linux-kernel - Re: [PATCH v3 04/11] arm64, mm: Move generic mmap layout functions to mm

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Date:   Mon, 22 Apr 2019 21:55:56 +0200
From:   Christoph Hellwig <hch@....de>
To:     Kees Cook <keescook@...omium.org>
Cc:     Alex Ghiti <alex@...ti.fr>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        Palmer Dabbelt <palmer@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Luis Chamberlain <mcgrof@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-mips@...r.kernel.org, linux-riscv@...ts.infradead.org,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH v3 04/11] arm64, mm: Move generic mmap layout functions
 to mm

On Thu, Apr 18, 2019 at 09:19:18AM -0500, Kees Cook wrote:
> On Thu, Apr 18, 2019 at 12:55 AM Alex Ghiti <alex@...ti.fr> wrote:
> > Regarding the help text, I agree that it does not seem to be frequent to
> > place
> > comment above config like that, I'll let Christoph and you decide what's
> > best. And I'll
> > add the possibility for the arch to define its own STACK_RND_MASK.
> 
> Yeah, I think it's very helpful to spell out the requirements for new
> architectures with these kinds of features in the help text (see
> SECCOMP_FILTER for example).

Spelling out the requirements sounds useful.  Abusing the help text
for an option for which no help text can be displayed it pointless.
Just make it a comment as Alex did in this patch, which makes whole
lot more sense.

> > Actually, I had to add those ifdefs for mmap_rnd_compat_bits, not
> > is_compat_task.
> 
> Oh! In that case, use CONFIG_HAVE_ARCH_MMAP_RND_BITS. :) Actually,
> what would be maybe cleaner would be to add mmap_rnd_bits_min/max
> consts set to 0 for the non-CONFIG_HAVE_ARCH_MMAP_RND_BITS case at the
> top of mm/mmap.c.

Lets do that in a second step.  The current series is already big
enough and a major improvement, even if there is much more to clean
up in this area still left.