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

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Message-Id: <20200521120843.427b7ff33f8ed7f824eb07f9@linux-foundation.org>
Date:   Thu, 21 May 2020 12:08:43 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Steven Price <steven.price@....com>
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 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(?).

> 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.