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

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Message-Id: <20200521152308.33096-1-steven.price@arm.com>
Date:   Thu, 21 May 2020 16:23:06 +0100
From:   Steven Price <steven.price@....com>
To:     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,
        Jan Beulich <jbeulich@...e.com>
Cc:     Steven Price <steven.price@....com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: [PATCH 0/2] Fix W+X debug feature on x86

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'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.

[1] https://lore.kernel.org/lkml/d573dc7e-e742-84de-473d-f971142fa319@suse.com/
[2] 2ae27137b2db ("x86: mm: convert dump_pagetables to use walk_page_range")

Steven Price (2):
  x86: mm: ptdump: Calculate effective permissions correctly
  mm: ptdump: Expand type of 'val' in note_page()

 arch/arm64/mm/dump.c          |  2 +-
 arch/x86/mm/dump_pagetables.c | 33 ++++++++++++++++++++-------------
 include/linux/ptdump.h        |  3 ++-
 mm/ptdump.c                   | 17 ++++++++++++++++-
 4 files changed, 39 insertions(+), 16 deletions(-)

-- 
2.20.1