diff mbox series

[v2,03/11] m68k: use ktime_read_raw_clock() for random_get_entropy() instead of zero

Message ID 20220410214951.55294-4-Jason@zx2c4.com
State Superseded
Headers show
Series [v2,01/11] timekeeping: add accessor for raw clock | expand

Commit Message

Jason A. Donenfeld April 10, 2022, 9:49 p.m. UTC
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@linutronix.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 arch/m68k/include/asm/timex.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Jason A. Donenfeld April 11, 2022, 10:07 p.m. UTC | #1
Hi Thomas,

On Mon, Apr 11, 2022 at 10:18 AM Thomas Gleixner <tglx@linutronix.de> wrote:
> > 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.

Absolutely. That's a good idea. I'll do that for v3.

Jason
diff mbox series

Patch

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();
 }
 #define random_get_entropy	random_get_entropy