In the event that random_get_entropy() can't access a cycle counter or similar, falling back to returning 0 is really not the best we can do. Instead, at least calling sched_clock() would be preferable, because that always needs to return _something_, even falling back to jiffies eventually. It's not as though sched_clock() is super high precision or guaranteed to be entropic, but basically anything that's not zero all the time is better than returning zero all the time. If CONFIG_ARM_ARCH_TIMER=n, then get_cycles() will return 0, so we only need the fallback code for that case. Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> Cc: Will Deacon <will@xxxxxxxxxx> Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx> --- arch/arm64/include/asm/timex.h | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/arch/arm64/include/asm/timex.h b/arch/arm64/include/asm/timex.h index cf59ce91b22d..bfebd2e1ce45 100644 --- a/arch/arm64/include/asm/timex.h +++ b/arch/arm64/include/asm/timex.h @@ -13,6 +13,15 @@ */ #define get_cycles() arch_timer_read_counter() +#ifndef CONFIG_ARM_ARCH_TIMER +/* + * The default implementation of random_get_entropy() calls get_cycles(), + * which will return 0 if CONFIG_ARM_ARCH_TIMER=n, so we fall back to + * sched_clock() here. Not a great situation, but better than nothing. + */ +#define random_get_entropy() ((unsigned long)sched_clock()) +#endif + #include <asm-generic/timex.h> #endif -- 2.35.1
