linux-hardening - Re: [PATCH v2] gcc-plugins: latent

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Date:   Tue, 5 Apr 2022 10:17:50 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, PaX Team <pageexec@...email.hu>
Subject: Re: [PATCH v2] gcc-plugins: latent_entropy: use /dev/urandom

On Tue, Apr 05, 2022 at 02:38:58PM +0200, Jason A. Donenfeld wrote:
> Hi Kees,
> 
> On 4/5/22, Kees Cook <keescook@...omium.org> wrote:
> > On Tue, Apr 05, 2022 at 12:47:14AM +0200, Jason A. Donenfeld wrote:
> >> On Mon, Apr 4, 2022 at 8:49 PM Kees Cook <keescook@...omium.org> wrote:
> >> > This mixes two changes: the pRNG change and the "use urandom if
> >> > non-deterministic" change. I think these should be split, so the pRNG
> >> > change can be explicitly justified.
> >>
> >> Alright, I'll split those. Or, more probably, just drop the xorshift
> >> thing. There's not actually a strong reason for preferring xorshift. I
> >> did it because it produces more uniformity and is faster to compute and
> >> all that. But none of that stuff actually matters here. It was just a
> >> sort of "well I'm at it..." thing.
> >
> > Well, it's nice to have and you already wrote it, so seems a waste to
> > just drop it. :)
> >
> >> > >  static struct plugin_info latent_entropy_plugin_info = {
> >> > > -     .version        = "201606141920vanilla",
> >> > > +     .version        = "202203311920vanilla",
> >> >
> >> > This doesn't really need to be versioned. We can change this to just
> >> > "vanilla", IMO.
> >>
> >> Okay. I suppose you want it to be in a different patch too, right? In
> >> which case I'll leave it out and maybe get to it later. (I suppose one
> >> probably needs to double check whether it's used for anything
> >> interesting like dwarf debug info or whatever, where maybe it's
> >> helpful?)
> >
> > Hm, I don't think it shows up anywhere, but you can just drop the hunk
> > that touch it. I can remove them all with a separate patch later.
> >
> 
> Okay. That's what I did here
> https://lore.kernel.org/lkml/20220404230709.124508-1-Jason@zx2c4.com/
> so awaiting your merge. (I still find all aspects of v2 more
> preferable for a variety of weak reasons in case you'd like to merge
> that instead, but v3 is available now.)

v3 uses a different check for the -f option, though? Isn't that
preferred over the v2 method?

Also, I did some quick benchmarking, and any difference in runtime is
completely lost in the noise, so that's good.

-- 
Kees Cook