linux-kernel - Re: [PATCH -mm 1/3] proc: randomize "struct pde

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Message-ID: <CAGXu5jJ20D=Eq0uVgd=7mBeg6Qseob+6G9YktLW02-CEyLeYQA@mail.gmail.com>
Date:   Thu, 15 Feb 2018 17:03:25 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -mm 1/3] proc: randomize "struct pde_opener"

On Thu, Feb 15, 2018 at 4:13 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
> Guess what happens to cache footprint of dcache lookups if the bunch in the
> beginning gets spread over the entire thing?  Right...  And that's besides the
> outright miscompiles.

Mentioned in private communication, but just for posterity:
GCC_PLUGIN_RANDSTRUCT_PERFORMANCE exists specifically to address those
kinds of performance concerns.

As to removing the markings: please don't. Instead, you'd mentioned
wanting to add a TAINT flag for this, and I think that sounds entirely
reasonable. We have TAINT flags for considerably less insane things.
:) I can send that patch.

-Kees

-- 
Kees Cook
Pixel Security