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

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Message-ID: <1B1C066C-04B2-4DD0-A28B-71BA7CDDD658@vmware.com>
Date:   Thu, 6 Dec 2018 20:29:37 +0000
From:   Nadav Amit <namit@...are.com>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
CC:     "luto@...nel.org" <luto@...nel.org>,
        "jeyu@...nel.org" <jeyu@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "linux_dti@...oud.com" <linux_dti@...oud.com>,
        "will.deacon@....com" <will.deacon@....com>,
        "bp@...en8.de" <bp@...en8.de>
Subject: Re: [PATCH v7 13/14] module: Do not set nx for module memory before
 freeing

> On Dec 6, 2018, at 12:21 PM, Edgecombe, Rick P <rick.p.edgecombe@...el.com> wrote:
> 
> On Thu, 2018-12-06 at 10:52 -0800, Andy Lutomirski 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.
> 
> Nadav,
> 
> Hmm, since you are trying to move things forward and not close all cases in one
> swoop, would it make sense to split the modules W^X mission from this patchset?

That’s what I tried to “hint”. Tglx asked for the module stuff in one of the
previous versions.