On Sun, Apr 10 2022 at 23:49, 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 ktime_read_raw_clock() would be preferable,
> because that always needs to return _something_, even falling back to
> jiffies eventually. It's not as though ktime_read_raw_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: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
> ---
> arch/m68k/include/asm/timex.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/m68k/include/asm/timex.h b/arch/m68k/include/asm/timex.h
> index 6a21d9358280..5351b10e1b18 100644
> --- a/arch/m68k/include/asm/timex.h
> +++ b/arch/m68k/include/asm/timex.h
> @@ -35,7 +35,7 @@ static inline unsigned long random_get_entropy(void)
> {
> if (mach_random_get_entropy)
> return mach_random_get_entropy();
> - return 0;
> + return ktime_read_raw_clock();
I'd rather do something like this in a common header:
unsigned long random_get_entropy_fallback(void);
and use random_get_entropy_fallback() in the architecture specific
files.
That way you can encapsulate the fallback implementation in the random
code and if it turns out that ktime_read_raw_clock() is a stupid idea or
someone has a better idea then you have to change exactly one place and
not patch the whole tree again.
Thanks,
tglx
