linux-kernel - Re: [PATCH] Make taint bit reliable

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Date:	Tue, 2 Sep 2008 17:42:46 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Make taint bit reliable

On Mon, 1 Sep 2008 18:46:32 +0200
Andi Kleen <andi@...stfloor.org> wrote:

> Make taint bit reliable
> 
> It's somewhat unlikely that it happens, but right now a race window 
> between interrupts or machine checks or oopses could corrupt the tainted 
> bitmap because it is modified in a non atomic fashion.
> 
> Convert the taint variable to an unsigned long and use only atomic bit
> operations on it.
> 
> Unfortunately this means the intvec sysctl functions cannot be used on 
> it anymore.
> 
> It turned out the taint sysctl handler could actually be simplified
> a bit (since it only increases capabilities) so this patch actually
> removes code.
> 
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> 
> ---
>  include/linux/kernel.h |    2 -
>  kernel/panic.c         |    5 ++-
>  kernel/sysctl.c        |   67 +++++++++++++++++++++----------------------------
>  3 files changed, 33 insertions(+), 41 deletions(-)

You missed one:

./arch/x86/kernel/smpboot.c:                    tainted &= ~TAINT_UNSAFE_SMP;


To prevent reoccurrences we could/should rename `tainted' to something else.

Also, it would end up with a beter result if we were to change 

- #define TAINT_PROPRIETARY_MODULE        (1<<0)
- #define TAINT_FORCED_MODULE             (1<<1)
...
+ #define TAINT_PROPRIETARY_MODULE        0
+ #define TAINT_FORCED_MODULE             1
...


and remove that ungainly log2() you had to add, and just prevent all
open-coded access to the 'tainted' global.  ie: add `int get_taint(void)'?

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