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

[Steve Best]

    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;
+}
+
 #ifdef CONFIG_PPC_SMLPAR
 void arch_free_page(struct page *page, int order);
 #define HAVE_ARCH_FREE_PAGE