powerpc: Implement CONFIG_STRICT_DEVMEM

As described in the help text in the patch, this token restricts general
access to /dev/mem as a way of increasing the security. Specifically, access
to exclusive IOMEM and kernel RAM is denied unless CONFIG_STRICT_DEVMEM is
set to 'n'.

Implement the 'devmem_is_allowed()' interface for Powerpc. It will be
called from range_is_allowed() when userpsace attempts to access /dev/mem.

This patch is based on an earlier patch from Steve Best and with input from
Paul Mackerras and Scott Wood.

[BenH] Fixed a typo or two and removed the generic change which should
       be submitted as a separate patch

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/arch/powerpc/include/asm/page.h b/arch/powerpc/include/asm/page.h
index dd9c4fd038e..9d7485c7e6f 100644
--- a/arch/powerpc/include/asm/page.h
+++ b/arch/powerpc/include/asm/page.h
@@ -290,6 +290,7 @@ extern void clear_user_page(void *page, unsigned long vaddr, struct page *pg);
 extern void copy_user_page(void *to, void *from, unsigned long vaddr,
 		struct page *p);
 extern int page_is_ram(unsigned long pfn);
+extern int devmem_is_allowed(unsigned long pfn);
 
 #ifdef CONFIG_PPC_SMLPAR
 void arch_free_page(struct page *page, int order);