linux-kernel - Re: [kernel-hardening] [RFC 0/4] make call

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Message-ID: <CAHmME9pq=1hZirN6uwM5Tgrp5iG5mqmXw37gQYxFzcJ4Kkj9dQ@mail.gmail.com>
Date:   Wed, 14 Dec 2016 22:28:18 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        kernel-hardening@...ts.openwall.com
Subject: Re: [kernel-hardening] [RFC 0/4] make call_usermodehelper a bit more "safe"

Hi Greg,

On Wed, Dec 14, 2016 at 7:50 PM, Greg KH <gregkh@...uxfoundation.org> wrote:
> So, anyone have any better ideas?  Is this approach worth it?  Or should
> we just go down the "whitelist" path?

I think your approach is generally better than the whitelist path. But
maybe there's yet a third approach that involves futzing with page
permissions at runtime. I think grsec does something similar with
read_mostly function pointer structs. Namely, they make them read-only
const, and then temporarily twiddle the page permissions if it needs
to be changed while disabling preemption. There could be a particular
class of data that needs to be "opened" and "closed" in order to
modify. Seems like these strings would be a good use of that.

Jason