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Commit 81731551 authored by Jason A. Donenfeld's avatar Jason A. Donenfeld Committed by Greg Kroah-Hartman
Browse files

random: get rid of secondary crngs 



commit a9412d510ab9a9ba411fea612903631d2e1f1601 upstream.

As the comment said, this is indeed a "hack". Since it was introduced,
it's been a constant state machine nightmare, with lots of subtle early
boot issues and a wildly complex set of machinery to keep everything in
sync. Rather than continuing to play whack-a-mole with this approach,
this commit simply removes it entirely. This commit is preparation for
"random: use simpler fast key erasure flow on per-cpu keys" in this
series, which introduces a simpler (and faster) mechanism to accomplish
the same thing.

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>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent c15fc80b

drivers/char/random.c

+53 −172
Original line number Diff line number Diff line
@@ -323,14 +323,11 @@ static struct crng_state primary_crng = { 
 * its value (from 0->1->2).

 */

static int crng_init = 0;

static bool crng_need_final_init = false;

#define crng_ready() (likely(crng_init > 1))

static int crng_init_cnt = 0;

static unsigned long crng_global_init_time = 0;

#define CRNG_INIT_CNT_THRESH (2 * CHACHA_KEY_SIZE)

static void _extract_crng(struct crng_state *crng, u8 out[CHACHA_BLOCK_SIZE]);

static void _crng_backtrack_protect(struct crng_state *crng,

				    u8 tmp[CHACHA_BLOCK_SIZE], int used);

static void extract_crng(u8 out[CHACHA_BLOCK_SIZE]);

static void crng_backtrack_protect(u8 tmp[CHACHA_BLOCK_SIZE], int used);

static void process_random_ready_list(void);

static void _get_random_bytes(void *buf, int nbytes);
@@ -365,7 +362,7 @@ static struct { 


static void extract_entropy(void *buf, size_t nbytes);



static void crng_reseed(struct crng_state *crng);

static void crng_reseed(void);



/*

 * This function adds bytes into the entropy "pool".  It does not
@@ -464,7 +461,7 @@ static void credit_entropy_bits(int nbits) 
	trace_credit_entropy_bits(nbits, entropy_count, _RET_IP_);



	if (crng_init < 2 && entropy_count >= POOL_MIN_BITS)

		crng_reseed(&primary_crng);

		crng_reseed();

}



/*********************************************************************
@@ -477,16 +474,7 @@ static void credit_entropy_bits(int nbits) 


static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait);



/*

 * Hack to deal with crazy userspace progams when they are all trying

 * to access /dev/urandom in parallel.  The programs are almost

 * certainly doing something terribly wrong, but we'll work around

 * their brain damage.

 */

static struct crng_state **crng_node_pool __read_mostly;



static void invalidate_batched_entropy(void);

static void numa_crng_init(void);



static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);

static int __init parse_trust_cpu(char *arg)
@@ -495,24 +483,6 @@ static int __init parse_trust_cpu(char *arg) 
}

early_param("random.trust_cpu", parse_trust_cpu);



static bool crng_init_try_arch(struct crng_state *crng)

{

	int i;

	bool arch_init = true;

	unsigned long rv;



	for (i = 4; i < 16; i++) {

		if (!arch_get_random_seed_long(&rv) &&

		    !arch_get_random_long(&rv)) {

			rv = random_get_entropy();

			arch_init = false;

		}

		crng->state[i] ^= rv;

	}



	return arch_init;

}



static bool __init crng_init_try_arch_early(void)

{

	int i;
@@ -531,100 +501,17 @@ static bool __init crng_init_try_arch_early(void) 
	return arch_init;

}



static void crng_initialize_secondary(struct crng_state *crng)

{

	chacha_init_consts(crng->state);

	_get_random_bytes(&crng->state[4], sizeof(u32) * 12);

	crng_init_try_arch(crng);

	crng->init_time = jiffies - CRNG_RESEED_INTERVAL - 1;

}



static void __init crng_initialize_primary(void)

static void __init crng_initialize(void)

{

	extract_entropy(&primary_crng.state[4], sizeof(u32) * 12);

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

		invalidate_batched_entropy();

		numa_crng_init();

		crng_init = 2;

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

	}

	primary_crng.init_time = jiffies - CRNG_RESEED_INTERVAL - 1;

}



static void crng_finalize_init(void)

{

	if (!system_wq) {

		/* We can't call numa_crng_init until we have workqueues,

		 * so mark this for processing later. */

		crng_need_final_init = true;

		return;

	}



	invalidate_batched_entropy();

	numa_crng_init();

	crng_init = 2;

	crng_need_final_init = false;

	process_random_ready_list();

	wake_up_interruptible(&crng_init_wait);

	kill_fasync(&fasync, SIGIO, POLL_IN);

	pr_notice("crng init done\n");

	if (unseeded_warning.missed) {

		pr_notice("%d get_random_xx warning(s) missed due to ratelimiting\n",

			  unseeded_warning.missed);

		unseeded_warning.missed = 0;

	}

	if (urandom_warning.missed) {

		pr_notice("%d urandom warning(s) missed due to ratelimiting\n",

			  urandom_warning.missed);

		urandom_warning.missed = 0;

	}

}



static void do_numa_crng_init(struct work_struct *work)

{

	int i;

	struct crng_state *crng;

	struct crng_state **pool;



	pool = kcalloc(nr_node_ids, sizeof(*pool), GFP_KERNEL | __GFP_NOFAIL);

	for_each_online_node(i) {

		crng = kmalloc_node(sizeof(struct crng_state),

				    GFP_KERNEL | __GFP_NOFAIL, i);

		spin_lock_init(&crng->lock);

		crng_initialize_secondary(crng);

		pool[i] = crng;

	}

	/* pairs with READ_ONCE() in select_crng() */

	if (cmpxchg_release(&crng_node_pool, NULL, pool) != NULL) {

		for_each_node(i)

			kfree(pool[i]);

		kfree(pool);

	}

}



static DECLARE_WORK(numa_crng_init_work, do_numa_crng_init);



static void numa_crng_init(void)

{

	if (IS_ENABLED(CONFIG_NUMA))

		schedule_work(&numa_crng_init_work);

}



static struct crng_state *select_crng(void)

{

	if (IS_ENABLED(CONFIG_NUMA)) {

		struct crng_state **pool;

		int nid = numa_node_id();



		/* pairs with cmpxchg_release() in do_numa_crng_init() */

		pool = READ_ONCE(crng_node_pool);

		if (pool && pool[nid])

			return pool[nid];

	}



	return &primary_crng;

}



/*

 * 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
@@ -702,17 +589,15 @@ static int crng_slow_load(const u8 *cp, size_t len) 
	return 1;

}



static void crng_reseed(struct crng_state *crng)

static void crng_reseed(void)

{

	unsigned long flags;

	int i;

	int i, entropy_count;

	union {

		u8 block[CHACHA_BLOCK_SIZE];

		u32 key[8];

	} buf;



	if (crng == &primary_crng) {

		int entropy_count;

	do {

		entropy_count = READ_ONCE(input_pool.entropy_count);

		if (entropy_count < POOL_MIN_BITS)
@@ -721,49 +606,54 @@ static void crng_reseed(struct crng_state *crng) 
	extract_entropy(buf.key, sizeof(buf.key));

	wake_up_interruptible(&random_write_wait);

	kill_fasync(&fasync, SIGIO, POLL_OUT);

	} else {

		_extract_crng(&primary_crng, buf.block);

		_crng_backtrack_protect(&primary_crng, buf.block,

					CHACHA_KEY_SIZE);

	}

	spin_lock_irqsave(&crng->lock, flags);



	spin_lock_irqsave(&primary_crng.lock, flags);

	for (i = 0; i < 8; i++)

		crng->state[i + 4] ^= buf.key[i];

		primary_crng.state[i + 4] ^= buf.key[i];

	memzero_explicit(&buf, sizeof(buf));

	WRITE_ONCE(crng->init_time, jiffies);

	spin_unlock_irqrestore(&crng->lock, flags);

	if (crng == &primary_crng && crng_init < 2)

		crng_finalize_init();

	WRITE_ONCE(primary_crng.init_time, jiffies);

	spin_unlock_irqrestore(&primary_crng.lock, flags);

	if (crng_init < 2) {

		invalidate_batched_entropy();

		crng_init = 2;

		process_random_ready_list();

		wake_up_interruptible(&crng_init_wait);

		kill_fasync(&fasync, SIGIO, POLL_IN);

		pr_notice("crng init done\n");

		if (unseeded_warning.missed) {

			pr_notice("%d get_random_xx warning(s) missed due to ratelimiting\n",

				  unseeded_warning.missed);

			unseeded_warning.missed = 0;

		}

		if (urandom_warning.missed) {

			pr_notice("%d urandom warning(s) missed due to ratelimiting\n",

				  urandom_warning.missed);

			urandom_warning.missed = 0;

		}



static void _extract_crng(struct crng_state *crng, u8 out[CHACHA_BLOCK_SIZE])

{

	unsigned long flags, init_time;



	if (crng_ready()) {

		init_time = READ_ONCE(crng->init_time);

		if (time_after(READ_ONCE(crng_global_init_time), init_time) ||

		    time_after(jiffies, init_time + CRNG_RESEED_INTERVAL))

			crng_reseed(crng);

	}

	spin_lock_irqsave(&crng->lock, flags);

	chacha20_block(&crng->state[0], out);

	if (crng->state[12] == 0)

		crng->state[13]++;

	spin_unlock_irqrestore(&crng->lock, flags);

}



static void extract_crng(u8 out[CHACHA_BLOCK_SIZE])

{

	_extract_crng(select_crng(), out);

	unsigned long flags, init_time;



	if (crng_ready()) {

		init_time = READ_ONCE(primary_crng.init_time);

		if (time_after(jiffies, init_time + CRNG_RESEED_INTERVAL))

			crng_reseed();

	}

	spin_lock_irqsave(&primary_crng.lock, flags);

	chacha20_block(&primary_crng.state[0], out);

	if (primary_crng.state[12] == 0)

		primary_crng.state[13]++;

	spin_unlock_irqrestore(&primary_crng.lock, flags);

}



/*

 * 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[CHACHA_BLOCK_SIZE], int used)

static void crng_backtrack_protect(u8 tmp[CHACHA_BLOCK_SIZE], int used)

{

	unsigned long flags;

	u32 *s, *d;
@@ -774,17 +664,12 @@ static void _crng_backtrack_protect(struct crng_state *crng, 
		extract_crng(tmp);

		used = 0;

	}

	spin_lock_irqsave(&crng->lock, flags);

	spin_lock_irqsave(&primary_crng.lock, flags);

	s = (u32 *)&tmp[used];

	d = &crng->state[4];

	d = &primary_crng.state[4];

	for (i = 0; i < 8; i++)

		*d++ ^= *s++;

	spin_unlock_irqrestore(&crng->lock, flags);

}



static void crng_backtrack_protect(u8 tmp[CHACHA_BLOCK_SIZE], int used)

{

	_crng_backtrack_protect(select_crng(), tmp, used);

	spin_unlock_irqrestore(&primary_crng.lock, flags);

}



static ssize_t extract_crng_user(void __user *buf, size_t nbytes)
@@ -1371,10 +1256,7 @@ static void __init init_std_data(void) 
int __init rand_initialize(void)

{

	init_std_data();

	if (crng_need_final_init)

		crng_finalize_init();

	crng_initialize_primary();

	crng_global_init_time = jiffies;

	crng_initialize();

	if (ratelimit_disable) {

		urandom_warning.interval = 0;

		unseeded_warning.interval = 0;
@@ -1544,8 +1426,7 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg) 
			return -EPERM;

		if (crng_init < 2)

			return -ENODATA;

		crng_reseed(&primary_crng);

		WRITE_ONCE(crng_global_init_time, jiffies - 1);

		crng_reseed();

		return 0;

	default:

		return -EINVAL;