kernel-hardening - Re: RANDSTRUCT structs need linux/compiler_types.h (Was: [nfsd4] potentially hardware breaking regression in 4.14-rc and 4.13.11)

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Message-ID: <CAGXu5j+gvH+X-XyqFbY+X0xtG2mQoL5bO7T2_QaeEyr3-Z5eLw@mail.gmail.com>
Date: Wed, 21 Feb 2018 14:52:28 -0800
From: Kees Cook <keescook@...omium.org>
To: "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
Cc: Patrick McLean <chutzpah@...too.org>, Linus Torvalds <torvalds@...ux-foundation.org>, 
	Emese Revfy <re.emese@...il.com>, Al Viro <viro@...iv.linux.org.uk>, 
	Bruce Fields <bfields@...hat.com>, "Darrick J. Wong" <darrick.wong@...cle.com>, 
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, 
	Linux NFS Mailing List <linux-nfs@...r.kernel.org>, Thorsten Leemhuis <regressions@...mhuis.info>, 
	"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: RANDSTRUCT structs need linux/compiler_types.h (Was: [nfsd4]
 potentially hardware breaking regression in 4.14-rc and 4.13.11)

On Wed, Feb 21, 2018 at 2:19 PM, Maciej S. Szmigiero
<mail@...iej.szmigiero.name> wrote:
> One can see that offsets used to access various members of struct path are
> different, and also that the original file from step 3 contains an object
> named "__randomize_layout".
>
> This is caused by a fact that the current version of nfs4xdr.c includes
> linux/fs_struct.h as the very first included header which then includes
> linux/path.h as the very first included header, which then defines
> struct path, but without including any files on its own.
>
> This results in __randomize_layout tag at the end of struct path
> definition being treated as a variable name (since linux/compiler-gcc.h
> that defines it as a type attribute has not been included yet).

Oh, well done! That would explain the code offset I was seeing when
the plugin on, but no-op, since the variable would still exist.

I'll play with Linus's suggestion and see what we get.

Thanks!

-Kees

-- 
Kees Cook
Pixel Security

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