| Message ID | 20220413115411.21489-7-Jason@zx2c4.com |
|---|---|
| State | New |
| Headers | show |
| Series | archs/random: fallback to best raw ktime when no cycle counter | expand |
On 4/13/22 06:54, Jason A. Donenfeld wrote: > 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> > Cc: Dinh Nguyen <dinguyen@kernel.org> > Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> > --- > arch/nios2/include/asm/timex.h | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/arch/nios2/include/asm/timex.h b/arch/nios2/include/asm/timex.h > index a769f871b28d..d9a3f426cdda 100644 > --- a/arch/nios2/include/asm/timex.h > +++ b/arch/nios2/include/asm/timex.h > @@ -9,4 +9,6 @@ typedef unsigned long cycles_t; > > extern cycles_t get_cycles(void); > > +#define random_get_entropy() (((unsigned long)get_cycles()) ?: random_get_entropy_fallback()) > + > #endif Acked-by: Dinh Nguyen <dinguyen@kernel.org>
diff --git a/arch/nios2/include/asm/timex.h b/arch/nios2/include/asm/timex.h index a769f871b28d..d9a3f426cdda 100644 --- a/arch/nios2/include/asm/timex.h +++ b/arch/nios2/include/asm/timex.h @@ -9,4 +9,6 @@ typedef unsigned long cycles_t; extern cycles_t get_cycles(void); +#define random_get_entropy() (((unsigned long)get_cycles()) ?: random_get_entropy_fallback()) + #endif
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> Cc: Dinh Nguyen <dinguyen@kernel.org> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> --- arch/nios2/include/asm/timex.h | 2 ++ 1 file changed, 2 insertions(+)