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Subject[PATCH 4.14 104/237] random: tie batched entropy generation to base_crng generation
Date
From: "Jason A. Donenfeld" <Jason@zx2c4.com>

commit 0791e8b655cc373718f0f58800fdc625a3447ac5 upstream.

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: Eric Biggers <ebiggers@google.com>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/char/random.c | 29 ++++++++---------------------
1 file changed, 8 insertions(+), 21 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -428,8 +428,6 @@ 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
@@ -452,7 +450,7 @@ static size_t crng_fast_load(const void
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);
@@ -529,7 +527,6 @@ 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;
}
@@ -1254,8 +1251,9 @@ 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");
}
@@ -1593,8 +1591,6 @@ struct ctl_table random_table[] = {
};
#endif /* CONFIG_SYSCTL */

-static atomic_t batch_generation = ATOMIC_INIT(0);
-
struct batched_entropy {
union {
/*
@@ -1607,8 +1603,8 @@ struct batched_entropy {
u64 entropy_u64[CHACHA20_BLOCK_SIZE * 3 / (2 * sizeof(u64))];
u32 entropy_u32[CHACHA20_BLOCK_SIZE * 3 / (2 * sizeof(u32))];
};
+ unsigned long generation;
unsigned int position;
- int generation;
};

/*
@@ -1627,14 +1623,14 @@ 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_irq_save(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));
@@ -1660,14 +1656,14 @@ 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_irq_save(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));
@@ -1683,15 +1679,6 @@ 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.

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