linux-kernel - Re: [PATCH] Consolidate CONFIG_DEBUG_STRICT_USER_COPY

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Date:	Wed, 27 Feb 2013 20:32:20 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>, linux-parisc@...r.kernel.org,
	linux-s390@...r.kernel.org,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Helge Deller <deller@....de>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Chris Metcalf <cmetcalf@...era.com>
Subject: Re: [PATCH] Consolidate CONFIG_DEBUG_STRICT_USER_COPY_CHECK

On Wednesday 27 February 2013, Stephen Boyd wrote:
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 28be08c..ae80518 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1292,6 +1292,24 @@ config LATENCYTOP
>  	  Enable this option if you want to use the LatencyTOP tool
>  	  to find out which userspace is blocking on what kernel operations.
>  
> +config ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS
> +	bool
> +
> +config DEBUG_STRICT_USER_COPY_CHECKS
> +	bool "Strict user copy size checks"
> +	depends on ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS
> +	depends on DEBUG_KERNEL && !TRACE_BRANCH_PROFILING
> +	help
> +	  Enabling this option turns a certain set of sanity checks for user
> +	  copy operations into compile time failures.
> +
> +	  The copy_from_user() etc checks are there to help test if there
> +	  are sufficient security checks on the length argument of
> +	  the copy operation, by having gcc prove that the argument is
> +	  within bounds.
> +
> +	  If unsure, say N.
> +

Is there actually any architecture dependency left after this?
I wonder if we actually need the ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS
symbol, or could just show the DEBUG_STRICT_USER_COPY_CHECKS option
on all architectures.

It's fine to do your patch as a first step though, which would not
change the behavior.

> diff --git a/lib/Makefile b/lib/Makefile
> index 32f4455..59fabd0 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -15,6 +15,7 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
>  	 is_single_threaded.o plist.o decompress.o kobject_uevent.o \
>  	 earlycpio.o percpu-refcount.o
>  
> +lib-$(CONFIG_ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS) += usercopy.o
>  lib-$(CONFIG_MMU) += ioremap.o
>  lib-$(CONFIG_SMP) += cpumask.o
>

I think this should instead be

+lib-$(DEBUG_STRICT_USER_COPY_CHECKS) += usercopy.o

No point building that file if we are not using it.

Other than that, 

Acked-by: Arnd Bergmann <arnd@...db.de>
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