This is a note to let you know that I've just added the patch titled
random: use static branch for crng_ready()
to the 5.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
random-use-static-branch-for-crng_ready.patch
and it can be found in the queue-5.18 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Thu May 26 04:17:01 PM CEST 2022
From: "Jason A. Donenfeld" <Jason@xxxxxxxxx>
Date: Tue, 3 May 2022 15:30:45 +0200
Subject: random: use static branch for crng_ready()
From: "Jason A. Donenfeld" <Jason@xxxxxxxxx>
commit f5bda35fba615ace70a656d4700423fa6c9bebee upstream.
Since crng_ready() is only false briefly during initialization and then
forever after becomes true, we don't need to evaluate it after, making
it a prime candidate for a static branch.
One complication, however, is that it changes state in a particular call
to credit_init_bits(), which might be made from atomic context, which
means we must kick off a workqueue to change the static key. Further
complicating things, credit_init_bits() may be called sufficiently early
on in system initialization such that system_wq is NULL.
Fortunately, there exists the nice function execute_in_process_context(),
which will immediately execute the function if !in_interrupt(), and
otherwise defer it to a workqueue. During early init, before workqueues
are available, in_interrupt() is always false, because interrupts
haven't even been enabled yet, which means the function in that case
executes immediately. Later on, after workqueues are available,
in_interrupt() might be true, but in that case, the work is queued in
system_wq and all goes well.
Cc: Theodore Ts'o <tytso@xxxxxxx>
Cc: Sultan Alsawaf <sultan@xxxxxxxxxxxxxxx>
Reviewed-by: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/char/random.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -77,8 +77,9 @@ static enum {
CRNG_EMPTY = 0, /* Little to no entropy collected */
CRNG_EARLY = 1, /* At least POOL_EARLY_BITS collected */
CRNG_READY = 2 /* Fully initialized with POOL_READY_BITS collected */
-} crng_init = CRNG_EMPTY;
-#define crng_ready() (likely(crng_init >= CRNG_READY))
+} crng_init __read_mostly = CRNG_EMPTY;
+static DEFINE_STATIC_KEY_FALSE(crng_is_ready);
+#define crng_ready() (static_branch_likely(&crng_is_ready) || crng_init >= CRNG_READY)
/* Various types of waiters for crng_init->CRNG_READY transition. */
static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait);
static struct fasync_struct *fasync;
@@ -108,6 +109,11 @@ bool rng_is_initialized(void)
}
EXPORT_SYMBOL(rng_is_initialized);
+static void crng_set_ready(struct work_struct *work)
+{
+ static_branch_enable(&crng_is_ready);
+}
+
/* Used by wait_for_random_bytes(), and considered an entropy collector, below. */
static void try_to_generate_entropy(void);
@@ -267,7 +273,7 @@ static void crng_reseed(void)
++next_gen;
WRITE_ONCE(base_crng.generation, next_gen);
WRITE_ONCE(base_crng.birth, jiffies);
- if (!crng_ready())
+ if (!static_branch_likely(&crng_is_ready))
crng_init = CRNG_READY;
spin_unlock_irqrestore(&base_crng.lock, flags);
memzero_explicit(key, sizeof(key));
@@ -785,6 +791,7 @@ static void extract_entropy(void *buf, s
static void credit_init_bits(size_t nbits)
{
+ static struct execute_work set_ready;
unsigned int new, orig, add;
unsigned long flags;
@@ -800,6 +807,7 @@ static void credit_init_bits(size_t nbit
if (orig < POOL_READY_BITS && new >= POOL_READY_BITS) {
crng_reseed(); /* Sets crng_init to CRNG_READY under base_crng.lock. */
+ execute_in_process_context(crng_set_ready, &set_ready);
process_random_ready_list();
wake_up_interruptible(&crng_init_wait);
kill_fasync(&fasync, SIGIO, POLL_IN);
@@ -1348,7 +1356,7 @@ SYSCALL_DEFINE3(getrandom, char __user *
if (count > INT_MAX)
count = INT_MAX;
- if (!(flags & GRND_INSECURE) && !crng_ready()) {
+ if (!crng_ready() && !(flags & GRND_INSECURE)) {
int ret;
if (flags & GRND_NONBLOCK)
Patches currently in stable-queue which might be from Jason@xxxxxxxxx are
queue-5.18/random-remove-ratelimiting-for-in-kernel-unseeded-randomness.patch
queue-5.18/random-fix-sysctl-documentation-nits.patch
queue-5.18/random-help-compiler-out-with-fast_mix-by-using-simpler-arguments.patch
queue-5.18/siphash-use-one-source-of-truth-for-siphash-permutations.patch
queue-5.18/um-use-fallback-for-random_get_entropy-instead-of-zero.patch
queue-5.18/random-order-timer-entropy-functions-below-interrupt-functions.patch
queue-5.18/random-unify-batched-entropy-implementations.patch
queue-5.18/random-make-consistent-use-of-buf-and-len.patch
queue-5.18/random-move-randomize_page-into-mm-where-it-belongs.patch
queue-5.18/random-use-first-128-bits-of-input-as-fast-init.patch
queue-5.18/random-use-proper-return-types-on-get_random_-int-long-_wait.patch
queue-5.18/s390-define-get_cycles-macro-for-arch-override.patch
queue-5.18/timekeeping-add-raw-clock-fallback-for-random_get_entropy.patch
queue-5.18/random-use-static-branch-for-crng_ready.patch
queue-5.18/arm-use-fallback-for-random_get_entropy-instead-of-zero.patch
queue-5.18/mips-use-fallback-for-random_get_entropy-instead-of-just-c0-random.patch
queue-5.18/random-avoid-initializing-twice-in-credit-race.patch
queue-5.18/random-move-initialization-functions-out-of-hot-pages.patch
queue-5.18/random-do-not-pretend-to-handle-premature-next-security-model.patch
queue-5.18/random-do-not-use-batches-when-crng_ready.patch
queue-5.18/m68k-use-fallback-for-random_get_entropy-instead-of-zero.patch
queue-5.18/random-move-initialization-out-of-reseeding-hot-path.patch
queue-5.18/x86-tsc-use-fallback-for-random_get_entropy-instead-of-zero.patch
queue-5.18/random-credit-architectural-init-the-exact-amount.patch
queue-5.18/random-check-for-signals-after-page-of-pool-writes.patch
queue-5.18/random-remove-extern-from-functions-in-header.patch
queue-5.18/random-do-not-use-input-pool-from-hard-irqs.patch
queue-5.18/random-wire-up-fops-splice_-read-write-_iter.patch
queue-5.18/random-insist-on-random_get_entropy-existing-in-order-to-simplify.patch
queue-5.18/powerpc-define-get_cycles-macro-for-arch-override.patch
queue-5.18/parisc-define-get_cycles-macro-for-arch-override.patch
queue-5.18/sparc-use-fallback-for-random_get_entropy-instead-of-zero.patch
queue-5.18/nios2-use-fallback-for-random_get_entropy-instead-of-zero.patch
queue-5.18/init-call-time_init-before-rand_initialize.patch
queue-5.18/riscv-use-fallback-for-random_get_entropy-instead-of-zero.patch
queue-5.18/ia64-define-get_cycles-macro-for-arch-override.patch
queue-5.18/random-handle-latent-entropy-and-command-line-from-random_init.patch
queue-5.18/random-use-proper-jiffies-comparison-macro.patch
queue-5.18/alpha-define-get_cycles-macro-for-arch-override.patch
queue-5.18/random-convert-to-using-fops-read_iter.patch
queue-5.18/xtensa-use-fallback-for-random_get_entropy-instead-of-zero.patch
queue-5.18/random-use-symbolic-constants-for-crng_init-states.patch
queue-5.18/random-convert-to-using-fops-write_iter.patch
