| Message ID | 20220215211333.244383-1-Jason@zx2c4.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Delegated to: | Herbert Xu |
| Headers | show |
| Series | [v3] random: absorb fast pool into input pool after fast load | expand |
On Tue, Feb 15, 2022 at 10:13:33PM +0100, Jason A. Donenfeld wrote: > During crng_init == 0, we never credit entropy in add_interrupt_ > randomness(), but instead dump it directly into the primary_crng. That's > fine, except for the fact that we then wind up throwing away that > entropy later when we switch to extracting from the input pool and > overwriting the primary_crng key. The two other early init sites -- > add_hwgenerator_randomness()'s use crng_fast_load() and add_device_ > randomness()'s use of crng_slow_load() -- always additionally give their > inputs to the input pool. But not add_interrupt_randomness(). > > This commit fixes that shortcoming by calling mix_pool_bytes() after > crng_fast_load() in add_interrupt_randomness(). That's partially > verboten on PREEMPT_RT, where it implies taking spinlock_t from an IRQ > handler. But this also only happens during early boot and then never > again after that. Plus it's a trylock so it has the same considerations > as calling crng_fast_load(), which we're already using. > > Cc: Theodore Ts'o <tytso@mit.edu> > Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net> > Suggested-by: Eric Biggers <ebiggers@google.com> > Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> > --- > v3 uses a trylock instead of a spinlock, just like all the other locks > taken in hard irq. (Incidentally, we're now talking about moving this > into the deferred stage, so that at can be a spinlock, but at least with > what we have here, this really must be a trylock.) This looks fine, though it's unfortunate that it has to be a trylock so this isn't guaranteed. Also, the commit message is a bit misleading because it talks about "overwriting" the primary_crng key, but at this point in the series the extracted entropy is still being XOR'd with the primary_crng key. It's not until the next patch that the key is simply overwritten. - Eric
On Mon, Feb 21, 2022 at 3:47 AM Eric Biggers <ebiggers@kernel.org> wrote: > This looks fine, though it's unfortunate that it has to be a trylock so this > isn't guaranteed. Also, the commit message is a bit misleading because it talks > about "overwriting" the primary_crng key, but at this point in the series the > extracted entropy is still being XOR'd with the primary_crng key. It's not > until the next patch that the key is simply overwritten. I'll fix up the commit message.
diff --git a/drivers/char/random.c b/drivers/char/random.c index d31b0b3afe2e..f3179c67010b 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -850,6 +850,10 @@ void add_interrupt_randomness(int irq) crng_fast_load((u8 *)fast_pool->pool, sizeof(fast_pool->pool)) > 0) { fast_pool->count = 0; fast_pool->last = now; + if (spin_trylock(&input_pool.lock)) { + _mix_pool_bytes(&fast_pool->pool, sizeof(fast_pool->pool)); + spin_unlock(&input_pool.lock); + } } return; }