random: add backtracking protection to the CRNG (c92e040d) · Commits · e / devices / android_kernel_xiaomi_nabu

drivers/char/random.c

+49 −5

Original line number	Diff line number	Diff line
		@@ -438,7 +438,8 @@ static int crng_init_cnt = 0;
		#define CRNG_INIT_CNT_THRESH (2*CHACHA20_KEY_SIZE)
		static void _extract_crng(struct crng_state *crng,
		__u8 out[CHACHA20_BLOCK_SIZE]);
		static void extract_crng(__u8 out[CHACHA20_BLOCK_SIZE]);
		static void _crng_backtrack_protect(struct crng_state *crng,
		__u8 tmp[CHACHA20_BLOCK_SIZE], int used);
		static void process_random_ready_list(void);

		/**********************************************************************
		@@ -826,8 +827,11 @@ static void crng_reseed(struct crng_state crng, struct entropy_store r)
		num = extract_entropy(r, &buf, 32, 16, 0);
		if (num == 0)
		return;
		} else
		} else {
		_extract_crng(&primary_crng, buf.block);
		_crng_backtrack_protect(&primary_crng, buf.block,
		CHACHA20_KEY_SIZE);
		}
		spin_lock_irqsave(&primary_crng.lock, flags);
		for (i = 0; i < 8; i++) {
		unsigned long rv;
		@@ -889,9 +893,46 @@ static void extract_crng(__u8 out[CHACHA20_BLOCK_SIZE])
		_extract_crng(crng, out);
		}

		/*
		* Use the leftover bytes from the CRNG block output (if there is
		* enough) to mutate the CRNG key to provide backtracking protection.
		*/
		static void _crng_backtrack_protect(struct crng_state *crng,
		__u8 tmp[CHACHA20_BLOCK_SIZE], int used)
		{
		unsigned long flags;
		__u32 s, d;
		int i;

		used = round_up(used, sizeof(__u32));
		if (used + CHACHA20_KEY_SIZE > CHACHA20_BLOCK_SIZE) {
		extract_crng(tmp);
		used = 0;
		}
		spin_lock_irqsave(&crng->lock, flags);
		s = (__u32 *) &tmp[used];
		d = &crng->state[4];
		for (i=0; i < 8; i++)
		d++ ^= s++;
		spin_unlock_irqrestore(&crng->lock, flags);
		}

		static void crng_backtrack_protect(__u8 tmp[CHACHA20_BLOCK_SIZE], int used)
		{
		struct crng_state *crng = NULL;

		#ifdef CONFIG_NUMA
		if (crng_node_pool)
		crng = crng_node_pool[numa_node_id()];
		if (crng == NULL)
		#endif
		crng = &primary_crng;
		_crng_backtrack_protect(crng, tmp, used);
		}

		static ssize_t extract_crng_user(void __user *buf, size_t nbytes)
		{
		ssize_t ret = 0, i;
		ssize_t ret = 0, i = CHACHA20_BLOCK_SIZE;
		__u8 tmp[CHACHA20_BLOCK_SIZE];
		int large_request = (nbytes > 256);

		@@ -916,6 +957,7 @@ static ssize_t extract_crng_user(void __user *buf, size_t nbytes)
		buf += i;
		ret += i;
		}
		crng_backtrack_protect(tmp, i);

		/* Wipe data just written to memory */
		memzero_explicit(tmp, sizeof(tmp));
		@@ -1473,8 +1515,10 @@ void get_random_bytes(void *buf, int nbytes)
		if (nbytes > 0) {
		extract_crng(tmp);
		memcpy(buf, tmp, nbytes);
		memzero_explicit(tmp, nbytes);
		}
		crng_backtrack_protect(tmp, nbytes);
		} else
		crng_backtrack_protect(tmp, CHACHA20_BLOCK_SIZE);
		memzero_explicit(tmp, sizeof(tmp));
		}
		EXPORT_SYMBOL(get_random_bytes);