Messages in this thread Patch in this message | | | From | "Jason A. Donenfeld" <> | Subject | [PATCH RFC v1 05/10] arm: use sched_clock() for random_get_entropy() instead of zero | Date | Fri, 8 Apr 2022 20:21:40 +0200 |
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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.
Cc: Arnd Bergmann <arnd@arndb.de> Cc: Russell King <linux@armlinux.org.uk> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> --- arch/arm/include/asm/timex.h | 11 +++++++++++ 1 file changed, 11 insertions(+)
diff --git a/arch/arm/include/asm/timex.h b/arch/arm/include/asm/timex.h index 7c3b3671d6c2..1c51580ee55d 100644 --- a/arch/arm/include/asm/timex.h +++ b/arch/arm/include/asm/timex.h @@ -9,7 +9,18 @@ #ifndef _ASMARM_TIMEX_H #define _ASMARM_TIMEX_H +#include <linux/sched/clock.h> + typedef unsigned long cycles_t; #define get_cycles() ({ cycles_t c; read_current_timer(&c) ? 0 : c; }) +static inline unsigned long random_get_entropy(void) +{ + unsigned long ret = get_cycles(); + if (ret) + return ret; + return sched_clock(); +} +#define random_get_entropy random_get_entropy + #endif -- 2.35.1
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