[PATCH] arm64: always enable DEBUG_RODATA and remove the Kconfig option

[Ard Biesheuvel]

On 25 August 2016 at 18:23, Mark Rutland <mark.rutland at arm.com> wrote:
> Follow the example set by x86 in commit 9ccaf77cf05915f5 ("x86/mm:
> Always enable CONFIG_DEBUG_RODATA and remove the Kconfig option"), and
> make these protections a fundamental security feature rather than an
> opt-in. This also results in a minor code simplification.
>
> For those rare cases when users wish to disable this protection (e.g.
> for debugging), this can be done by passing 'rodata=off' on the command
> line.
>
> As DEBUG_RODATA_ALIGN is only intended to address a performance/memory
> tradeoff, and does not affect correctness, this is left user-selectable.
> DEBUG_MODULE_RONX is also left user-selectable until the core code
> provides a boot-time option to disable the protection for debugging
> use-cases.
>
> Signed-off-by: Mark Rutland <mark.rutland at arm.com>

Acked-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>

About time!


> Cc: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Kees Cook <keescook at chromium.org>
> Cc: Laura Abbott <labbott at redhat.com>
> Cc: Will Deacon <will.deacon at arm.com>
> ---
>  arch/arm64/Kconfig       |  3 +++
>  arch/arm64/Kconfig.debug | 10 ----------
>  arch/arm64/kernel/insn.c |  2 +-
>  3 files changed, 4 insertions(+), 11 deletions(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index bc3f00f..43d6134 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -122,6 +122,9 @@ config ARCH_PHYS_ADDR_T_64BIT
>  config MMU
>         def_bool y
>
> +config DEBUG_RODATA
> +       def_bool y
> +
>  config ARM64_PAGE_SHIFT
>         int
>         default 16 if ARM64_64K_PAGES
> diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug
> index 0cc758c..b661fe7 100644
> --- a/arch/arm64/Kconfig.debug
> +++ b/arch/arm64/Kconfig.debug
> @@ -49,16 +49,6 @@ config DEBUG_SET_MODULE_RONX
>
>           If in doubt, say Y.
>
> -config DEBUG_RODATA
> -       bool "Make kernel text and rodata read-only"
> -       default y
> -       help
> -         If this is set, kernel 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 DEBUG_RODATA
>         bool "Align linker sections up to SECTION_SIZE"
> diff --git a/arch/arm64/kernel/insn.c b/arch/arm64/kernel/insn.c
> index 63f9432..178488f 100644
> --- a/arch/arm64/kernel/insn.c
> +++ b/arch/arm64/kernel/insn.c
> @@ -96,7 +96,7 @@ static void __kprobes *patch_map(void *addr, int fixmap)
>
>         if (module && IS_ENABLED(CONFIG_DEBUG_SET_MODULE_RONX))
>                 page = vmalloc_to_page(addr);
> -       else if (!module && IS_ENABLED(CONFIG_DEBUG_RODATA))
> +       else if (!module)
>                 page = pfn_to_page(PHYS_PFN(__pa(addr)));
>         else
>                 return addr;
> --
> 2.7.4
>