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Date:   Mon, 23 Apr 2018 20:00:09 +0200
From:   Joerg Roedel <jroedel@suse.de>
To:     Kees Cook <keescook@google.com>
Cc:     Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>,
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        Linux-MM <linux-mm@kvack.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Juergen Gross <jgross@suse.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Borislav Petkov <bp@alien8.de>, Jiri Kosina <jkosina@suse.cz>,
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        Brian Gerst <brgerst@gmail.com>,
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        Eduardo Valentin <eduval@amazon.com>,
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        Waiman Long <llong@redhat.com>, Pavel Machek <pavel@ucw.cz>,
        "David H . Gutteridge" <dhgutteridge@sympatico.ca>
Subject: Re: [PATCH 27/37] x86/mm/pti: Keep permissions when cloning kernel
 text in pti_clone_kernel_text()
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On Mon, Apr 23, 2018 at 10:06:20AM -0700, Kees Cook wrote:
> Why are there R/W text mappings in this range? I find that to be
> unexpected. Shouldn't CONFIG_DEBUG_WX already complain if that were
> true?

It actually complains, I have seen that with the base-kernel too. I
guess this is because of the different mark_rodata_ro() and
mark_nxdata_nx() implementations between 32 and 64 bit. They actually
protect different regions, I think one reason is that some regions are
not hupe-page aligned on 32 bit and doing the right protections as on 64
bit would require to split the 2M mappings into 4k mappings.

But I havn't looked deeper into that and whether it can be unified and
fixed for 32 bit. It is probably out-of-scope for this patch-set.


Regards,

	Joerg