linux-kernel - Re: [PATCH 2/3] random: rng-seed source is utf-8

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Date:   Tue, 18 Feb 2020 12:14:53 -0500
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Mark Salyzyn <salyzyn@...roid.com>
Cc:     Rob Herring <robh@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Android Kernel Team <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>,
        Steven Rostedt <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>,
        Jonathan Corbet <corbet@....net>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Juergen Gross <jgross@...e.com>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>
Subject: Re: [PATCH 2/3] random: rng-seed source is utf-8

On Tue, Feb 18, 2020 at 08:01:51AM -0800, Mark Salyzyn wrote:
> I am additionally concerned about add_bootloader_randomness() because it is
> possible for it to sleep because of add_hwgenerator_randomness() as once it
> hits the entropy threshold. As-is it can not be used inside start_kernel()
> because the sleep would result in a kernel panic, and I suspect its use
> inside early_init_dt_scan_chosen() for the commit "fdt: add support for
> rng-seed" might also be problematic since it is effectively called
> underneath start_kernel() is it not?
> 
> If add_bootloader_randomness was rewritten to call add_device_randomness()
> always, and when trusted also called the functionality of the new
> credit_trusted_entropy_bits (no longer needing to be exported if so), then
> the function could be used in both start_kernel() and
> early_init_dt_scan_chosen().

That's a good point, and it's a bug in add_bootloader_randomness().
That should be easily fixed by simply having it call mix_pool_bytes()
and credit_entropy_bits() directly.  I'll create a patch...

    			  	     	  	   - Ted