Re: [PATCH v25 01/12] Linux Random Number Generator
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From: Nicolai Stange <hidden>
Date: 2019-11-16 18:13:29
Also in:
linux-crypto, lkml
Hi Stephan, Stephan Müller [off-list ref] 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, ...
quoted hunk
+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 <linux/errno.h> for
CONFIG_LRNG_DRNG_SWITCH=n
quoted hunk
+ } + + 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 */
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