From mboxrd@z Thu Jan  1 00:00:00 1970
From: Al Viro <viro@ZenIV.linux.org.uk>
Subject: Re: [kernel-hardening] Re: [PATCH v9 1/4] syscalls: Verify address
 limit before returning to user-mode
Date: Fri, 12 May 2017 09:16:58 +0100
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On Fri, May 12, 2017 at 01:11:26AM -0700, Christoph Hellwig wrote:

> But it won't help against exploits modifying addr_limit manually.

Or the ones setting current->cred to that of init.  Your point being?