linux-kernel - Re: [PATCH] sgi-xp: use designated initializers

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Date:   Tue, 3 Jan 2017 15:19:26 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Robin Holt <robinmholt@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, Cliff Whickman <cpw@....com>
Subject: Re: [PATCH] sgi-xp: use designated initializers

On Wed, Dec 21, 2016 at 8:24 AM, Robin Holt <robinmholt@...il.com> wrote:
> On Fri, Dec 16, 2016 at 7:01 PM, Kees Cook <keescook@...omium.org> wrote:
>> Prepare to mark sensitive kernel structures for randomization by making
>> sure they're using designated initializers. These were identified during
>> allyesconfig builds of x86, arm, and arm64, with most initializer fixes
>> extracted from grsecurity.
>
> I guess I don't understand the context enough here to give you a
> Signed-off-by.  Can you give us more background on this randomization?

Sure thing! The randomization is on the order of function pointers in
all-pointer structures (like struct xpc_interface). As long as the
memory containing the structure isn't shared externally, this
randomization should have no operational effect. The reason explicit
no-op functions were added was to avoid ugly casts, etc.

> From what I see in the code here, I can see you are providing
> equivalent functionality and I would give it a signed-off-by, but I am
> not sure this randomization of which you speak is not going to cause
> problems for XP, XPC, XPNET, and XPMEM (out of tree GPL kernel
> module).

Ah, hm, does this module share the structure without being built
against the kernel? (If built with the kernel, the randomization
plugin will keep things in the right order.)

-Kees

-- 
Kees Cook
Nexus Security