linux-kernel - Re: [PATCH RFC v0] random: block in /dev/urandom

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Date:   Mon, 14 Feb 2022 15:26:24 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Joshua Kinard <kumba@...too.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@...r.kernel.org>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Eric Biggers <ebiggers@...gle.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Lennart Poettering <mzxreary@...inter.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Theodore Ts'o" <tytso@....edu>
Subject: Re: [PATCH RFC v0] random: block in /dev/urandom

Hi Jason,

On Mon, Feb 14, 2022 at 3:05 PM Jason A. Donenfeld <Jason@...c4.com> wrote:
> On Sun, Feb 13, 2022 at 12:06 AM Joshua Kinard <kumba@...too.org> wrote:
> > The R6000/R6000A CPU only ever existed in systems in the late 1980's that
> > were fairly large, and I don't think there is a complete, working unit out
> > there that can actually boot up, let alone boot a Linux kernel.
>
> So from what you've written, it sounds like MIPS is actually not a problem here.
>
> So the only systems we're actually talking about without a good cycle
> counter are non-Amiga m68k? If so, that'd be a pretty terrific
> finding. It'd mean that this idea can move forward, and we only need
> to worry about some m68k museum pieces with misconfigured
> userspaces...

I'm afraid you missed one important detail.  You wrote:

> On every platform, random_get_entropy() is connected to get_cycles(),
> except for three: m68k, MIPS, and RISC-V.

The default implementation in include/asm-generic/timex.h is:

    static inline cycles_t get_cycles(void)
    {
            return 0;
    }

Several architectures do not implement get_cycles(), or implement it
with a variant that's very similar or identical to the generic version.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds