Am Sun, May 01, 2022 at 02:38:49PM +0200 schrieb Jason A. Donenfeld: > Since the RNG loses freshness system suspend/hibernation, when we > resume, immediately reseed using whatever data we can, which for this > particular case is the various timestamps regarding system suspend time, > in addition to more generally the RDSEED/RDRAND/RDTSC values that happen > whenever the crng reseeds. > > On systems that suspend and resume automatically all the time -- such as > Android -- we skip the reseeding on suspend resumption, since that could > wind up being far too busy. This is the same trade-off made in > WireGuard. > > In addition to reseeding upon resumption always mix into the pool these > various stamps on every power notification event. > > Cc: Theodore Ts'o <tytso@xxxxxxx> > Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx> > --- > drivers/char/random.c | 34 ++++++++++++++++++++++++++++++++++ > 1 file changed, 34 insertions(+) > > diff --git a/drivers/char/random.c b/drivers/char/random.c > index 0935a140795e..48eac27214ea 100644 > --- a/drivers/char/random.c > +++ b/drivers/char/random.c > @@ -53,6 +53,7 @@ > #include <linux/completion.h> > #include <linux/uuid.h> > #include <linux/uaccess.h> > +#include <linux/suspend.h> > #include <crypto/chacha.h> > #include <crypto/blake2s.h> > #include <asm/processor.h> > @@ -966,6 +967,37 @@ static int __init parse_trust_bootloader(char *arg) > early_param("random.trust_cpu", parse_trust_cpu); > early_param("random.trust_bootloader", parse_trust_bootloader); > > +static int random_pm_notification(struct notifier_block *nb, unsigned long action, void *data) > +{ > + unsigned long flags, entropy = random_get_entropy(); > + > + /* > + * Encode a representation of how long the system has been suspended, > + * in a way that is distinct from prior system suspends. > + */ > + ktime_t stamps[] = { > + ktime_get(), > + ktime_get_boottime(), > + ktime_get_real() > + }; > + > + spin_lock_irqsave(&input_pool.lock, flags); > + _mix_pool_bytes(&action, sizeof(action)); > + _mix_pool_bytes(stamps, sizeof(stamps)); > + _mix_pool_bytes(&entropy, sizeof(entropy)); > + spin_unlock_irqrestore(&input_pool.lock, flags); > + > + if (action == PM_RESTORE_PREPARE || > + (action == PM_POST_SUSPEND && > + !IS_ENABLED(CONFIG_PM_AUTOSLEEP) && !IS_ENABLED(CONFIG_ANDROID))) { > + crng_reseed(true); > + pr_notice("crng reseeded on system resumption\n"); > + } > + return 0; > +} Should this also wake up any thread waiting in add_hwgenerator_randomness() / "use" the input already in store there? Thanks, Dominik