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Date: Tue, 27 Sep 2016 20:55:44 -0600
From: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Al Viro <viro@zeniv.linux.org.uk>, linuxppc-dev@lists.ozlabs.org,
 Andrew Morton <akpm@linux-foundation.org>,
 Denys Vlasenko <dvlasenk@redhat.com>,
 Benjamin Herrenschmidt <benh@kernel.crashing.org>,
 Paul Mackerras <paulus@samba.org>,
 "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
 Kees Cook <keescook@chromium.org>, Oleg Nesterov <oleg@redhat.com>,
 Florian Weimer <fweimer@redhat.com>, linux-mm@kvack.org,
 linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5] powerpc: Do not make the entire heap executable
Message-ID: <20160928025544.GA24199@obsidianresearch.com>
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On Wed, Sep 28, 2016 at 11:42:11AM +1000, Michael Ellerman wrote:

> But this is not really a powerpc patch, and I'm not an ELF expert. So
> I'm not comfortable merging it via the powerpc tree. It doesn't look
> like we really have a maintainer for binfmt_elf.c, so I'm not sure who
> should be acking that part.

Thanks a bunch for looking at this Michael.

> I've added Al Viro to Cc, he maintains fs/ and might be interested.

> I've also added Andrew Morton who might be happy to put this in his
> tree, and see if anyone complains?

For those added to the CC, I would re-state my original commit message
more clearly.

My research showed that the ELF loader bug fixed in this patch is the
root cause bug fix required to implement this hunk:

> > -#define VM_DATA_DEFAULT_FLAGS32	(VM_READ | VM_WRITE | VM_EXEC | \
> > +#define VM_DATA_DEFAULT_FLAGS32 \
> > +	(((current->personality & READ_IMPLIES_EXEC) ? VM_EXEC : 0) | \
> > +				 VM_READ | VM_WRITE | \
> >  				 VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC)

Eg that 32 bit powerpc currently unconditionally injects writable,
executable pages into a user space process.

This critically undermines all the W^X security work that has been
done in the tool chain and user space by the PPC community.

I would encourage people to view this as an important security patch
for 32 bit powerpc environments.

Regards,
Jason