linux-kernel - Re: [PATCH] Kbuild: disable FORTIFY

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Message-ID: <202005051617.F9B32B5526@keescook>
Date:   Tue, 5 May 2020 16:19:02 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Arnd Bergmann <arnd@...db.de>, George Burgess <gbiv@...gle.com>
Subject: Re: [PATCH] Kbuild: disable FORTIFY_SOURCE on clang-10

On Tue, May 05, 2020 at 04:37:38PM -0600, Jason A. Donenfeld wrote:
> On Tue, May 5, 2020 at 4:25 PM Nathan Chancellor
> <natechancellor@...il.com> wrote:
> > I believe these issues are one in the same. I did a reverse bisect with
> > Arnd's test case and converged on George's first patch:
> >
> > https://github.com/llvm/llvm-project/commit/2dd17ff08165e6118e70f00e22b2c36d2d4e0a9a
> >
> > I think that in lieu of this patch, we should have that patch and its
> > follow-up fix merged into 10.0.1.
> 
> If this is fixed in 10.0.1, do we even need to patch the kernel at
> all? Or can we just leave it be, considering most organizations using
> clang know what they're getting into? I'd personally prefer the
> latter, so that we don't clutter things.

I agree: I'd rather this was fixed in 10.0.1 (but if we do want a
kernel-side work-around for 10.0.0, I would suggest doing the version
check in the Kconfig for FORTIFY_SOURCE instead of in the Makefile,
as that's where these things are supposed to live these days).

(Though as was mentioned, it's likely that FORTIFY_SOURCE isn't working
_at all_ under Clang, so I may still send a patch to depend on !clang
just to avoid surprises until it's fixed, but I haven't had time to
chase down a solution yet.)

-- 
Kees Cook