From: "Jason A. Donenfeld" Jason@zx2c4.com
commit ff8a8f59c99f6a7c656387addc4d9f2247d75077 upstream.
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 random_get_entropy_fallback() would be preferable, because that always needs to return _something_, even falling back to jiffies eventually. It's not as though random_get_entropy_fallback() 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@linutronix.de Cc: Arnd Bergmann arnd@arndb.de Reviewed-by: Russell King (Oracle) rmk+kernel@armlinux.org.uk Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm/include/asm/timex.h | 1 + 1 file changed, 1 insertion(+)
--- a/arch/arm/include/asm/timex.h +++ b/arch/arm/include/asm/timex.h @@ -14,5 +14,6 @@
typedef unsigned long cycles_t; #define get_cycles() ({ cycles_t c; read_current_timer(&c) ? 0 : c; }) +#define random_get_entropy() (((unsigned long)get_cycles()) ?: random_get_entropy_fallback())
#endif