linux-kernel - Re: [PATCH] mm: optionally disable brk()

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Message-ID: <20201005092031.GS4555@dhcp22.suse.cz>
Date:   Mon, 5 Oct 2020 11:20:31 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Topi Miettinen <toiwoton@...il.com>, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: optionally disable brk()

On Mon 05-10-20 11:13:48, David Hildenbrand wrote:
> On 05.10.20 08:12, Michal Hocko wrote:
> > On Sat 03-10-20 00:44:09, Topi Miettinen wrote:
> >> On 2.10.2020 20.52, David Hildenbrand wrote:
> >>> On 02.10.20 19:19, Topi Miettinen wrote:
> >>>> The brk() system call allows to change data segment size (heap). This
> >>>> is mainly used by glibc for memory allocation, but it can use mmap()
> >>>> and that results in more randomized memory mappings since the heap is
> >>>> always located at fixed offset to program while mmap()ed memory is
> >>>> randomized.
> >>>
> >>> Want to take more Unix out of Linux?
> >>>
> >>> Honestly, why care about disabling? User space can happily use mmap() if
> >>> it prefers.
> >>
> >> brk() interface doesn't seem to be used much and glibc is happy to switch to
> >> mmap() if brk() fails, so why not allow disabling it optionally? If you
> >> don't care to disable, don't do it and this is even the default.
> > 
> > I do not think we want to have config per syscall, do we? 
> 
> I do wonder if grouping would be a better option then (finding a proper
> level of abstraction ...).

I have a vague recollection that project for the kernel tinification was
aiming that direction. No idea what is the current state or whether
somebody is pursuing it.

-- 
Michal Hocko
SUSE Labs