linux-kernel - Re: [PATCH v2] x86: consider effective protection attributes in W+X check

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Date:   Wed, 21 Feb 2018 17:53:44 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Jan Beulich <JBeulich@...e.com>
Cc:     mingo@...e.hu, tglx@...utronix.de, hpa@...or.com,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] x86: consider effective protection attributes in W+X
 check


* 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.
> Hand through both the current entry's flags as well as the accumulated
> effective value (the latter as pgprotval_t instead of pgprot_t, as it's
> not an actual entry's value).
> 
> This in particular eliminates the false 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.
> 
> Signed-off-by: Jan Beulich <jbeulich@...e.com>
> Reviewed-by: Juergen Gross <jgross@...e.com>
> ---
> v2: Re-base onto tip tree. Add Xen related paragraph to description.
> ---
>  arch/x86/mm/dump_pagetables.c |   92 ++++++++++++++++++++++++++----------------
>  1 file changed, 57 insertions(+), 35 deletions(-)

There's a build failure with CONFIG_KASAN=y enabled:

 arch/x86/mm/dump_pagetables.c: In function ‘kasan_page_table’:
 arch/x86/mm/dump_pagetables.c:365:3: error: too few arguments to function ‘note_page’
 arch/x86/mm/dump_pagetables.c:238:13: note: declared here

Thanks,

	Ingo