In the event that a given arch does not define get_cycles(), falling back to the get_cycles() default implementation that returns 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. Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: Theodore Ts'o <tytso@xxxxxxx> Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx> --- include/linux/timex.h | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/include/linux/timex.h b/include/linux/timex.h index 5745c90c8800..bd78f784762e 100644 --- a/include/linux/timex.h +++ b/include/linux/timex.h @@ -61,6 +61,7 @@ #include <linux/compiler.h> #include <linux/types.h> #include <linux/param.h> +#include <linux/sched/clock.h> #include <asm/timex.h> @@ -74,8 +75,13 @@ * * By default we use get_cycles() for this purpose, but individual * architectures may override this in their asm/timex.h header file. + * If a given arch does not have get_cycles(), then we fallback to + * using sched_clock(). */ +#ifdef get_cycles #define random_get_entropy() ((unsigned long)get_cycles()) +#else +#define random_get_entropy() ((unsigned long)sched_clock()) #endif /* -- 2.35.1
