linux-kernel - Re: [PATCH] hardening: add PROT_FINAL prot flag to mmap/mprotect

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Date:	Tue, 2 Oct 2012 17:43:20 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Kees Cook <keescook@...omium.org>,
	Ard Biesheuvel <ard.biesheuvel@...il.com>,
	linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
	Ingo Molnar <mingo@...nel.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	James Morris <jmorris@...ei.org>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	linux-mm@...ck.org
Subject: Re: [PATCH] hardening: add PROT_FINAL prot flag to mmap/mprotect

On Tue, 2 Oct 2012, Andrew Morton wrote:
> On Tue, 2 Oct 2012 15:10:56 -0700
> Kees Cook <keescook@...omium.org> wrote:
> 
> > >> Has there been any more progress on this patch over-all?
> > >
> > > No progress.
> > 
> > Al, Andrew, anyone? Thoughts on this?
> > (First email is https://lkml.org/lkml/2012/8/14/448)
> 
> Wasn't cc'ed, missed it.
> 
> The patch looks straightforward enough.  Have the maintainers of the
> runtime linker (I guess that's glibc) provided any feedback on the
> proposal?

It looks reasonable to me too.  I checked through VM_MAYflag handling
and don't expect surprises (a few places already turn off VM_MAYWRITE
in much the same way that this does, I hadn't realized).

I'm disappointed to find that our mmap() is lax about checking its
PROT and MAP args, so old kernels will accept PROT_FINAL but do
nothing with it.  Luckily mprotect() is stricter, so that can be
used to check for whether it's supported.

The patch does need to be slightly extended though: alpha, mips,
parisc and xtensa have their own include/asm/mman.h, which does
not include asm-generic/mman-common.h at all.

Hugh
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