2022-04-19 15:54:37

by Jason A. Donenfeld

Subject: [PATCH v5 06/11] nios2: use fallback for random_get_entropy() instead of zero

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 <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Dinh Nguyen <[email protected]>
Signed-off-by: Jason A. Donenfeld <[email protected]>
---
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
--
2.35.1

2022-05-02 23:57:50

by Dinh Nguyen

Subject: Re: [PATCH v5 06/11] nios2: use fallback for random_get_entropy() instead of zero

On 4/19/22 06:16, 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 <[email protected]>
> Cc: Arnd Bergmann <[email protected]>
> Cc: Dinh Nguyen <[email protected]>
> Signed-off-by: Jason A. Donenfeld <[email protected]>
> ---
> 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 <[email protected]>