linux-kernel - Re: [PATCH] binfmt_elf: Move brk out of mmap when doing direct loader exec

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Message-ID: <CAGXu5jJsaKU1O7GQG0oEQfnMGSdRE-QEfd8c1Gn6YuPA66K-nQ@mail.gmail.com>
Date:   Mon, 22 Apr 2019 15:48:58 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Ali Saidi <alisaidi@...zon.com>,
        Michal Hocko <mhocko@...e.com>,
        Matthew Wilcox <willy@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jann Horn <jannh@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] binfmt_elf: Move brk out of mmap when doing direct loader exec

On Thu, Apr 18, 2019 at 7:57 AM Guenter Roeck <linux@...ck-us.net> wrote:
>
> On Mon, Apr 15, 2019 at 09:23:20PM -0700, Kees Cook wrote:
> > Commit eab09532d400 ("binfmt_elf: use ELF_ET_DYN_BASE only for PIE"),
> > made changes in the rare case when the ELF loader was directly invoked
> > (e.g to set a non-inheritable LD_LIBRARY_PATH, testing new versions of
> > the loader), by moving into the mmap region to avoid both ET_EXEC and PIE
> > binaries. This had the effect of also moving the brk region into mmap,
> > which could lead to the stack and brk being arbitrarily close to each
> > other. An unlucky process wouldn't get its requested stack size and stack
> > allocations could end up scribbling on the heap.
> >
>
> This patch results in crashes of my xtensa boot tests.
>
> Run /sbin/init as init process
> Kernel panic - not syncing: Attempted to kill init!  exitcode=0x0000000b

Thanks for finding this! I *think* the issue is that I needed to be
testing for CONFIG_ARCH_HAS_ELF_RANDOMIZATION, which xtensa lacks.
I'll get this fixed up and resent through -mm.

-- 
Kees Cook