From f227e3ec3b5cad859ad15666874405e8c1bbc1d4 Mon Sep 17 00:00:00 2001 From: Willy Tarreau Date: Fri, 10 Jul 2020 15:23:19 +0200 Subject: [PATCH] random32: update the net random state on interrupt and activity This modifies the first 32 bits out of the 128 bits of a random CPU's net_rand_state on interrupt or CPU activity to complicate remote observations that could lead to guessing the network RNG's internal state. Note that depending on some network devices' interrupt rate moderation or binding, this re-seeding might happen on every packet or even almost never. In addition, with NOHZ some CPUs might not even get timer interrupts, leaving their local state rarely updated, while they are running networked processes making use of the random state. For this reason, we also perform this update in update_process_times() in order to at least update the state when there is user or system activity, since it's the only case we care about. Reported-by: Amit Klein Suggested-by: Linus Torvalds Cc: Eric Dumazet Cc: "Jason A. Donenfeld" Cc: Andy Lutomirski Cc: Kees Cook Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Signed-off-by: Willy Tarreau Signed-off-by: Linus Torvalds --- drivers/char/random.c | 1 + include/linux/random.h | 3 +++ kernel/time/timer.c | 8 ++++++++ lib/random32.c | 2 +- 4 files changed, 13 insertions(+), 1 deletion(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 2a41b21623ae42..d20ba1b104ca3a 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1277,6 +1277,7 @@ void add_interrupt_randomness(int irq, int irq_flags) fast_mix(fast_pool); add_interrupt_bench(cycles); + this_cpu_add(net_rand_state.s1, fast_pool->pool[cycles & 3]); if (unlikely(crng_init == 0)) { if ((fast_pool->count >= 64) && diff --git a/include/linux/random.h b/include/linux/random.h index 45e1f8fa742bcd..39aaa1f78f9dde 100644 --- a/include/linux/random.h +++ b/include/linux/random.h @@ -11,6 +11,7 @@ #include #include #include +#include #include @@ -119,6 +120,8 @@ struct rnd_state { __u32 s1, s2, s3, s4; }; +DECLARE_PER_CPU(struct rnd_state, net_rand_state) __latent_entropy; + u32 prandom_u32_state(struct rnd_state *state); void prandom_bytes_state(struct rnd_state *state, void *buf, size_t nbytes); void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state); diff --git a/kernel/time/timer.c b/kernel/time/timer.c index df1ff803acc4ff..026ac01af9da7e 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -43,6 +43,7 @@ #include #include #include +#include #include #include @@ -1742,6 +1743,13 @@ void update_process_times(int user_tick) scheduler_tick(); if (IS_ENABLED(CONFIG_POSIX_TIMERS)) run_posix_cpu_timers(); + + /* The current CPU might make use of net randoms without receiving IRQs + * to renew them often enough. Let's update the net_rand_state from a + * non-constant value that's not affine to the number of calls to make + * sure it's updated when there's some activity (we don't care in idle). + */ + this_cpu_add(net_rand_state.s1, rol32(jiffies, 24) + user_tick); } /** diff --git a/lib/random32.c b/lib/random32.c index 763b920a6206cd..c4d317be2997b5 100644 --- a/lib/random32.c +++ b/lib/random32.c @@ -48,7 +48,7 @@ static inline void prandom_state_selftest(void) } #endif -static DEFINE_PER_CPU(struct rnd_state, net_rand_state) __latent_entropy; +DEFINE_PER_CPU(struct rnd_state, net_rand_state) __latent_entropy; /** * prandom_u32_state - seeded pseudo-random number generator.