random: introduce the initialization seed

Add random entropy with the module parameter as the initialization
seed when the kernel startup.

For guest OS working in VM, the random entropy will be less,
it cause the random module to initialize very slowly, and if
the application which running in guest os gets a certain amount of
random numbers in the initialization phase, it will be blocked.

This patch allows the VMM to provide a certain amount of random seed
when starting guest OS, speeding up the initialization of the entire
guest OS random module.

Before optimization:
[   22.180236] random: crng init done

After optimization:
[    1.553362] random: crng init done
Signed-off-by: NXingjun Liu <xingjun.lxj@alibaba-inc.com>
Reviewed-by: NLiu Jiang <gerry@linux.alibaba.com>
Reviewed-by: NCaspar Zhang <caspar@linux.alibaba.com>
Reviewed-by: Jia Zhang <zhang.jia@linux.alibaba.com>
Reviewed-by: NYang Shi <yang.shi@linux.alibaba.com>
Reviewed-by: NLiu Bo <bo.liu@linux.alibaba.com>

drivers/char/random.c

@@ -287,6 +287,7 @@
 #define OUTPUT_POOL_WORDS	(1 << (OUTPUT_POOL_SHIFT-5))
 #define SEC_XFER_SIZE		512
 #define EXTRACT_SIZE		10
+#define INIT_SEED_MAX_SIZE	32
 
 
 #define LONGS(x) (((x) + sizeof(unsigned long) - 1)/sizeof(unsigned long))
@@ -445,9 +446,13 @@ static struct ratelimit_state urandom_warning =
 	RATELIMIT_STATE_INIT("warn_urandom_randomness", HZ, 3);
 
 static int ratelimit_disable __read_mostly;
+static char *init_seed = "";
+static bool seed_inited;
 
 module_param_named(ratelimit_disable, ratelimit_disable, int, 0644);
 MODULE_PARM_DESC(ratelimit_disable, "Disable random ratelimit suppression");
+module_param(init_seed, charp, 0400);
+MODULE_PARM_DESC(init_seed, "Initialization random seed");
 
 /**********************************************************************
  *
@@ -1194,6 +1199,36 @@ void add_input_randomness(unsigned int type, unsigned int code,
 }
 EXPORT_SYMBOL_GPL(add_input_randomness);
 
+static void add_init_randomness(const char *buffer, size_t count)
+{
+	struct entropy_store *poolp = &input_pool;
+
+	mix_pool_bytes(poolp, buffer, count);
+	credit_entropy_bits(poolp, count * 8);
+}
+
+static size_t ascii_hex2bin(const char *buffer, size_t count,
+			    char *bin_buf, size_t len)
+{
+	const char *pbuf = buffer;
+	size_t bin_cnt;
+	char buf[4];
+	int i;
+
+	if (count == 0)
+		return 0;
+
+	bin_cnt = min(len, count / 2);
+	buf[2] = buf[3] = 0;
+	for (i = 0; i < bin_cnt; i++) {
+		buf[0] = *pbuf++;
+		buf[1] = *pbuf++;
+		if (kstrtou8(buf, 16, &bin_buf[i]) != 0)
+			return 0;
+	}
+	return bin_cnt;
+}
+
 static DEFINE_PER_CPU(struct fast_pool, irq_randomness);
 
 #ifdef ADD_INTERRUPT_BENCH
@@ -1243,6 +1278,8 @@ void add_interrupt_randomness(int irq, int irq_flags)
 	__u64			ip;
 	unsigned long		seed;
 	int			credit = 0;
+	size_t			seedlen;
+	char			seed_bin[INIT_SEED_MAX_SIZE];
 
 	if (cycles == 0)
 		cycles = get_reg(fast_pool, regs);
@@ -1272,6 +1309,15 @@ void add_interrupt_randomness(int irq, int irq_flags)
 	    !time_after(now, fast_pool->last + HZ))
 		return;
 
+	if (!seed_inited) {
+		seed_inited = 1;
+		seedlen = strlen(init_seed);
+		seedlen = ascii_hex2bin(init_seed, seedlen,
+					seed_bin, sizeof(seed_bin));
+		if (seedlen != 0)
+			add_init_randomness(seed_bin, seedlen);
+	}
+
 	r = &input_pool;
 	if (!spin_trylock(&r->lock))
 		return;