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Improve performance by using a lockless update mechanism suggested by

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Linus, and make sure we refresh per-CPU entropy returned get_random_*
 as soon as the CRNG is initialized.
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Merge tag 'random_for_linus_stable' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random

Pull randomness fixes from Ted Ts'o:
 "Improve performance by using a lockless update mechanism suggested by
  Linus, and make sure we refresh per-CPU entropy returned get_random_*
  as soon as the CRNG is initialized"

* tag 'random_for_linus_stable' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random:
  random: invalidate batched entropy after crng init
  random: use lockless method of accessing and updating f->reg_idx
This commit is contained in:
Linus Torvalds 2017-06-11 12:02:01 -07:00
commit 5ad9345d23
1 changed files with 43 additions and 6 deletions
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49
drivers/char/random.c
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@ -1,6 +1,9 @@
/*
* random.c -- A strong random number generator
*
* Copyright (C) 2017 Jason A. Donenfeld <Jason@zx2c4.com>. All
* Rights Reserved.
*
* Copyright Matt Mackall <mpm@selenic.com>, 2003, 2004, 2005
*
* Copyright Theodore Ts'o, 1994, 1995, 1996, 1997, 1998, 1999. All
@ -762,6 +765,8 @@ static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait);
static struct crng_state **crng_node_pool __read_mostly;
#endif
static void invalidate_batched_entropy(void);
static void crng_initialize(struct crng_state *crng)
{
int i;
@ -799,6 +804,7 @@ static int crng_fast_load(const char *cp, size_t len)
cp++; crng_init_cnt++; len--;
}
if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) {
invalidate_batched_entropy();
crng_init = 1;
wake_up_interruptible(&crng_init_wait);
pr_notice("random: fast init done\n");
@ -836,6 +842,7 @@ static void crng_reseed(struct crng_state *crng, struct entropy_store *r)
memzero_explicit(&buf, sizeof(buf));
crng->init_time = jiffies;
if (crng == &primary_crng && crng_init < 2) {
invalidate_batched_entropy();
crng_init = 2;
process_random_ready_list();
wake_up_interruptible(&crng_init_wait);
@ -1097,15 +1104,15 @@ static void add_interrupt_bench(cycles_t start)
static __u32 get_reg(struct fast_pool *f, struct pt_regs *regs)
{
__u32 *ptr = (__u32 *) regs;
unsigned long flags;
unsigned int idx;
if (regs == NULL)
return 0;
local_irq_save(flags);
if (f->reg_idx >= sizeof(struct pt_regs) / sizeof(__u32))
f->reg_idx = 0;
ptr += f->reg_idx++;
local_irq_restore(flags);
idx = READ_ONCE(f->reg_idx);
if (idx >= sizeof(struct pt_regs) / sizeof(__u32))
idx = 0;
ptr += idx++;
WRITE_ONCE(f->reg_idx, idx);
return *ptr;
}
@ -2023,6 +2030,7 @@ struct batched_entropy {
};
unsigned int position;
};
static rwlock_t batched_entropy_reset_lock = __RW_LOCK_UNLOCKED(batched_entropy_reset_lock);
/*
* Get a random word for internal kernel use only. The quality of the random
@ -2033,6 +2041,8 @@ static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u64);
u64 get_random_u64(void)
{
u64 ret;
bool use_lock = crng_init < 2;
unsigned long flags;
struct batched_entropy *batch;
#if BITS_PER_LONG == 64
@ -2045,11 +2055,15 @@ u64 get_random_u64(void)
#endif
batch = &get_cpu_var(batched_entropy_u64);
if (use_lock)
read_lock_irqsave(&batched_entropy_reset_lock, flags);
if (batch->position % ARRAY_SIZE(batch->entropy_u64) == 0) {
extract_crng((u8 *)batch->entropy_u64);
batch->position = 0;
}
ret = batch->entropy_u64[batch->position++];
if (use_lock)
read_unlock_irqrestore(&batched_entropy_reset_lock, flags);
put_cpu_var(batched_entropy_u64);
return ret;
}
@ -2059,22 +2073,45 @@ static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u32);
u32 get_random_u32(void)
{
u32 ret;
bool use_lock = crng_init < 2;
unsigned long flags;
struct batched_entropy *batch;
if (arch_get_random_int(&ret))
return ret;
batch = &get_cpu_var(batched_entropy_u32);
if (use_lock)
read_lock_irqsave(&batched_entropy_reset_lock, flags);
if (batch->position % ARRAY_SIZE(batch->entropy_u32) == 0) {
extract_crng((u8 *)batch->entropy_u32);
batch->position = 0;
}
ret = batch->entropy_u32[batch->position++];
if (use_lock)
read_unlock_irqrestore(&batched_entropy_reset_lock, flags);
put_cpu_var(batched_entropy_u32);
return ret;
}
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
* simply resetting the counter to zero so that it's re-extracted on the
* next usage. */
static void invalidate_batched_entropy(void)
{
int cpu;
unsigned long flags;
write_lock_irqsave(&batched_entropy_reset_lock, flags);
for_each_possible_cpu (cpu) {
per_cpu_ptr(&batched_entropy_u32, cpu)->position = 0;
per_cpu_ptr(&batched_entropy_u64, cpu)->position = 0;
}
write_unlock_irqrestore(&batched_entropy_reset_lock, flags);
}
/**
* randomize_page - Generate a random, page aligned address
* @start: The smallest acceptable address the caller will take.