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List:       kernel-hardening
Subject:    Re: [kernel-hardening] Re: [PATCH] lkdtm: Add tests for LIST_POISON and ZERO_SIZE_PTR
From:       Michael Ellerman <mpe () ellerman ! id ! au>
Date:       2016-11-18 2:37:59
Message-ID: 871sy9ikc8.fsf () concordia ! ellerman ! id ! au
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Kees Cook <keescook@chromium.org> writes:

> On Thu, Nov 17, 2016 at 2:53 AM, Michael Ellerman <mpe@ellerman.id.au> wrote:
> > kbuild test robot <lkp@intel.com> writes:
> > > [auto build test ERROR on char-misc/char-misc-testing]
> > > [also build test ERROR on v4.9-rc5]
> > > [cannot apply to next-20161115]
> > > [if your patch is applied to the wrong git tree, please drop us a note to help \
> > > improve the system] 
> > > url:    https://github.com/0day-ci/linux/commits/Michael-Ellerman/lkdtm-Add-tests-for-LIST_POISON-and-ZERO_SIZE_PTR/20161115-235441
> > >                 
> > > config: i386-randconfig-i0-201646 (attached as .config)
> > > compiler: gcc-4.8 (Debian 4.8.4-1) 4.8.4
> > > reproduce:
> > > # save the attached .config to linux build tree
> > > make ARCH=i386
> > > 
> > > All errors (new ones prefixed by >>):
> > > 
> > > > > ERROR: "mmap_min_addr" [drivers/misc/lkdtm.ko] undefined!
> > 
> > I couldn't see what was causing this, but of course it's just that
> > mmap_min_addr is not exported, and in that config LKDTM is a module.
> > 
> > I always build it in which is why I didn't notice.
> > 
> > I'm not sure we want to EXPORT_SYMBOL mmap_min_addr just for this test
> > do we? I could change the test to use mmap_min_addr if LKDTM is
> > built-in, and otherwise just map at zero. Dunno.
> 
> Because of lkdtm's moduleness, I've had to put a lot of weird stuff
> into EXPORT_SYMBOL_GPL(). mmap_min_addr is more sensitive than most,
> though. How about just hard-coding it as 64k instead of using
> mmap_min_addr?

We can just use CONFIG_DEFAULT_MMAP_MIN_ADDR, which should work unless
someone's actually changed the value at runtime. Will test.

I'd rather that than 64K hard-coded, as I'm thinking of increasing the
minimum on ppc64.

cheers


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