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

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Message-ID: <9aafccf1-0995-bea5-c814-c8cd9d719d12@arm.com>
Date:   Wed, 27 May 2020 16:55:26 +0100
From:   Steven Price <steven.price@....com>
To:     Jan Beulich <jbeulich@...e.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 27/05/2020 16:15, Jan Beulich wrote:
> 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
> 

Thanks for testing (and sorry for breaking it in the first place)!

Steve