Commit 0791e8b6 authored by Jason A. Donenfeld's avatar Jason A. Donenfeld
Browse files

random: tie batched entropy generation to base_crng generation 



Now that we have an explicit base_crng generation counter, we don't need
a separate one for batched entropy. Rather, we can just move the
generation forward every time we change crng_init state or update the
base_crng key.

Cc: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: default avatarEric Biggers <ebiggers@google.com>
Reviewed-by: default avatarDominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: default avatarJason A. Donenfeld <Jason@zx2c4.com>
parent 7191c628

drivers/char/random.c

+8 −21
Original line number Diff line number Diff line
@@ -430,8 +430,6 @@ static DEFINE_PER_CPU(struct crng, crngs) = { 


static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait);



static void invalidate_batched_entropy(void);



/*

 * crng_fast_load() can be called by code in the interrupt service

 * path.  So we can't afford to dilly-dally. Returns the number of
@@ -454,7 +452,7 @@ static size_t crng_fast_load(const void *cp, size_t len) 
		src++; crng_init_cnt++; len--; ret++;

	}

	if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) {

		invalidate_batched_entropy();

		++base_crng.generation;

		crng_init = 1;

	}

	spin_unlock_irqrestore(&base_crng.lock, flags);
@@ -531,7 +529,6 @@ static void crng_reseed(void) 
	WRITE_ONCE(base_crng.generation, next_gen);

	WRITE_ONCE(base_crng.birth, jiffies);

	if (crng_init < 2) {

		invalidate_batched_entropy();

		crng_init = 2;

		finalize_init = true;

	}
@@ -1256,8 +1253,9 @@ int __init rand_initialize(void) 
	mix_pool_bytes(utsname(), sizeof(*(utsname())));



	extract_entropy(base_crng.key, sizeof(base_crng.key));

	++base_crng.generation;



	if (arch_init && trust_cpu && crng_init < 2) {

		invalidate_batched_entropy();

		crng_init = 2;

		pr_notice("crng init done (trusting CPU's manufacturer)\n");

	}
@@ -1607,8 +1605,6 @@ static int __init random_sysctls_init(void) 
device_initcall(random_sysctls_init);

#endif	/* CONFIG_SYSCTL */



static atomic_t batch_generation = ATOMIC_INIT(0);



struct batched_entropy {

	union {

		/*
@@ -1622,8 +1618,8 @@ struct batched_entropy { 
		u32 entropy_u32[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(u32))];

	};

	local_lock_t lock;

	unsigned long generation;

	unsigned int position;

	int generation;

};



/*
@@ -1643,14 +1639,14 @@ u64 get_random_u64(void) 
	unsigned long flags;

	struct batched_entropy *batch;

	static void *previous;

	int next_gen;

	unsigned long next_gen;



	warn_unseeded_randomness(&previous);



	local_lock_irqsave(&batched_entropy_u64.lock, flags);

	batch = raw_cpu_ptr(&batched_entropy_u64);



	next_gen = atomic_read(&batch_generation);

	next_gen = READ_ONCE(base_crng.generation);

	if (batch->position >= ARRAY_SIZE(batch->entropy_u64) ||

	    next_gen != batch->generation) {

		_get_random_bytes(batch->entropy_u64, sizeof(batch->entropy_u64));
@@ -1677,14 +1673,14 @@ u32 get_random_u32(void) 
	unsigned long flags;

	struct batched_entropy *batch;

	static void *previous;

	int next_gen;

	unsigned long next_gen;



	warn_unseeded_randomness(&previous);



	local_lock_irqsave(&batched_entropy_u32.lock, flags);

	batch = raw_cpu_ptr(&batched_entropy_u32);



	next_gen = atomic_read(&batch_generation);

	next_gen = READ_ONCE(base_crng.generation);

	if (batch->position >= ARRAY_SIZE(batch->entropy_u32) ||

	    next_gen != batch->generation) {

		_get_random_bytes(batch->entropy_u32, sizeof(batch->entropy_u32));
@@ -1700,15 +1696,6 @@ u32 get_random_u32(void) 
}

EXPORT_SYMBOL(get_random_u32);



/* It's important to invalidate all potential batched entropy that might

 * be stored before the crng is initialized, which we can do lazily by

 * bumping the generation counter.

 */

static void invalidate_batched_entropy(void)

{

	atomic_inc(&batch_generation);

}



/**

 * randomize_page - Generate a random, page aligned address

 * @start:	The smallest acceptable address the caller will take.