linux-kernel - Re: [PATCH v5 11/11] random: insist on random_get

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Message-ID: <YmPOQS9GvdiM2brX@zx2c4.com>
Date:   Sat, 23 Apr 2022 12:00:33 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Sandy Harris <sandyinchina@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Arnd Bergmann <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>,
        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>,
        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>,
        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 11/11] random: insist on random_get_entropy() existing
 in order to simplify

Hi Sandy,

On Sat, Apr 23, 2022 at 10:24:07AM +0800, Sandy Harris wrote:
> On Sat, Apr 23, 2022 at 6:37 AM Jason A. Donenfeld <Jason@...c4.com> wrote:
> >
> > All platforms are now guaranteed to provide some value for
> > random_get_entropy(). In case some bug leads to this not being so, we
> > print a warning, ...
> 
> Would it make sense to test at compile time? If there is no hardware
> RNG nor a cycle counter, then the kernel should be compiled with
> the gcc latent entropy plugin. Generate a warning suggesting that,
> or even an error insisting on it.

Unfortunately, as a last ditch warning safeguard against bugs, I don't
think that's something we can determine at build time. A lot of this
machinery is dynamic. Fortunately a single check at init time brings
with it zero appreciable overhead.

Jason