linux-kernel - Re: [PATCH 0/2] Fix W+X debug feature on x86

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Date:   Fri, 22 May 2020 13:50:28 +0100
From:   Steven Price <steven.price@....com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     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,
        Jan Beulich <jbeulich@...e.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 0/2] Fix W+X debug feature on x86

On 21/05/2020 20:08, Andrew Morton wrote:
> On Thu, 21 May 2020 16:23:06 +0100 Steven Price <steven.price@....com> wrote:
> 
>> Jan alert me[1] that the W+X detection debug feature was broken in x86
>> by my change[2] to switch x86 to use the generic ptdump infrastructure.
>>
>> Fundamentally the approach of trying to move the calculation of
>> effective permissions into note_page() was broken because note_page() is
>> only called for 'leaf' entries and the effective permissions are passed
>> down via the internal nodes of the page tree. The solution I've taken
>> here is to create a new (optional) callback which is called for all
>> nodes of the page tree and therefore can calculate the effective
>> permissions.
>>
>> Secondly on some configurations (32 bit with PAE) "unsigned long" is not
>> large enough to store the table entries. The fix here is simple - let's
>> just use a u64.
> 
> I assumed that a cc:stable was appropriate on both of these(?).

Yes thanks.

>> I'd welcome testing (and other comments), especially if you have a
>> configuration which previously triggered W+X warnings as I don't have
>> such a setup.
> 
> I'll wait a while for such testing.  If nothing happens then I guess we
> merge it up and see what then happens.
> 

Thanks,

Steve