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From:   Kees Cook <keescook@chromium.org>
Date:   Mon, 12 Feb 2018 17:25:25 -0800
Message-ID: <CAGXu5j++igQD4tMh0J8nZ9jNji5mU16C7OygFJ5Td+Bq-KSMgw@mail.gmail.com>
Subject: Re: [kernel-hardening] [PATCH 4/6] Protectable Memory
To:     Laura Abbott <labbott@redhat.com>
Cc:     Igor Stoppa <igor.stoppa@huawei.com>,
        Boris Lukashev <blukashev@sempervictus.com>,
        Christopher Lameter <cl@linux.com>,
        Matthew Wilcox <willy@infradead.org>,
        Jann Horn <jannh@google.com>,
        Jerome Glisse <jglisse@redhat.com>,
        Michal Hocko <mhocko@kernel.org>,
        Christoph Hellwig <hch@infradead.org>,
        linux-security-module <linux-security-module@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        kernel list <linux-kernel@vger.kernel.org>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>
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On Mon, Feb 12, 2018 at 4:40 PM, Laura Abbott <labbott@redhat.com> wrote:
> On 02/12/2018 03:27 PM, Kees Cook wrote:
>>
>> On Sun, Feb 4, 2018 at 7:05 AM, Igor Stoppa <igor.stoppa@huawei.com>
>> wrote:
>>>
>>> On 04/02/18 00:29, Boris Lukashev wrote:
>>>>
>>>> On Sat, Feb 3, 2018 at 3:32 PM, Igor Stoppa <igor.stoppa@huawei.com>
>>>> wrote:
>>>
>>>
>>> [...]
>>>
>>>>> What you are suggesting, if I have understood it correctly, is that,
>>>>> when the pool is protected, the addresses already given out, will
>>>>> become
>>>>> traps that get resolved through a lookup table that is built based on
>>>>> the content of each allocation.
>>>>>
>>>>> That seems to generate a lot of overhead, not to mention the fact that
>>>>> it might not play very well with the MMU.
>>>>
>>>>
>>>> That is effectively what i'm suggesting - as a form of protection for
>>>> consumers against direct reads of data which may have been corrupted
>>>> by some irrelevant means. In the context of pmalloc, it would probably
>>>> be a separate type of ro+verified pool
>>>
>>> ok, that seems more like an extension though.
>>>
>>> ATM I am having problems gaining traction to get even the basic merged
>>> :-)
>>>
>>> I would consider this as a possibility for future work, unless it is
>>> said that it's necessary for pmalloc to be accepted ...
>>
>>
>> I would agree: let's get basic functionality in first. Both
>> verification and the physmap part can be done separately, IMO.
>
>
> Skipping over physmap leaves a pretty big area of exposure that could
> be difficult to solve later. I appreciate this might block basic
> functionality but I don't think we should just gloss over it without
> at least some idea of what we would do.

What's our exposure on physmap for other regions? e.g. things that are
executable, or made read-only later (like __ro_after_init)?

-Kees

-- 
Kees Cook
Pixel Security