linux-kernel - Re: [PATCH] random: add rng-seed= command line option

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Date:   Fri, 7 Feb 2020 10:58:28 -0500
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Mark Salyzyn <salyzyn@...roid.com>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Richard Henderson <richard.henderson@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Hsin-Yi Wang <hsinyi@...omium.org>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexander Potapenko <glider@...gle.com>
Subject: Re: [PATCH] random: add rng-seed= command line option

What was the base of your patch?  It's not applying on my kernel tree.

On Fri, Feb 07, 2020 at 07:07:59AM -0800, Mark Salyzyn wrote:
> A followup to commit 428826f5358c922dc378830a1717b682c0823160
> ("fdt: add support for rng-seed") to extend what was started
> with Open Firmware (OF or Device Tree) parsing, but also add
> it to the command line.
> 
> If CONFIG_RANDOM_TRUST_BOOTLOADER is set, then feed the rng-seed
> command line option length as added trusted entropy.
> 
> Always rrase all views of the rng-seed option, except early command
> line parsing, to prevent leakage to applications or modules, to
> eliminate any attack vector.

s/rrase/erase/

> 
> It is preferred to add rng-seed to the Device Tree, but some
> platforms do not have this option, so this adds the ability to
> provide some command-line-limited data to the entropy through this
> alternate mechanism.  Expect all 8 bits to be used, but must exclude
> space to be accounted in the command line.

"all 8 bits"?

> @@ -875,6 +909,21 @@ asmlinkage __visible void __init start_kernel(void)
>  	rand_initialize();
>  	add_latent_entropy();
>  	add_device_randomness(command_line, strlen(command_line));
> +	if (IS_BUILTIN(CONFIG_RANDOM_TRUST_BOOTLOADER)) {
> +		size_t l = strlen(command_line);
> +		char *rng_seed = strnstr(command_line, rng_seed_str, l);
> +
> +		if (rng_seed) {
> +			char *end;
> +
> +			rng_seed += strlen(rng_seed_str);
> +			l -= rng_seed - command_line;
> +			end = strnchr(rng_seed, l, ' ');
> +			if (end)
> +				l = end - rng_seed;
> +			credit_trusted_entropy(l);
> +		}
> +	}

This doesn't look right at all.  It calls credit_trusted_entropy(),
but it doesn't actually feed the contents of rng_seed where.  Why not
just call add_hwgeneterator_randomness() and drop adding this
credit_trusted_entropy(l)?

						- Ted