[PATCH] powerpc/mm: add devmem_is_allowed() for STRICT_DEVMEM checking

[Josh Boyer]

On Mon, Jan 31, 2011 at 2:16 PM, Steve Best <sfbest at us.ibm.com> wrote:
>    Provide devmem_is_allowed() routine to restrict access to kernel
>    memory from userspace.
>    Set CONFIG_STRICT_DEVMEM config option to switch on checking.
>
> Signed-off-by: Steve Best <sfbest at us.ibm.com>
>
> diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
> index 2d38a50..6805d5d 100644
> --- a/arch/powerpc/Kconfig.debug
> +++ b/arch/powerpc/Kconfig.debug
> @@ -299,4 +299,16 @@ config PPC_EARLY_DEBUG_CPM_ADDR
>          platform probing is done, all platforms selected must
>          share the same address.
>
> +config STRICT_DEVMEM
> +        def_bool y
> +        prompt "Filter access to /dev/mem"
> +        ---help---
> +          This option restricts access to /dev/mem.  If this option is
> +          disabled, you allow userspace access to all memory, including
> +          kernel and userspace memory. Accidental memory access is likely
> +          to be disastrous.
> +          Memory access is required for experts who want to debug the kernel.
> +
> +          If you are unsure, say Y.
> +
>  endmenu
> diff --git a/arch/powerpc/include/asm/page.h b/arch/powerpc/include/asm/page.h
> index 53b64be..f225032 100644
> --- a/arch/powerpc/include/asm/page.h
> +++ b/arch/powerpc/include/asm/page.h
> @@ -262,6 +262,11 @@ extern void copy_user_page(void *to, void *from, unsigned long vaddr,
>                struct page *p);
>  extern int page_is_ram(unsigned long pfn);
>
> +static inline int devmem_is_allowed(unsigned long pfn)
> +{
> +        return 0;
> +}
> +

Er, should this be toggled via CONFIG_STRICT_DEVMEM somehow?  Or I
guess I'm missing why the config option had to be added if not.

josh