linux-kernel - Re: [PATCH v6 12/17] nios2: use fallback for random_get

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Message-ID: <1a6535c7-df9c-1e08-8818-b8cd2c6d8fc2@kernel.org>
Date:   Mon, 23 May 2022 08:56:56 -0500
From:   Dinh Nguyen <dinguyen@...nel.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>,
        linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        tglx@...utronix.de, arnd@...db.de
Subject: Re: [PATCH v6 12/17] nios2: use fallback for random_get_entropy()
 instead of zero



On 4/23/22 16:26, 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@...utronix.de>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Dinh Nguyen <dinguyen@...nel.org>
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> ---
>   arch/nios2/include/asm/timex.h | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/arch/nios2/include/asm/timex.h b/arch/nios2/include/asm/timex.h
> index a769f871b28d..40a1adc9bd03 100644
> --- a/arch/nios2/include/asm/timex.h
> +++ b/arch/nios2/include/asm/timex.h
> @@ -8,5 +8,8 @@
>   typedef unsigned long cycles_t;
>   
>   extern cycles_t get_cycles(void);
> +#define get_cycles get_cycles
> +
> +#define random_get_entropy() (((unsigned long)get_cycles()) ?: random_get_entropy_fallback())
>   
>   #endif

Acked-by: Dinh Nguyen <dinguyen@...nel.org>