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Reply-To: crecklin@redhat.com
Subject: Re: [PATCH] add param that allows bootline control of hardened
 usercopy
To:     Kees Cook <keescook@chromium.org>
Cc:     Laura Abbott <labbott@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>
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From:   Christoph von Recklinghausen <crecklin@redhat.com>
Organization: Red Hat
Message-ID: <53edba5a-1652-d1c2-12c9-7f3cda746f5f@redhat.com>
Date:   Mon, 25 Jun 2018 19:17:16 -0400
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On 06/25/2018 06:35 PM, Kees Cook wrote:
> On Mon, Jun 25, 2018 at 3:29 PM, Christoph von Recklinghausen
> <crecklin@redhat.com> wrote:
>> I have a small set of customers that want CONFIG_HARDENED_USERCOPY
>> enabled, and a large number of customers who would be impacted by its
>> default behavior (before my change).  The desire was to have the smaller
>> number of users need to change their boot lines to get the behavior they
>> wanted. Adding CONFIG_HUC_DEFAULT_OFF was an attempt to preserve the
>> default behavior of existing users of CONFIG_HARDENED_USERCOPY (default
>> enabled) and allowing that to coexist with the desires of the greater
>> number of my customers (default disabled).
>>
>> If folks think that it's better to have it enabled by default and the
>> command line option to turn it off I can do that (it is simpler). Does
>> anyone else have opinions one way or the other?
> I would prefer to isolate the actual problem case, and fix it if
> possible. (i.e. try to make the copy fixed-length, etc) Barring that,
> yes, a kernel command line to disable the protection would be okay.
>
> Note that the test needs to be inside __check_object_size() otherwise
> the inline optimization with __builtin_constant_p() gets broken and
> makes everyone slower. :)
>
> -Kees
>
Thanks Kees,

I'll make that change and retest.

Chris