From: Nicolai Stange Subject: Re: [PATCH v25 01/12] Linux Random Number Generator Date: Sat, 16 Nov 2019 19:13:23 +0100 Message-ID: <87mucvadvg.fsf@suse.de> References: <6157374.ptSnyUpaCn@positron.chronox.de> <2787174.DQlWHN5GGo@positron.chronox.de> <2645285.kI0haNqfm4@positron.chronox.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Return-path: In-Reply-To: <2645285.kI0haNqfm4@positron.chronox.de> ("Stephan \=\?utf-8\?Q\?M\=C3\=BCller\=22's\?\= message of "Sat, 16 Nov 2019 10:33:20 +0100") Sender: linux-kernel-owner@vger.kernel.org To: Stephan =?utf-8?Q?M=C3=BCller?= Cc: Arnd Bergmann , Greg Kroah-Hartman , linux-crypto@vger.kernel.org, LKML , linux-api@vger.kernel.org, "Eric W. Biederman" , "Alexander E. Patrakov" , "Ahmed S. Darwish" , "Theodore Y. Ts'o" , Willy Tarreau , Matthew Garrett , Vito Caputo , Andreas Dilger , Jan Kara , Ray Strode , William Jon McCann , zhangjs , Andy Lutomirski , Florian Weimer , Lennart Poettering , Nicolai Stange List-Id: linux-api@vger.kernel.org Hi Stephan, Stephan Müller writes: > +/* Initialize the default DRNG during boot */ I think that this can get called a bit too early through the get_random_bytes() invoked from e.g. boot_init_stack_canary(): in start_kernel(), there is boot_init_stack_canary(); time_init(); On ARM (at least with arm_arch_timer.c), get_cycles() would return 0 until time_init() => timer_probe() => arch_timer_of_init() => arch_timer_common_init() => arch_timer_arch_init() => arch_timer_delay_timer_register() => register_current_timer_delay() has executed and thus, ... > +void lrng_drngs_init_cc20(void) > +{ > + unsigned long flags = 0; > + > + if (lrng_get_available()) > + return; > + > + lrng_sdrng_lock(&lrng_sdrng_init, &flags); > + if (lrng_get_available()) { > + lrng_sdrng_unlock(&lrng_sdrng_init, &flags); > + return; > + } > + > + if (random_get_entropy() || random_get_entropy()) { > + /* > + * As the highres timer is identified here, previous interrupts > + * obtained during boot time are treated like a lowres-timer > + * would have been present. > + */ > + lrng_pool_configure(true, LRNG_IRQ_ENTROPY_BITS); > + } else { > + lrng_health_disable(); > + lrng_pool_configure(false, LRNG_IRQ_ENTROPY_BITS * > + LRNG_IRQ_OVERSAMPLING_FACTOR); > + pr_warn("operating without high-resolution timer and applying " > + "IRQ oversampling factor %u\n", > + LRNG_IRQ_OVERSAMPLING_FACTOR); ... LRNG thinks that no high-res timer is available even though there is: [ 0.000000] lrng_sdrng: operating without high-resolution timer and applying IRQ oversampling factor 10 [ 0.000000] lrng_chacha20: ChaCha20 core initialized [ 0.000000] lrng_chacha20: ChaCha20 core initialized [ 0.000014] sched_clock: 32 bits at 1000kHz, resolution 1000ns, wraps every 2147483647500ns [ 0.000036] clocksource: timer: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 1911260446275 ns [ 0.000114] bcm2835: system timer (irq = 27) [ 0.000594] arch_timer: cp15 timer(s) running at 19.20MHz (phys). [ 0.000613] clocksource: arch_sys_counter: mask: 0xffffffffffffff max_cycles: 0x46d987e47, max_idle_ns: 440795202767 ns [ 0.000631] sched_clock: 56 bits at 19MHz, resolution 52ns, wraps every 4398046511078ns [ 0.000645] Switching to timer-based delay loop, resolution 52ns Note that this last line comes from aforementioned register_current_timer_delay(). Similarly, get_random_bytes() can get called quite early through WARN() => warn_slowpath_fmt() => __warn() => print_oops_end_marker() => init_oops_id(). Perhaps it would make sense not to do the (pool + health test) initalization "on-demand", but rather make sure it happens at some well-defined point after time_init()? Or at least that the pool + the health tests get reconfigured eventually? Thanks, Nicolai P.S: include/linux/lrng.h needs an #include for CONFIG_LRNG_DRNG_SWITCH=n > + } > + > + lrng_sdrng_reset(&lrng_sdrng_init); > + lrng_cc20_init_state(&secondary_chacha20); > + lrng_state_init_seed_work(); > + lrng_sdrng_unlock(&lrng_sdrng_init, &flags); > + > + lrng_sdrng_lock(&lrng_sdrng_atomic, &flags); > + lrng_sdrng_reset(&lrng_sdrng_atomic); > + /* > + * We do not initialize the state of the atomic DRNG as it is identical > + * to the secondary DRNG at this point. > + */ > + lrng_sdrng_unlock(&lrng_sdrng_atomic, &flags); > + > + lrng_trng_init(); > + > + lrng_set_available(); > +} > + > +/* Reset LRNG such that all existing entropy is gone */ -- SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg), GF: Felix Imendörffer