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

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Message-ID: <5005f110-2279-9ac7-c9c5-1894b8f6387d@arm.com>
Date:   Thu, 19 Jan 2017 11:43:25 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Laura Abbott <labbott@...hat.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Mark Rutland <mark.rutland@....com>, linux-doc@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        "James E.J. Bottomley" <jejb@...isc-linux.org>,
        Pavel Machek <pavel@....cz>, "H. Peter Anvin" <hpa@...or.com>,
        kernel-hardening@...ts.openwall.com, Rob Herring <robh@...nel.org>,
        Jessica Yu <jeyu@...hat.com>, Jonathan Corbet <corbet@....net>,
        Helge Deller <deller@....de>, x86@...nel.org,
        Russell King <linux@...linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        Len Brown <len.brown@...el.com>, linux-s390@...r.kernel.org,
        Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org, linux-parisc@...r.kernel.org,
        linux-pm@...r.kernel.org, "Rafael J. Wysocki" <rjw@...ysocki.net>,
        linux-kernel@...r.kernel.org,
        Jason Wessel <jason.wessel@...driver.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH 2/2] security: Change name of CONFIG_DEBUG_SET_MODULE_RONX

Hi Laura,

On 19/01/17 01:29, 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.
> 
> Signed-off-by: Laura Abbott <labbott@...hat.com>
> ---

[...]

> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 09aff28..ef852e4 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -8,6 +8,7 @@ config ARM
>  	select ARCH_HAVE_CUSTOM_GPIO_H
>  	select ARCH_HAS_GCOV_PROFILE_ALL
>  	select ARCH_HAS_HARDENED_MAPPINGS if MMU && !XIP_KERNEL
> +	select ARCH_HAS_HARDENED_MODULE_MAPPINGS if MMU
>  	select ARCH_MIGHT_HAVE_PC_PARPORT
>  	select ARCH_SUPPORTS_ATOMIC_RMW
>  	select ARCH_USE_BUILTIN_BSWAP
> diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
> index d83f7c3..426d271 100644
> --- a/arch/arm/Kconfig.debug
> +++ b/arch/arm/Kconfig.debug
> @@ -1738,17 +1738,6 @@ config PID_IN_CONTEXTIDR
>  	  additional instructions during context switch. Say Y here only if you
>  	  are planning to use hardware trace tools with this kernel.
>  
> -config DEBUG_SET_MODULE_RONX
> -	bool "Set loadable kernel module data as NX and text as RO"
> -	depends on MODULES && MMU
> -	---help---
> -	  This option helps catch unintended modifications to loadable
> -	  kernel module's text and read-only data. It also prevents execution
> -	  of module data. Such protection may interfere with run-time code
> -	  patching and dynamic kernel tracing - and they might also protect
> -	  against certain classes of kernel exploits.
> -	  If in doubt, say "N".
> -
>  source "drivers/hwtracing/coresight/Kconfig"
>  
>  endmenu

[...]

> --- 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 DEBUG_ALIGN_RODATA
>  	depends on ARCH_HAS_HARDENED_MAPPINGS
>  	bool "Align linker sections up to SECTION_SIZE"

[...]

> --- a/arch/s390/Kconfig
> +++ b/arch/s390/Kconfig
> @@ -69,6 +69,7 @@ config S390
>  	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_UBSAN_SANITIZE_ALL
> diff --git a/arch/s390/Kconfig.debug b/arch/s390/Kconfig.debug
> index 26c5d5be..57f8ea9 100644
> --- a/arch/s390/Kconfig.debug
> +++ b/arch/s390/Kconfig.debug
> @@ -17,7 +17,4 @@ config S390_PTDUMP
>  	  kernel.
>  	  If in doubt, say "N"
>  
> -config DEBUG_SET_MODULE_RONX
> -	def_bool y
> -	depends on MODULES
>  endmenu
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 9d80cd8..38ce850 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -51,6 +51,7 @@ config X86
>  	select ARCH_HAS_FAST_MULTIPLIER
>  	select ARCH_HAS_GCOV_PROFILE_ALL
>  	select ARCH_HAS_HARDENED_MAPPINGS
> +	select ARCH_HAS_HARDENED_MODULE_MAPPINGS
>  	select ARCH_HAS_KCOV			if X86_64
>  	select ARCH_HAS_MMIO_FLUSH
>  	select ARCH_HAS_PMEM_API		if X86_64
> diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
> index 67eec55..69cdd0b 100644
> --- a/arch/x86/Kconfig.debug
> +++ b/arch/x86/Kconfig.debug
> @@ -109,17 +109,6 @@ 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
> -	---help---
> -	  This option helps catch unintended modifications to loadable
> -	  kernel module's text and read-only data. It also prevents execution
> -	  of module data. Such protection may interfere with run-time code
> -	  patching and dynamic kernel tracing - and they might also protect
> -	  against certain classes of kernel exploits.
> -	  If in doubt, say "N".
> -
>  config DEBUG_NX_TEST
>  	tristate "Testcase for the NX non-executable stack feature"
>  	depends on DEBUG_KERNEL && m

[...]

> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -174,6 +174,22 @@ config HARDENED_PAGE_MAPPINGS
>  	  Unless your system has known restrictions or performance issues, it
>  	  is recommended to say Y here.
>  
> +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

It would seem that this ends up losing the previous dependency on
MODULES - is that intentional?

Robin.

> +	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.
> +
>  source security/selinux/Kconfig
>  source security/smack/Kconfig
>  source security/tomoyo/Kconfig
>