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Date: Mon, 23 Apr 2018 20:00:09 +0200
From: Joerg Roedel <jroedel@suse.de>
Subject: Re: [PATCH 27/37] x86/mm/pti: Keep permissions when cloning kernel
 text in pti_clone_kernel_text()
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To: Kees Cook <keescook@google.com>
Cc: Joerg Roedel <joro@8bytes.org>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>, "H . Peter Anvin" <hpa@zytor.com>, X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>, 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>, Boris Ostrovsky <boris.ostrovsky@oracle.com>, Brian Gerst <brgerst@gmail.com>, David Laight <David.Laight@aculab.com>, Denys Vlasenko <dvlasenk@redhat.com>, Eduardo Valentin <eduval@amazon.com>, Greg KH <gregkh@linuxfoundation.org>, Will Deacon <will.deacon@arm.com>, Anthony Liguori <aliguori@amazon.com>, Daniel Gruss <daniel.gruss@iaik.tugraz.at>, Hugh Dickins <hughd@google.com>, Andrea Arcangeli <aarcange@redhat.com>, Waiman Long <llong@redhat.com>, Pavel Machek <pavel@ucw.cz>, "David H . Gutteridge" <dhgutteridge@sympatico.ca>

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