linux-kernel - Re: [PATCH v4 04/11] mips: use fallback for random_get

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Message-ID: <20220413122546.GA11860@alpha.franken.de>
Date:   Wed, 13 Apr 2022 14:25:46 +0200
From:   Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        tglx@...utronix.de, arnd@...db.de, Theodore Ts'o <tytso@....edu>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        "David S . Miller" <davem@...emloft.net>,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Johannes Berg <johannes@...solutions.net>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H . Peter Anvin" <hpa@...or.com>, Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        John Stultz <john.stultz@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Dinh Nguyen <dinguyen@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-m68k@...ts.linux-m68k.org, linux-mips@...r.kernel.org,
        linux-riscv@...ts.infradead.org, sparclinux@...r.kernel.org,
        linux-um@...ts.infradead.org, x86@...nel.org,
        linux-xtensa@...ux-xtensa.org
Subject: Re: [PATCH v4 04/11] mips: use fallback for random_get_entropy()
 instead of zero

On Wed, Apr 13, 2022 at 01:54:04PM +0200, 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: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> ---
>  arch/mips/include/asm/timex.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/mips/include/asm/timex.h b/arch/mips/include/asm/timex.h
> index b05bb70a2e46..abc60a6395e3 100644
> --- a/arch/mips/include/asm/timex.h
> +++ b/arch/mips/include/asm/timex.h
> @@ -94,7 +94,7 @@ static inline unsigned long random_get_entropy(void)
>  	else if (likely(imp != PRID_IMP_R6000 && imp != PRID_IMP_R6000A))
>  		return read_c0_random();
>  	else
> -		return 0;	/* no usable register */
> +		return random_get_entropy_fallback();	/* no usable register */
>  }
>  #define random_get_entropy random_get_entropy
>  
> -- 
> 2.35.1

Acked-by: Thomas Bogendoerfer <tsbogend@...ha.franken.de>

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]