = 0;
	ctx->get_entropy_callback_ctx = 0;
	ctx->fips_drbg_started        = 0;
	memset(ctx->prev_hw_drbg_block, 0, Q_HW_DRBG_BLOCK_BYTES);
	ctx->magic = 0;
}