linux-kernel - Re: [PATCH v7 13/14] module: Do not set nx for module memory before freeing

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Message-ID: <7B410C6F-A811-41DB-ADCE-4E4BF07CA96A@vmware.com>
Date:   Thu, 6 Dec 2018 18:56:14 +0000
From:   Nadav Amit <namit@...are.com>
To:     Andy Lutomirski <luto@...nel.org>
CC:     Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "linux_dti@...oud.com" <linux_dti@...oud.com>,
        linux-integrity <linux-integrity@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH v7 13/14] module: Do not set nx for module memory before
 freeing

> On Dec 6, 2018, at 10:52 AM, Andy Lutomirski <luto@...nel.org> wrote:
> 
> On Wed, Dec 5, 2018 at 12:52 AM Nadav Amit <namit@...are.com> wrote:
>> When module memory is about to be freed, there is no apparent reason to
>> make it (and its data) executable, but that's exactly what is done
>> today. This is not efficient and not secure.
>> 
>> There are various theories why it was done, but none of them seem as
>> something that really require it today. nios2 uses kmalloc for module
>> memory, but anyhow it does not change the PTEs of the module memory.  In
>> x86, changing vmalloc'd memory mappings also modifies the direct mapping
>> alias, but the NX-bit is not modified in such way.
>> 
>> So let's remove it. Andy suggested that the changes of the PTEs can be
>> avoided (excluding the direct-mapping alias), which is true. However,
>> in x86 it requires some cleanup of the contiguous page allocator, which
>> is outside of the scope of this patch-set.
> 
> 
> I'm okay with this, but I'd like to see Rick's stuff get rebased on
> top of it and clean it up for real.

Sorry for my laziness. It just seems that every small thing I touch in
regard to W^X or text_poke() is broken, and I need to finish some other
“chores” first.