[PATCH 5.17 034/111] random: group entropy collection functions

Greg Kroah-Hartman
2022-05-27T09:02:32Z

commit 92c653cf14400946f376a29b828d6af7e01f38dd upstream.

This pulls all of the entropy collection-focused functions into the
fourth labeled section.

No functional changes.

Cc: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/char/random.c | 370 +++++++++++++++++++++++++++-----------------------
1 file changed, 206 insertions(+), 164 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1039,60 +1039,112 @@ static bool drain_entropy(void *buf, siz
return true;
}

-struct fast_pool {
- union {
- u32 pool32[4];
- u64 pool64[2];
- };
- unsigned long last;
- u16 reg_idx;
- u8 count;
-};
+
+/**********************************************************************
+ *
+ * Entropy collection routines.
+ *
+ * The following exported functions are used for pushing entropy into
+ * the above entropy accumulation routines:
+ *
+ * void add_device_randomness(const void *buf, size_t size);
+ * void add_input_randomness(unsigned int type, unsigned int code,
+ * unsigned int value);
+ * void add_disk_randomness(struct gendisk *disk);
+ * void add_hwgenerator_randomness(const void *buffer, size_t count,
+ * size_t entropy);
+ * void add_bootloader_randomness(const void *buf, size_t size);
+ * void add_interrupt_randomness(int irq);
+ *
+ * add_device_randomness() adds data to the input pool that
+ * is likely to differ between two devices (or possibly even per boot).
+ * This would be things like MAC addresses or serial numbers, or the
+ * read-out of the RTC. This does *not* credit any actual entropy to
+ * the pool, but it initializes the pool to different values for devices
+ * that might otherwise be identical and have very little entropy
+ * available to them (particularly common in the embedded world).
+ *
+ * add_input_randomness() uses the input layer interrupt timing, as well
+ * as the event type information from the hardware.
+ *
+ * add_disk_randomness() uses what amounts to the seek time of block
+ * layer request events, on a per-disk_devt basis, as input to the
+ * entropy pool. Note that high-speed solid state drives with very low
+ * seek times do not make for good sources of entropy, as their seek
+ * times are usually fairly consistent.
+ *
+ * The above two routines try to estimate how many bits of entropy
+ * to credit. They do this by keeping track of the first and second
+ * order deltas of the event timings.
+ *
+ * add_hwgenerator_randomness() is for true hardware RNGs, and will credit
+ * entropy as specified by the caller. If the entropy pool is full it will
+ * block until more entropy is needed.
+ *
+ * add_bootloader_randomness() is the same as add_hwgenerator_randomness() or
+ * add_device_randomness(), depending on whether or not the configuration
+ * option CONFIG_RANDOM_TRUST_BOOTLOADER is set.
+ *
+ * add_interrupt_randomness() uses the interrupt timing as random
+ * inputs to the entropy pool. Using the cycle counters and the irq source
+ * as inputs, it feeds the input pool roughly once a second or after 64
+ * interrupts, crediting 1 bit of entropy for whichever comes first.
+ *
+ **********************************************************************/
+
+static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);
+static int __init parse_trust_cpu(char *arg)
+{
+ return kstrtobool(arg, &trust_cpu);
+}
+early_param("random.trust_cpu", parse_trust_cpu);

/*
- * This is a fast mixing routine used by the interrupt randomness
- * collector. It's hardcoded for an 128 bit pool and assumes that any
- * locks that might be needed are taken by the caller.
+ * The first collection of entropy occurs at system boot while interrupts
+ * are still turned off. Here we push in RDSEED, a timestamp, and utsname().
+ * Depending on the above configuration knob, RDSEED may be considered
+ * sufficient for initialization. Note that much earlier setup may already
+ * have pushed entropy into the input pool by the time we get here.
*/
-static void fast_mix(u32 pool[4])
+int __init rand_initialize(void)
{
- u32 a = pool[0], b = pool[1];
- u32 c = pool[2], d = pool[3];
-
- a += b; c += d;
- b = rol32(b, 6); d = rol32(d, 27);
- d ^= a; b ^= c;
+ size_t i;
+ ktime_t now = ktime_get_real();
+ bool arch_init = true;
+ unsigned long rv;

- a += b; c += d;
- b = rol32(b, 16); d = rol32(d, 14);
- d ^= a; b ^= c;
+ for (i = 0; i < BLAKE2S_BLOCK_SIZE; i += sizeof(rv)) {
+ if (!arch_get_random_seed_long_early(&rv) &&
+ !arch_get_random_long_early(&rv)) {
+ rv = random_get_entropy();
+ arch_init = false;
+ }
+ mix_pool_bytes(&rv, sizeof(rv));
+ }
+ mix_pool_bytes(&now, sizeof(now));
+ mix_pool_bytes(utsname(), sizeof(*(utsname())));

- a += b; c += d;
- b = rol32(b, 6); d = rol32(d, 27);
- d ^= a; b ^= c;
+ extract_entropy(base_crng.key, sizeof(base_crng.key));
+ ++base_crng.generation;

- a += b; c += d;
- b = rol32(b, 16); d = rol32(d, 14);
- d ^= a; b ^= c;
+ if (arch_init && trust_cpu && crng_init < 2) {
+ crng_init = 2;
+ pr_notice("crng init done (trusting CPU's manufacturer)\n");
+ }

- pool[0] = a; pool[1] = b;
- pool[2] = c; pool[3] = d;
+ if (ratelimit_disable) {
+ urandom_warning.interval = 0;
+ unseeded_warning.interval = 0;
+ }
+ return 0;
}

-/*********************************************************************
- *
- * Entropy input management
- *
- *********************************************************************/
-
/* There is one of these per entropy source */
struct timer_rand_state {
cycles_t last_time;
long last_delta, last_delta2;
};

-#define INIT_TIMER_RAND_STATE { INITIAL_JIFFIES, };
-
/*
* Add device- or boot-specific data to the input pool to help
* initialize it.
@@ -1116,8 +1168,6 @@ void add_device_randomness(const void *b
}
EXPORT_SYMBOL(add_device_randomness);

-static struct timer_rand_state input_timer_state = INIT_TIMER_RAND_STATE;
-
/*
* This function adds entropy to the entropy "pool" by using timing
* delays. It uses the timer_rand_state structure to make an estimate
@@ -1179,8 +1229,9 @@ void add_input_randomness(unsigned int t
unsigned int value)
{
static unsigned char last_value;
+ static struct timer_rand_state input_timer_state = { INITIAL_JIFFIES };

- /* ignore autorepeat and the like */
+ /* Ignore autorepeat and the like. */
if (value == last_value)
return;

@@ -1190,6 +1241,119 @@ void add_input_randomness(unsigned int t
}
EXPORT_SYMBOL_GPL(add_input_randomness);

+#ifdef CONFIG_BLOCK
+void add_disk_randomness(struct gendisk *disk)
+{
+ if (!disk || !disk->random)
+ return;
+ /* First major is 1, so we get >= 0x200 here. */
+ add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
+}
+EXPORT_SYMBOL_GPL(add_disk_randomness);
+
+void rand_initialize_disk(struct gendisk *disk)
+{
+ struct timer_rand_state *state;
+
+ /*
+ * If kzalloc returns null, we just won't use that entropy
+ * source.
+ */
+ state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
+ if (state) {
+ state->last_time = INITIAL_JIFFIES;
+ disk->random = state;
+ }
+}
+#endif
+
+/*
+ * Interface for in-kernel drivers of true hardware RNGs.
+ * Those devices may produce endless random bits and will be throttled
+ * when our pool is full.
+ */
+void add_hwgenerator_randomness(const void *buffer, size_t count,
+ size_t entropy)
+{
+ if (unlikely(crng_init == 0)) {
+ size_t ret = crng_fast_load(buffer, count);
+ mix_pool_bytes(buffer, ret);
+ count -= ret;
+ buffer += ret;
+ if (!count || crng_init == 0)
+ return;
+ }
+
+ /*
+ * Throttle writing if we're above the trickle threshold.
+ * We'll be woken up again once below POOL_MIN_BITS, when
+ * the calling thread is about to terminate, or once
+ * CRNG_RESEED_INTERVAL has elapsed.
+ */
+ wait_event_interruptible_timeout(random_write_wait,
+ !system_wq || kthread_should_stop() ||
+ input_pool.entropy_count < POOL_MIN_BITS,
+ CRNG_RESEED_INTERVAL);
+ mix_pool_bytes(buffer, count);
+ credit_entropy_bits(entropy);
+}
+EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
+
+/*
+ * Handle random seed passed by bootloader.
+ * If the seed is trustworthy, it would be regarded as hardware RNGs. Otherwise
+ * it would be regarded as device data.
+ * The decision is controlled by CONFIG_RANDOM_TRUST_BOOTLOADER.
+ */
+void add_bootloader_randomness(const void *buf, size_t size)
+{
+ if (IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER))
+ add_hwgenerator_randomness(buf, size, size * 8);
+ else
+ add_device_randomness(buf, size);
+}
+EXPORT_SYMBOL_GPL(add_bootloader_randomness);
+
+struct fast_pool {
+ union {
+ u32 pool32[4];
+ u64 pool64[2];
+ };
+ unsigned long last;
+ u16 reg_idx;
+ u8 count;
+};
+
+/*
+ * This is a fast mixing routine used by the interrupt randomness
+ * collector. It's hardcoded for an 128 bit pool and assumes that any
+ * locks that might be needed are taken by the caller.
+ */
+static void fast_mix(u32 pool[4])
+{
+ u32 a = pool[0], b = pool[1];
+ u32 c = pool[2], d = pool[3];
+
+ a += b; c += d;
+ b = rol32(b, 6); d = rol32(d, 27);
+ d ^= a; b ^= c;
+
+ a += b; c += d;
+ b = rol32(b, 16); d = rol32(d, 14);
+ d ^= a; b ^= c;
+
+ a += b; c += d;
+ b = rol32(b, 6); d = rol32(d, 27);
+ d ^= a; b ^= c;
+
+ a += b; c += d;
+ b = rol32(b, 16); d = rol32(d, 14);
+ d ^= a; b ^= c;
+
+ pool[0] = a; pool[1] = b;
+ pool[2] = c; pool[3] = d;
+}
+
static DEFINE_PER_CPU(struct fast_pool, irq_randomness);

static u32 get_reg(struct fast_pool *f, struct pt_regs *regs)
@@ -1259,22 +1423,11 @@ void add_interrupt_randomness(int irq)

fast_pool->count = 0;

- /* award one bit for the contents of the fast pool */
+ /* Award one bit for the contents of the fast pool. */
credit_entropy_bits(1);
}
EXPORT_SYMBOL_GPL(add_interrupt_randomness);

-#ifdef CONFIG_BLOCK
-void add_disk_randomness(struct gendisk *disk)
-{
- if (!disk || !disk->random)
- return;
- /* first major is 1, so we get >= 0x200 here */
- add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
-}
-EXPORT_SYMBOL_GPL(add_disk_randomness);
-#endif
-
/*
* Each time the timer fires, we expect that we got an unpredictable
* jump in the cycle counter. Even if the timer is running on another
@@ -1324,73 +1477,6 @@ static void try_to_generate_entropy(void
mix_pool_bytes(&stack.now, sizeof(stack.now));
}

-static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);
-static int __init parse_trust_cpu(char *arg)
-{
- return kstrtobool(arg, &trust_cpu);
-}
-early_param("random.trust_cpu", parse_trust_cpu);
-
-/*
- * Note that setup_arch() may call add_device_randomness()
- * long before we get here. This allows seeding of the pools
- * with some platform dependent data very early in the boot
- * process. But it limits our options here. We must use
- * statically allocated structures that already have all
- * initializations complete at compile time. We should also
- * take care not to overwrite the precious per platform data
- * we were given.
- */
-int __init rand_initialize(void)
-{
- size_t i;
- ktime_t now = ktime_get_real();
- bool arch_init = true;
- unsigned long rv;
-
- for (i = 0; i < BLAKE2S_BLOCK_SIZE; i += sizeof(rv)) {
- if (!arch_get_random_seed_long_early(&rv) &&
- !arch_get_random_long_early(&rv)) {
- rv = random_get_entropy();
- arch_init = false;
- }
- mix_pool_bytes(&rv, sizeof(rv));
- }
- mix_pool_bytes(&now, sizeof(now));
- 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) {
- crng_init = 2;
- pr_notice("crng init done (trusting CPU's manufacturer)\n");
- }
-
- if (ratelimit_disable) {
- urandom_warning.interval = 0;
- unseeded_warning.interval = 0;
- }
- return 0;
-}
-
-#ifdef CONFIG_BLOCK
-void rand_initialize_disk(struct gendisk *disk)
-{
- struct timer_rand_state *state;
-
- /*
- * If kzalloc returns null, we just won't use that entropy
- * source.
- */
- state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
- if (state) {
- state->last_time = INITIAL_JIFFIES;
- disk->random = state;
- }
-}
-#endif
-
static ssize_t urandom_read(struct file *file, char __user *buf, size_t nbytes,
loff_t *ppos)
{
@@ -1685,47 +1771,3 @@ static int __init random_sysctls_init(vo
}
device_initcall(random_sysctls_init);
#endif /* CONFIG_SYSCTL */
-
-/* Interface for in-kernel drivers of true hardware RNGs.
- * Those devices may produce endless random bits and will be throttled
- * when our pool is full.
- */
-void add_hwgenerator_randomness(const void *buffer, size_t count,
- size_t entropy)
-{
- if (unlikely(crng_init == 0)) {
- size_t ret = crng_fast_load(buffer, count);
- mix_pool_bytes(buffer, ret);
- count -= ret;
- buffer += ret;
- if (!count || crng_init == 0)
- return;
- }
-
- /* Throttle writing if we're above the trickle threshold.
- * We'll be woken up again once below POOL_MIN_BITS, when
- * the calling thread is about to terminate, or once
- * CRNG_RESEED_INTERVAL has elapsed.
- */
- wait_event_interruptible_timeout(random_write_wait,
- !system_wq || kthread_should_stop() ||
- input_pool.entropy_count < POOL_MIN_BITS,
- CRNG_RESEED_INTERVAL);
- mix_pool_bytes(buffer, count);
- credit_entropy_bits(entropy);
-}
-EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
-
-/* Handle random seed passed by bootloader.
- * If the seed is trustworthy, it would be regarded as hardware RNGs. Otherwise
- * it would be regarded as device data.
- * The decision is controlled by CONFIG_RANDOM_TRUST_BOOTLOADER.
- */
-void add_bootloader_randomness(const void *buf, size_t size)
-{
- if (IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER))
- add_hwgenerator_randomness(buf, size, size * 8);
- else
- add_device_randomness(buf, size);
-}
-EXPORT_SYMBOL_GPL(add_bootloader_randomness);