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

[Josh Boyer]

On Mon, Jan 31, 2011 at 2:25 PM, Josh Boyer <jwboyer at gmail.com> wrote:
> 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.

Nevermind.  I see that it's done in the drivers/char/mem.c file.
Should have looked more first.

josh