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authorLinus Torvalds <torvalds@linux-foundation.org>2017-06-11 12:02:01 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-06-11 12:02:01 -0700
commit5ad9345d2321eb1442794098506d136d01cf8345 (patch)
tree500c5274cf0433c7266c901727b722315508c358 /drivers/char
parent5e38b72ac1b0000f1d7bd2b62fba7ee9053f5b94 (diff)
parentb169c13de473a85b3c859bb36216a4cb5f00a54a (diff)
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
Diffstat (limited to 'drivers/char')
-rw-r--r--drivers/char/random.c49
1 files changed, 43 insertions, 6 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c
index a561f0c2f428..e870f329db88 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -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.