From 3744741adab6d9195551ce30e65e726c7a408421 Mon Sep 17 00:00:00 2001 From: Willy Tarreau Date: Mon, 10 Aug 2020 10:27:42 +0200 Subject: random32: add noise from network and scheduling activity With the removal of the interrupt perturbations in previous random32 change (random32: make prandom_u32() output unpredictable), the PRNG has become 100% deterministic again. While SipHash is expected to be way more robust against brute force than the previous Tausworthe LFSR, there's still the risk that whoever has even one temporary access to the PRNG's internal state is able to predict all subsequent draws till the next reseed (roughly every minute). This may happen through a side channel attack or any data leak. This patch restores the spirit of commit f227e3ec3b5c ("random32: update the net random state on interrupt and activity") in that it will perturb the internal PRNG's statee using externally collected noise, except that it will not pick that noise from the random pool's bits nor upon interrupt, but will rather combine a few elements along the Tx path that are collectively hard to predict, such as dev, skb and txq pointers, packet length and jiffies values. These ones are combined using a single round of SipHash into a single long variable that is mixed with the net_rand_state upon each invocation. The operation was inlined because it produces very small and efficient code, typically 3 xor, 2 add and 2 rol. The performance was measured to be the same (even very slightly better) than before the switch to SipHash; on a 6-core 12-thread Core i7-8700k equipped with a 40G NIC (i40e), the connection rate dropped from 556k/s to 555k/s while the SYN cookie rate grew from 5.38 Mpps to 5.45 Mpps. Link: https://lore.kernel.org/netdev/20200808152628.GA27941@SDF.ORG/ Cc: George Spelvin Cc: Amit Klein Cc: Eric Dumazet Cc: "Jason A. Donenfeld" Cc: Andy Lutomirski Cc: Kees Cook Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Linus Torvalds Cc: tytso@mit.edu Cc: Florian Westphal Cc: Marc Plumb Tested-by: Sedat Dilek Signed-off-by: Willy Tarreau --- kernel/time/timer.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'kernel/time') diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 3e341af741b9..de37e33a868d 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -1706,6 +1706,8 @@ void update_process_times(int user_tick) { struct task_struct *p = current; + PRANDOM_ADD_NOISE(jiffies, user_tick, p, 0); + /* Note: this timer irq context must be accounted for as well. */ account_process_tick(p, user_tick); run_local_timers(); -- cgit v1.2.3