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

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Date:   Wed, 10 Apr 2019 09:32:28 +0200
From:   Alexandre Ghiti <alex@...ti.fr>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     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, 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,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mips@...r.kernel.org, linux-riscv@...ts.infradead.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 04/10/2019 08:59 AM, Christoph Hellwig wrote:
> 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.

Ok, I will move this fix in another patch.

>
>> +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.

Oh yes, it does not appear, thanks, I'll move it above 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.

Ok, thanks.

>> +#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.

Ok I'll keep it in mind for later,

Thanks for your time,

Alex