random32: make prandom_u32() output unpredictable (c51f8f88) · Commits · 戴 / test

drivers/char/random.c

+0 −1

Original line number	Diff line number	Diff line
		@@ -1277,7 +1277,6 @@ void add_interrupt_randomness(int irq, int irq_flags)

		fast_mix(fast_pool);
		add_interrupt_bench(cycles);
		this_cpu_add(net_rand_state.s1, fast_pool->pool[cycles & 3]);

		if (unlikely(crng_init == 0)) {
		if ((fast_pool->count >= 64) &&

include/linux/prandom.h

+34 −2

Original line number	Diff line number	Diff line
		@@ -16,12 +16,44 @@ void prandom_bytes(void *buf, size_t nbytes);
		void prandom_seed(u32 seed);
		void prandom_reseed_late(void);

		#if BITS_PER_LONG == 64
		/*
		* The core SipHash round function. Each line can be executed in
		* parallel given enough CPU resources.
		*/
		#define PRND_SIPROUND(v0, v1, v2, v3) ( \
		v0 += v1, v1 = rol64(v1, 13), v2 += v3, v3 = rol64(v3, 16), \
		v1 ^= v0, v0 = rol64(v0, 32), v3 ^= v2, \
		v0 += v3, v3 = rol64(v3, 21), v2 += v1, v1 = rol64(v1, 17), \
		v3 ^= v0, v1 ^= v2, v2 = rol64(v2, 32) \
		)

		#define PRND_K0 (0x736f6d6570736575 ^ 0x6c7967656e657261)
		#define PRND_K1 (0x646f72616e646f6d ^ 0x7465646279746573)

		#elif BITS_PER_LONG == 32
		/*
		* On 32-bit machines, we use HSipHash, a reduced-width version of SipHash.
		* This is weaker, but 32-bit machines are not used for high-traffic
		* applications, so there is less output for an attacker to analyze.
		*/
		#define PRND_SIPROUND(v0, v1, v2, v3) ( \
		v0 += v1, v1 = rol32(v1, 5), v2 += v3, v3 = rol32(v3, 8), \
		v1 ^= v0, v0 = rol32(v0, 16), v3 ^= v2, \
		v0 += v3, v3 = rol32(v3, 7), v2 += v1, v1 = rol32(v1, 13), \
		v3 ^= v0, v1 ^= v2, v2 = rol32(v2, 16) \
		)
		#define PRND_K0 0x6c796765
		#define PRND_K1 0x74656462

		#else
		#error Unsupported BITS_PER_LONG
		#endif

		struct rnd_state {
		__u32 s1, s2, s3, s4;
		};

		DECLARE_PER_CPU(struct rnd_state, net_rand_state);

		u32 prandom_u32_state(struct rnd_state *state);
		void prandom_bytes_state(struct rnd_state state, void buf, size_t nbytes);
		void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state);

kernel/time/timer.c

+0 −7

Original line number	Diff line number	Diff line
		@@ -1717,13 +1717,6 @@ void update_process_times(int user_tick)
		scheduler_tick();
		if (IS_ENABLED(CONFIG_POSIX_TIMERS))
		run_posix_cpu_timers();

		/* The current CPU might make use of net randoms without receiving IRQs
		* to renew them often enough. Let's update the net_rand_state from a
		* non-constant value that's not affine to the number of calls to make
		* sure it's updated when there's some activity (we don't care in idle).
		*/
		this_cpu_add(net_rand_state.s1, rol32(jiffies, 24) + user_tick);
		}

		/**

lib/random32.c

+284 −180

Original line number	Diff line number	Diff line
		@@ -41,16 +41,6 @@
		#include <asm/unaligned.h>
		#include <trace/events/random.h>

		#ifdef CONFIG_RANDOM32_SELFTEST
		static void __init prandom_state_selftest(void);
		#else
		static inline void prandom_state_selftest(void)
		{
		}
		#endif

		DEFINE_PER_CPU(struct rnd_state, net_rand_state) __latent_entropy;

		/**
		* prandom_u32_state - seeded pseudo-random number generator.
		* @state: pointer to state structure holding seeded state.
		@@ -70,26 +60,6 @@ u32 prandom_u32_state(struct rnd_state *state)
		}
		EXPORT_SYMBOL(prandom_u32_state);

		/**
		* prandom_u32 - pseudo random number generator
		*
		* A 32 bit pseudo-random number is generated using a fast
		* algorithm suitable for simulation. This algorithm is NOT
		* considered safe for cryptographic use.
		*/
		u32 prandom_u32(void)
		{
		struct rnd_state *state = &get_cpu_var(net_rand_state);
		u32 res;

		res = prandom_u32_state(state);
		trace_prandom_u32(res);
		put_cpu_var(net_rand_state);

		return res;
		}
		EXPORT_SYMBOL(prandom_u32);

		/**
		* prandom_bytes_state - get the requested number of pseudo-random bytes
		*
		@@ -121,20 +91,6 @@ void prandom_bytes_state(struct rnd_state state, void buf, size_t bytes)
		}
		EXPORT_SYMBOL(prandom_bytes_state);

		/**
		* prandom_bytes - get the requested number of pseudo-random bytes
		* @buf: where to copy the pseudo-random bytes to
		* @bytes: the requested number of bytes
		*/
		void prandom_bytes(void *buf, size_t bytes)
		{
		struct rnd_state *state = &get_cpu_var(net_rand_state);

		prandom_bytes_state(state, buf, bytes);
		put_cpu_var(net_rand_state);
		}
		EXPORT_SYMBOL(prandom_bytes);

		static void prandom_warmup(struct rnd_state *state)
		{
		/* Calling RNG ten times to satisfy recurrence condition */
		@@ -150,96 +106,6 @@ static void prandom_warmup(struct rnd_state *state)
		prandom_u32_state(state);
		}

		static u32 __extract_hwseed(void)
		{
		unsigned int val = 0;

		(void)(arch_get_random_seed_int(&val) \|\|
		arch_get_random_int(&val));

		return val;
		}

		static void prandom_seed_early(struct rnd_state *state, u32 seed,
		bool mix_with_hwseed)
		{
		#define LCG(x) ((x) * 69069U) /* super-duper LCG */
		#define HWSEED() (mix_with_hwseed ? __extract_hwseed() : 0)
		state->s1 = __seed(HWSEED() ^ LCG(seed), 2U);
		state->s2 = __seed(HWSEED() ^ LCG(state->s1), 8U);
		state->s3 = __seed(HWSEED() ^ LCG(state->s2), 16U);
		state->s4 = __seed(HWSEED() ^ LCG(state->s3), 128U);
		}

		/**
		* prandom_seed - add entropy to pseudo random number generator
		* @entropy: entropy value
		*
		* Add some additional entropy to the prandom pool.
		*/
		void prandom_seed(u32 entropy)
		{
		int i;
		/*
		* No locking on the CPUs, but then somewhat random results are, well,
		* expected.
		*/
		for_each_possible_cpu(i) {
		struct rnd_state *state = &per_cpu(net_rand_state, i);

		state->s1 = __seed(state->s1 ^ entropy, 2U);
		prandom_warmup(state);
		}
		}
		EXPORT_SYMBOL(prandom_seed);

		/*
		* Generate some initially weak seeding values to allow
		* to start the prandom_u32() engine.
		*/
		static int __init prandom_init(void)
		{
		int i;

		prandom_state_selftest();

		for_each_possible_cpu(i) {
		struct rnd_state *state = &per_cpu(net_rand_state, i);
		u32 weak_seed = (i + jiffies) ^ random_get_entropy();

		prandom_seed_early(state, weak_seed, true);
		prandom_warmup(state);
		}

		return 0;
		}
		core_initcall(prandom_init);

		static void __prandom_timer(struct timer_list *unused);

		static DEFINE_TIMER(seed_timer, __prandom_timer);

		static void __prandom_timer(struct timer_list *unused)
		{
		u32 entropy;
		unsigned long expires;

		get_random_bytes(&entropy, sizeof(entropy));
		prandom_seed(entropy);

		/* reseed every ~60 seconds, in [40 .. 80) interval with slack */
		expires = 40 + prandom_u32_max(40);
		seed_timer.expires = jiffies + msecs_to_jiffies(expires * MSEC_PER_SEC);

		add_timer(&seed_timer);
		}

		static void __init __prandom_start_seed_timer(void)
		{
		seed_timer.expires = jiffies + msecs_to_jiffies(40 * MSEC_PER_SEC);
		add_timer(&seed_timer);
		}

		void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state)
		{
		int i;
		@@ -259,51 +125,6 @@ void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state)
		}
		EXPORT_SYMBOL(prandom_seed_full_state);

		/*
		* Generate better values after random number generator
		* is fully initialized.
		*/
		static void __prandom_reseed(bool late)
		{
		unsigned long flags;
		static bool latch = false;
		static DEFINE_SPINLOCK(lock);

		/* Asking for random bytes might result in bytes getting
		* moved into the nonblocking pool and thus marking it
		* as initialized. In this case we would double back into
		* this function and attempt to do a late reseed.
		* Ignore the pointless attempt to reseed again if we're
		* already waiting for bytes when the nonblocking pool
		* got initialized.
		*/

		/* only allow initial seeding (late == false) once */
		if (!spin_trylock_irqsave(&lock, flags))
		return;

		if (latch && !late)
		goto out;

		latch = true;
		prandom_seed_full_state(&net_rand_state);
		out:
		spin_unlock_irqrestore(&lock, flags);
		}

		void prandom_reseed_late(void)
		{
		__prandom_reseed(true);
		}

		static int __init prandom_reseed(void)
		{
		__prandom_reseed(false);
		__prandom_start_seed_timer();
		return 0;
		}
		late_initcall(prandom_reseed);

		#ifdef CONFIG_RANDOM32_SELFTEST
		static struct prandom_test1 {
		u32 seed;
		@@ -423,7 +244,28 @@ static struct prandom_test2 {
		{ 407983964U, 921U, 728767059U },
		};

		static void __init prandom_state_selftest(void)
		static u32 __extract_hwseed(void)
		{
		unsigned int val = 0;

		(void)(arch_get_random_seed_int(&val) \|\|
		arch_get_random_int(&val));

		return val;
		}

		static void prandom_seed_early(struct rnd_state *state, u32 seed,
		bool mix_with_hwseed)
		{
		#define LCG(x) ((x) * 69069U) /* super-duper LCG */
		#define HWSEED() (mix_with_hwseed ? __extract_hwseed() : 0)
		state->s1 = __seed(HWSEED() ^ LCG(seed), 2U);
		state->s2 = __seed(HWSEED() ^ LCG(state->s1), 8U);
		state->s3 = __seed(HWSEED() ^ LCG(state->s2), 16U);
		state->s4 = __seed(HWSEED() ^ LCG(state->s3), 128U);
		}

		static int __init prandom_state_selftest(void)
		{
		int i, j, errors = 0, runs = 0;
		bool error = false;
		@@ -463,5 +305,267 @@ static void __init prandom_state_selftest(void)
		pr_warn("prandom: %d/%d self tests failed\n", errors, runs);
		else
		pr_info("prandom: %d self tests passed\n", runs);
		return 0;
		}
		core_initcall(prandom_state_selftest);
		#endif

		/*
		* The prandom_u32() implementation is now completely separate from the
		* prandom_state() functions, which are retained (for now) for compatibility.
		*
		* Because of (ab)use in the networking code for choosing random TCP/UDP port
		* numbers, which open DoS possibilities if guessable, we want something
		* stronger than a standard PRNG. But the performance requirements of
		* the network code do not allow robust crypto for this application.
		*
		* So this is a homebrew Junior Spaceman implementation, based on the
		* lowest-latency trustworthy crypto primitive available, SipHash.
		* (The authors of SipHash have not been consulted about this abuse of
		* their work.)
		*
		* Standard SipHash-2-4 uses 2n+4 rounds to hash n words of input to
		* one word of output. This abbreviated version uses 2 rounds per word
		* of output.
		*/

		struct siprand_state {
		unsigned long v0;
		unsigned long v1;
		unsigned long v2;
		unsigned long v3;
		};

		static DEFINE_PER_CPU(struct siprand_state, net_rand_state) __latent_entropy;

		/*
		* This is the core CPRNG function. As "pseudorandom", this is not used
		* for truly valuable things, just intended to be a PITA to guess.
		* For maximum speed, we do just two SipHash rounds per word. This is
		* the same rate as 4 rounds per 64 bits that SipHash normally uses,
		* so hopefully it's reasonably secure.
		*
		* There are two changes from the official SipHash finalization:
		* - We omit some constants XORed with v2 in the SipHash spec as irrelevant;
		* they are there only to make the output rounds distinct from the input
		* rounds, and this application has no input rounds.
		* - Rather than returning v0^v1^v2^v3, return v1+v3.
		* If you look at the SipHash round, the last operation on v3 is
		* "v3 ^= v0", so "v0 ^ v3" just undoes that, a waste of time.
		* Likewise "v1 ^= v2". (The rotate of v2 makes a difference, but
		* it still cancels out half of the bits in v2 for no benefit.)
		* Second, since the last combining operation was xor, continue the
		* pattern of alternating xor/add for a tiny bit of extra non-linearity.
		*/
		static inline u32 siprand_u32(struct siprand_state *s)
		{
		unsigned long v0 = s->v0, v1 = s->v1, v2 = s->v2, v3 = s->v3;

		PRND_SIPROUND(v0, v1, v2, v3);
		PRND_SIPROUND(v0, v1, v2, v3);
		s->v0 = v0; s->v1 = v1; s->v2 = v2; s->v3 = v3;
		return v1 + v3;
		}


		/**
		* prandom_u32 - pseudo random number generator
		*
		* A 32 bit pseudo-random number is generated using a fast
		* algorithm suitable for simulation. This algorithm is NOT
		* considered safe for cryptographic use.
		*/
		u32 prandom_u32(void)
		{
		struct siprand_state *state = get_cpu_ptr(&net_rand_state);
		u32 res = siprand_u32(state);

		trace_prandom_u32(res);
		put_cpu_ptr(&net_rand_state);
		return res;
		}
		EXPORT_SYMBOL(prandom_u32);

		/**
		* prandom_bytes - get the requested number of pseudo-random bytes
		* @buf: where to copy the pseudo-random bytes to
		* @bytes: the requested number of bytes
		*/
		void prandom_bytes(void *buf, size_t bytes)
		{
		struct siprand_state *state = get_cpu_ptr(&net_rand_state);
		u8 *ptr = buf;

		while (bytes >= sizeof(u32)) {
		put_unaligned(siprand_u32(state), (u32 *)ptr);
		ptr += sizeof(u32);
		bytes -= sizeof(u32);
		}

		if (bytes > 0) {
		u32 rem = siprand_u32(state);

		do {
		*ptr++ = (u8)rem;
		rem >>= BITS_PER_BYTE;
		} while (--bytes > 0);
		}
		put_cpu_ptr(&net_rand_state);
		}
		EXPORT_SYMBOL(prandom_bytes);

		/**
		* prandom_seed - add entropy to pseudo random number generator
		* @entropy: entropy value
		*
		* Add some additional seed material to the prandom pool.
		* The "entropy" is actually our IP address (the only caller is
		* the network code), not for unpredictability, but to ensure that
		* different machines are initialized differently.
		*/
		void prandom_seed(u32 entropy)
		{
		int i;

		add_device_randomness(&entropy, sizeof(entropy));

		for_each_possible_cpu(i) {
		struct siprand_state *state = per_cpu_ptr(&net_rand_state, i);
		unsigned long v0 = state->v0, v1 = state->v1;
		unsigned long v2 = state->v2, v3 = state->v3;

		do {
		v3 ^= entropy;
		PRND_SIPROUND(v0, v1, v2, v3);
		PRND_SIPROUND(v0, v1, v2, v3);
		v0 ^= entropy;
		} while (unlikely(!v0 \|\| !v1 \|\| !v2 \|\| !v3));

		WRITE_ONCE(state->v0, v0);
		WRITE_ONCE(state->v1, v1);
		WRITE_ONCE(state->v2, v2);
		WRITE_ONCE(state->v3, v3);
		}
		}
		EXPORT_SYMBOL(prandom_seed);

		/*
		* Generate some initially weak seeding values to allow
		* the prandom_u32() engine to be started.
		*/
		static int __init prandom_init_early(void)
		{
		int i;
		unsigned long v0, v1, v2, v3;

		if (!arch_get_random_long(&v0))
		v0 = jiffies;
		if (!arch_get_random_long(&v1))
		v1 = random_get_entropy();
		v2 = v0 ^ PRND_K0;
		v3 = v1 ^ PRND_K1;

		for_each_possible_cpu(i) {
		struct siprand_state *state;

		v3 ^= i;
		PRND_SIPROUND(v0, v1, v2, v3);
		PRND_SIPROUND(v0, v1, v2, v3);
		v0 ^= i;

		state = per_cpu_ptr(&net_rand_state, i);
		state->v0 = v0; state->v1 = v1;
		state->v2 = v2; state->v3 = v3;
		}

		return 0;
		}
		core_initcall(prandom_init_early);


		/* Stronger reseeding when available, and periodically thereafter. */
		static void prandom_reseed(struct timer_list *unused);

		static DEFINE_TIMER(seed_timer, prandom_reseed);

		static void prandom_reseed(struct timer_list *unused)
		{
		unsigned long expires;
		int i;

		/*
		* Reinitialize each CPU's PRNG with 128 bits of key.
		* No locking on the CPUs, but then somewhat random results are,
		* well, expected.
		*/
		for_each_possible_cpu(i) {
		struct siprand_state *state;
		unsigned long v0 = get_random_long(), v2 = v0 ^ PRND_K0;
		unsigned long v1 = get_random_long(), v3 = v1 ^ PRND_K1;
		#if BITS_PER_LONG == 32
		int j;

		/*
		* On 32-bit machines, hash in two extra words to
		* approximate 128-bit key length. Not that the hash
		* has that much security, but this prevents a trivial
		* 64-bit brute force.
		*/
		for (j = 0; j < 2; j++) {
		unsigned long m = get_random_long();

		v3 ^= m;
		PRND_SIPROUND(v0, v1, v2, v3);
		PRND_SIPROUND(v0, v1, v2, v3);
		v0 ^= m;
		}
		#endif
		/*
		* Probably impossible in practice, but there is a
		* theoretical risk that a race between this reseeding
		* and the target CPU writing its state back could
		* create the all-zero SipHash fixed point.
		*
		* To ensure that never happens, ensure the state
		* we write contains no zero words.
		*/
		state = per_cpu_ptr(&net_rand_state, i);
		WRITE_ONCE(state->v0, v0 ? v0 : -1ul);
		WRITE_ONCE(state->v1, v1 ? v1 : -1ul);
		WRITE_ONCE(state->v2, v2 ? v2 : -1ul);
		WRITE_ONCE(state->v3, v3 ? v3 : -1ul);
		}

		/* reseed every ~60 seconds, in [40 .. 80) interval with slack */
		expires = round_jiffies(jiffies + 40 * HZ + prandom_u32_max(40 * HZ));
		mod_timer(&seed_timer, expires);
		}

		/*
		* The random ready callback can be called from almost any interrupt.
		* To avoid worrying about whether it's safe to delay that interrupt
		* long enough to seed all CPUs, just schedule an immediate timer event.
		*/
		static void prandom_timer_start(struct random_ready_callback *unused)
		{
		mod_timer(&seed_timer, jiffies);
		}

		/*
		* Start periodic full reseeding as soon as strong
		* random numbers are available.
		*/
		static int __init prandom_init_late(void)
		{
		static struct random_ready_callback random_ready = {
		.func = prandom_timer_start
		};
		int ret = add_random_ready_callback(&random_ready);

		if (ret == -EALREADY) {
		prandom_timer_start(&random_ready);
		ret = 0;
		}
		return ret;
		}
		late_initcall(prandom_init_late);

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