linux-kernel - Re: [PATCH] task_struct: Only use anon struct under randstruct plugin

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Message-Id: <20180327160342.e2bc9a15afda5823c8daf4fb@linux-foundation.org>
Date:   Tue, 27 Mar 2018 16:03:42 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH] task_struct: Only use anon struct under randstruct
 plugin

On Tue, 27 Mar 2018 14:36:09 -0700 Kees Cook <keescook@...omium.org> wrote:

> The original intent for always adding the anonymous struct in task_struct
> was to make sure we had compiler coverage. However, this caused
> pathological padding of 40 bytes at the start of task_struct.

Why?  What caused this padding?  It happens in all configs?

> Instead,
> move the anonymous struct to being only used when struct layout
> randomization is enabled.

So the mysterious 40 byte bloat is still present in this case?

> Reported-by: Peter Zijlstra <peterz@...radead.org>
> Fixes: 29e48ce87f1e ("task_struct: Allow randomized")
> Cc: stable@...r.kernel.org

Why cc:stable?