linux-kernel - Re: [PATCH RESEND] x86: consider effective protection attributes in W+X check

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Message-ID: <20180220083211.s5wr5r7ocpzzizgp@gmail.com>
Date:   Tue, 20 Feb 2018 09:32:11 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Jan Beulich <JBeulich@...e.com>
Cc:     mingo@...e.hu, tglx@...utronix.de,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
        hpa@...or.com
Subject: Re: [PATCH RESEND] x86: consider effective protection attributes in
 W+X check


* Jan Beulich <JBeulich@...e.com> wrote:

> >>> On 20.02.18 at 09:10, <mingo@...nel.org> wrote:
> > * Jan Beulich <JBeulich@...e.com> wrote:
> >> Using just the leaf page table entry flags would cause a false warning
> >> in case _PAGE_RW is clear or _PAGE_NX is set in a higher level entry.
> > 
> > Under what circumstances did you see false positive warnings?
> 
> As explained in the 2-patch series this was originally part of, there
> continues to be that W+X warning when running under Xen, as
> commit 2cc42bac1c ("x86-64/Xen: eliminate W+X mappings") has
> to make the necessary adjustment in L2 rather than L1 (the
> reason is explained there). I.e. _PAGE_RW is clear there in L1,
> but _PAGE_NX is set in L2.

This would make an excellent additional paragraph of the v2 changelog.

Thanks,

	Ingo