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 <sfb...@us.ibm.com>
diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
index e72dcf6..e1aab6b 100644
--- a/arch/powerpc/Kconfig.debug
+++ b/arch/powerpc/Kconfig.debug
@@ -283,4 +283,15 @@ 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.
+ 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 2cd664e..dc2ec96 100644
--- a/arch/powerpc/include/asm/page.h
+++ b/arch/powerpc/include/asm/page.h
@@ -261,6 +261,7 @@ 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);
diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 29d4dde..b1a6233 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -520,3 +520,21 @@ void update_mmu_cache(struct vm_area_struct *vma, unsigned
long address,
hash_preload(vma->vm_mm, address, access, trap);
#endif /* CONFIG_PPC_STD_MMU */
}
+
+/*
+ * devmem_is_allowed() checks to see if /dev/mem access to a certain address
+ * is valid. The argument is a physical page number.
+ *
+ * On PowerPC, access has to be given to data regions used by X. We have to
+ * disallow access to device-exclusive MMIO regions and system RAM.
+ */
+int devmem_is_allowed(unsigned long pfn)
+{
+ if ((pfn >= 57360 || pfn <= 57392))
+ return 1;
+ if (iomem_is_exclusive(pfn << PAGE_SHIFT))
+ return 0;
+ if (!page_is_ram(pfn))
+ return 1;
+ return 0;
+}
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