linux-kernel - Re: linux-next: build failure after merge of the origin tree

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Date:   Thu, 30 Jul 2020 11:47:22 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Emese Revfy <re.emese@...il.com>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Willy Tarreau <w@....eu>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: Re: linux-next: build failure after merge of the origin tree

On Thu, Jul 30, 2020 at 11:24:44AM -0700, Linus Torvalds wrote:
> On Wed, Jul 29, 2020 at 8:17 PM Kees Cook <keescook@...omium.org> wrote:
> >
> > I'll look into this more tomorrow. (But yes, __latent_entropy is
> > absolutely used for globals already, as you found, but this is the first
> > percpu it was applied to...)
> 
> Note that it was always per-cpu.
> 
> The only thing that changed was that it was declared static in
> lib/random.c vs being externally visible.

Yup, thanks. I realized that a bit after sending my email. :)

> Unrelated side note: I notice that the plugins could be simplified a
> bit now that we require gcc 4.9 or later. There's a fair amount of
> cruft for the earlier gcc versions.

Yup -- Masahiro keeps poking the build system, but I haven't cleaned up
the header file macros to keep up with the recent jumps. (It falls a bit
low on my TODO list since it's a bit of a mechanical cleanup. I'm open
to anyone that would like to send patches, though!)

> I'm not sure how seriously the gcc plugins are actually maintained (no
> offense) aside from just keeping them limping along. Does anybody
> actually use them in production? I thought google had mostly moved on
> to clang.

They're part of regular testing, and there is ongoing development
(e.g. see Alex Popov's recent series[1], which is in -next waiting for
the v5.9 merge window). I hear regularly from folks using randstruct,
stackleak, structleak, and latent_entropy. But yes, Google has moved
to Clang where we're using Clang's implementation of structleak
(auto-var-init) but there has been work to get randstruct ported (as
desired by at least one Android vendor), though it's currently stalled.

-Kees

[1] https://lore.kernel.org/lkml/20200624123330.83226-1-alex.popov@linux.com/

-- 
Kees Cook