linux-kernel - Re: [PATCH v5 08/11] um: use fallback for random_get

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Date:   Tue, 19 Apr 2022 13:33:21 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     "Jason A. Donenfeld" <Jason@...c4.com>,
        linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        tglx@...utronix.de, arnd@...db.de
Cc:     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>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        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>,
        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>,
        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 v5 08/11] um: use fallback for random_get_entropy()
 instead of zero

On Tue, 2022-04-19 at 13:16 +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.
> 
> This is accomplished by just including the asm-generic code like on
> other architectures, which means we can get rid of the empty stub
> function here.


LGTM, actually better than before, though not even sure any drivers in
ARCH=um have interrupts that say they can be used for this.

Acked-by: Johannes Berg <johannes@...solutions.net>

I assume you're going to take this through the random tree?

johannes