linux-kernel - Re: [PATCH 1/2] x86: mm: ptdump: Calculate effective permissions correctly

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Date:   Wed, 27 May 2020 17:15:17 +0200
From:   Jan Beulich <jbeulich@...e.com>
To:     Steven Price <steven.price@....com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 1/2] x86: mm: ptdump: Calculate effective permissions
 correctly

On 21.05.2020 17:23, Steven Price wrote:
> By switching the x86 page table dump code to use the generic code the
> effective permissions are no longer calculated correctly because the
> note_page() function is only called for *leaf* entries. To calculate the
> actual effective permissions it is necessary to observe the full
> hierarchy of the page tree.
> 
> Introduce a new callback for ptdump which is called for every entry and
> can therefore update the prot_levels array correctly. note_page() can
> then simply access the appropriate element in the array.
> 
> Reported-by: Jan Beulich <jbeulich@...e.com>
> Fixes: 2ae27137b2db ("x86: mm: convert dump_pagetables to use walk_page_range")
> Signed-off-by: Steven Price <steven.price@....com>

This (with the later correction) and the 2nd patch
Tested-by: Jan Beulich <jbeulich@...e.com>

It allowed me to go and finally find why under Xen there was still
a single W+X mapping left - another bug, another patch.

Thanks, Jan