On Wed, Jan 18, 2017 at 5:29 PM, Laura Abbott <labbott@xxxxxxxxxx> wrote: > > Despite the word 'debug' in CONFIG_DEBUG_RODATA, this kernel option > provides key security features that are to be expected on a modern > system. Change the name to CONFIG_HARDENED_PAGE_MAPPINGS which more > accurately describes what this option is intended to do. Oh thank you. Yes, this is badly needed. I might prefer to see this as two patches, though: Move DEBUG_RODATA to top-level arch/Kconfig, (and add ARCH_HAS_[bikeshed]). Rename DEBUG_RODATA to [bikeshed] (We should do a similar renaming for DEBUG_SET_MODULE_RONX too.) Another thing that might be even cleaner would be to entirely invert the logic. Something like CONFIG_ARCH_MISSING_[bikeshed]? > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig > index 186c4c2..09aff28 100644 > --- a/arch/arm/Kconfig > +++ b/arch/arm/Kconfig > @@ -7,6 +7,7 @@ config ARM > select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST > select ARCH_HAVE_CUSTOM_GPIO_H > select ARCH_HAS_GCOV_PROFILE_ALL > + select ARCH_HAS_HARDENED_MAPPINGS if MMU && !XIP_KERNEL > select ARCH_MIGHT_HAVE_PC_PARPORT > select ARCH_SUPPORTS_ATOMIC_RMW > select ARCH_USE_BUILTIN_BSWAP > diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig > index f68e8ec..e770dc9 100644 > --- a/arch/arm/mm/Kconfig > +++ b/arch/arm/mm/Kconfig > @@ -1051,21 +1051,9 @@ config ARCH_SUPPORTS_BIG_ENDIAN > This option specifies the architecture can support big endian > operation. > > -config DEBUG_RODATA > - bool "Make kernel text and rodata read-only" > - depends on MMU && !XIP_KERNEL > - default y if CPU_V7 These changes aren't correctly representing the ARM state. I think the ARCH_HAS is correct, but I'm not sure the best way to include the "default y if CPU_V7". > --- a/security/Kconfig > +++ b/security/Kconfig > @@ -158,6 +158,22 @@ config HARDENED_USERCOPY_PAGESPAN > been removed. This config is intended to be used only while > trying to find such users. > > +config ARCH_HAS_HARDENED_MAPPINGS > + def_bool n > + > +config HARDENED_PAGE_MAPPINGS > + bool "Mark kernel mappings with stricter permissions (RO/W^X)" > + default y > + depends on ARCH_HAS_HARDENED_MAPPINGS > + help > + If this is set, kernel text and rodata memory will be made read-only, > + and non-text memory will be made non-executable. This provides > + protection against certain security attacks (e.g. executing the heap > + or modifying text). > + > + 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 Should this go in arch/Kconfig or security/Kconfig? I'm starting to think we need a top-level kernel security Kconfig (the gcc plugins are starting to pile up in arch/Kconfig, for example). I think since this is arch specific, maybe arch/Kconfig? (Arguably, HARDENED_USERCOPY shouldn't be in security/Kconfig either, since security/Kconfig is mostly LSM or userspace-facing stuff? I dunno.) As for the bikeshed on the naming, I like "KERNEL_RWX", and it likely doesn't need "STRICT", IMO. CONFIG_KERNEL_RWX ? I don't have a strong opinion beyond removing "DEBUG" from the name. :) -Kees -- Kees Cook Nexus Security -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
