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Date: Thu, 1 Oct 2015 21:41:21 +0200
From: Borislav Petkov <bp@alien8.de>
To: Kees Cook <keescook@chromium.org>
Cc: Stephen Smalley <sds@tycho.nsa.gov>, "x86@kernel.org" <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC][PATCH] x86/mm: warn on W+x mappings
Message-ID: <20151001194121.GC3764@pd.tnic>
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On Thu, Oct 01, 2015 at 12:24:25PM -0700, Kees Cook wrote:
> On Thu, Oct 1, 2015 at 9:28 AM, Stephen Smalley <sds@tycho.nsa.gov> wrote:
> > Warn on any residual W+x mappings if X86_PTDUMP is enabled.
> >
> > Sample dmesg output:
> > Checking for W+x mappings
> > 0xffffffff81755000-0xffffffff81800000         684K     RW                 GLB x  pte
> > Found W+x mappings.  Please fix.
> >
> > Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
> > ---
> > Not sure if this is the best place to put this check.
> > It must occur after free_init_pages() or it won't catch the
> > W+x case for the gap between __ex_table and rodata.
> 
> Yeah. Hmm. I want this test for sure, but I'd like to be able to do
> with without needing PTDUMP, since that puts a very sensitive file in
> debugfs. I wonder if we can reuse the same code, but only expose the
> page tables to userspace with PTDUMP?

So make it a debugging option like CONFIG_EFI_PGT_DUMP and let it dump
the pagetable in dmesg during boot, at the exact point you want it to.
Then one can grep dmesg for W+x bits or whatever else...

-- 
Regards/Gruss,
    Boris.

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