linux-kernel - Re: [PATCH 2/2] security: Change name of CONFIG_DEBUG_SET_MODULE

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Date:   Thu, 19 Jan 2017 11:11:18 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Laura Abbott <labbott@...hat.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Jason Wessel <jason.wessel@...driver.com>,
        Jonathan Corbet <corbet@....net>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        "James E.J. Bottomley" <jejb@...isc-linux.org>,
        Helge Deller <deller@....de>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Rob Herring <robh@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Jessica Yu <jeyu@...hat.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-parisc@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-pm@...r.kernel.org, kernel-hardening@...ts.openwall.com,
        "AKASHI, Takahiro" <takahiro.akashi@...aro.org>
Subject: Re: [PATCH 2/2] security: Change name of CONFIG_DEBUG_SET_MODULE_RONX

Hi,

On Wed, Jan 18, 2017 at 05:29:06PM -0800, Laura Abbott wrote:
> 
> Despite the word 'debug' in CONFIG_DEBUG_SET_MODULE_RONX, this kernel
> option provides key security features that are to be expected on a
> modern system. Change the name to CONFIG_HARDENED_MODULE_MAPPINGS which
> more accurately describes what this option is intended to do.

This looks good; my naming comments from the DEBUG_RODATA also apply
here -- the proposed name is fine.

> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 06fed56..2fe0e98 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -12,6 +12,7 @@ config ARM64
>  	select ARCH_HAS_GCOV_PROFILE_ALL
>  	select ARCH_HAS_GIGANTIC_PAGE
>  	select ARCH_HAS_HARDENED_MAPPINGS
> +	select ARCH_HAS_HARDENED_MODULE_MAPPINGS
>  	select ARCH_HAS_KCOV
>  	select ARCH_HAS_SG_CHAIN
>  	select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
> diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug
> index a26d27f..1eebe1f 100644
> --- a/arch/arm64/Kconfig.debug
> +++ b/arch/arm64/Kconfig.debug
> @@ -71,17 +71,6 @@ config DEBUG_WX
>  
>  	  If in doubt, say "Y".
>  
> -config DEBUG_SET_MODULE_RONX
> -	bool "Set loadable kernel module data as NX and text as RO"
> -	depends on MODULES
> -	default y
> -	help
> -	  Is this is set, kernel module text and rodata will be made read-only.
> -	  This is to help catch accidental or malicious attempts to change the
> -	  kernel's executable code.
> -
> -	  If in doubt, say Y.
> -

> +config ARCH_HAS_HARDENED_MODULE_MAPPINGS
> +	def_bool n
> +
> +config HARDENED_MODULE_MAPPINGS
> +	bool "Mark module mappings with stricter permissions (RO/W^X)"
> +	default y
> +	depends on ARCH_HAS_HARDENED_MODULE_MAPPINGS
> +	help
> +	  If this is set, module text and rodata memory will be made read-only,
> +	  and non-text memory will be made non-executable. This provides
> +	  protection against certain security vulnerabilities (e.g. modifying
> +	  code)
> +
> +	  Unless your system has known restrictions or performance issues, it
> +	  is recommended to say Y here.
> +

I was hoping that we'd make this mandatory, as we'd already done for
DEBUG_RODATA.

Takahiro-san did a bit of work towards that in commit 39290b389ea2654f
("module: extend 'rodata=off' boot cmdline parameter to module
mappings").

It would be good to know if there's any reason we can't do that.

Otherwise, this looks fine.

Thanks,
Mark.