linux-kernel - Re: [PATCH v2 2/5] arm64, mm: Move generic mmap layout functions to mm

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Date:   Tue, 9 Apr 2019 23:59:08 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Alexandre Ghiti <alex@...ti.fr>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Kees Cook <keescook@...omium.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Will Deacon <will.deacon@....com>,
        Russell King <linux@...linux.org.uk>,
        Ralf Baechle <ralf@...ux-mips.org>,
        linux-kernel@...r.kernel.org,
        Christoph Hellwig <hch@...radead.org>, linux-mm@...ck.org,
        Paul Burton <paul.burton@...s.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        James Hogan <jhogan@...nel.org>, linux-fsdevel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-mips@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Luis Chamberlain <mcgrof@...nel.org>
Subject: Re: [PATCH v2 2/5] arm64, mm: Move generic mmap layout functions to
 mm

On Thu, Apr 04, 2019 at 01:51:25AM -0400, Alexandre Ghiti wrote:
> - fix the case where stack randomization should not be taken into
>   account.

Hmm.  This sounds a bit vague.  It might be better if something
considered a fix is split out to a separate patch with a good
description.

> +config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
> +	bool
> +	help
> +	  This allows to use a set of generic functions to determine mmap base
> +	  address by giving priority to top-down scheme only if the process
> +	  is not in legacy mode (compat task, unlimited stack size or
> +	  sysctl_legacy_va_layout).

Given that this is an option that is just selected by other Kconfig
options the help text won't ever be shown.  I'd just move it into a
comment bove the definition.

> +#ifdef CONFIG_MMU
> +#ifdef CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT

I don't think we need the #ifdef CONFIG_MMU here,
CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT should only be selected
if the MMU is enabled to start with.

> +#ifdef CONFIG_ARCH_HAS_ELF_RANDOMIZE
> +unsigned long arch_mmap_rnd(void)

Now that a bunch of architectures use a version in common code
the arch_ prefix is a bit mislead.  Probably not worth changing
here, but some time in the future it could use a new name.