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
