linux-kernel - Re: [PATCH] arm: don't allow CONFIG_DEBUG_SET_MODULE_RONX if CONFIG_JUMP

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Date:	Tue, 01 Apr 2014 11:03:35 -0700
From:	Laura Abbott <lauraa@...eaurora.org>
To:	Alexander Holler <holler@...oftware.de>,
	linux-arm-kernel@...ts.infradead.org
CC:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	linux-kernel@...r.kernel.org,
	Russell King <linux@....linux.org.uk>,
	Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] arm: don't allow CONFIG_DEBUG_SET_MODULE_RONX if CONFIG_JUMP_LABEL
 is enabled

On 4/1/2014 3:04 AM, Alexander Holler wrote:
> CONFIG_DEBUG_SET_MODULE_RONX sounds like a nice security feature, but
> things might fail late (and unexpected) if module code is set to read-only
> while CONFIG_JUMP_LABEL is enabled (e.g. modprobe bridge).
> 
> Avoid this.
> 
> Signed-off-by: Alexander Holler <holler@...oftware.de>
> ---
>  arch/arm/Kconfig.debug | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
> index 0531da8..6627b9e 100644
> --- a/arch/arm/Kconfig.debug
> +++ b/arch/arm/Kconfig.debug
> @@ -1197,7 +1197,7 @@ config PID_IN_CONTEXTIDR
>  
>  config DEBUG_SET_MODULE_RONX
>  	bool "Set loadable kernel module data as NX and text as RO"
> -	depends on MODULES
> +	depends on MODULES && !JUMP_LABEL
>  	---help---
>  	  This option helps catch unintended modifications to loadable
>  	  kernel module's text and read-only data. It also prevents execution
> 

Kees Cook has something similar[1] for not-module space as well, we probably want
this there as well. A shame we keep finding reasons these features will be turned
off. Looks good to me otherwise. 

Laura

[1]http://lists.infradead.org/pipermail/linux-arm-kernel/2014-February/232644.html

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