[ARM] 3813/1: prevent >= 4G /dev/mem mmap()

Prevent userland from mapping in physical address regions >= 4G by
checking for that in valid_mmap_phys_addr_range().

Unfortunately, we cannot override valid_mmap_phys_addr_range() without
also overriding valid_phys_addr_range(), so copy drivers/char/mem.c's
version of valid_phys_addr_range() over to arch/arm/mm/mmap.c as well.
Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mm/mmap.c

@@ -114,3 +114,25 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
 	}
 }
 
+
+/*
+ * You really shouldn't be using read() or write() on /dev/mem.  This
+ * might go away in the future.
+ */
+int valid_phys_addr_range(unsigned long addr, size_t size)
+{
+	if (addr + size > __pa(high_memory))
+		return 0;
+
+	return 1;
+}
+
+/*
+ * We don't use supersection mappings for mmap() on /dev/mem, which
+ * means that we can't map the memory area above the 4G barrier into
+ * userspace.
+ */
+int valid_mmap_phys_addr_range(unsigned long pfn, size_t size)
+{
+	return !(pfn + (size >> PAGE_SHIFT) > 0x00100000);
+}

include/asm-arm/io.h

@@ -280,6 +280,10 @@ extern void pci_iounmap(struct pci_dev *dev, void __iomem *addr);
 #define BIOVEC_MERGEABLE(vec1, vec2)	\
 	((bvec_to_phys((vec1)) + (vec1)->bv_len) == bvec_to_phys((vec2)))
 
+#define ARCH_HAS_VALID_PHYS_ADDR_RANGE
+extern int valid_phys_addr_range(unsigned long addr, size_t size);
+extern int valid_mmap_phys_addr_range(unsigned long pfn, size_t size);
+
 /*
  * Convert a physical pointer to a virtual kernel pointer for /dev/mem
  * access