diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index 93ae8aee1780..95e948627fd0 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -111,6 +111,10 @@ build_mmio_write(__writeq, "q", unsigned long, "r", )
 
 #endif
 
+#define ARCH_HAS_VALID_PHYS_ADDR_RANGE
+extern int valid_phys_addr_range(phys_addr_t addr, size_t size);
+extern int valid_mmap_phys_addr_range(unsigned long pfn, size_t size);
+
 /**
  *	virt_to_phys	-	map virtual addresses to physical
  *	@address: address to remap
diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index 62285fe77b0f..155ecbac9e28 100644
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -33,6 +33,8 @@
 #include <linux/compat.h>
 #include <asm/elf.h>
 
+#include "physaddr.h"
+
 struct va_alignment __read_mostly va_align = {
 	.flags = -1,
 };
@@ -220,3 +222,17 @@ bool mmap_address_hint_valid(unsigned long addr, unsigned long len)
 
 	return (addr > DEFAULT_MAP_WINDOW) == (addr + len > DEFAULT_MAP_WINDOW);
 }
+
+/* Can we access it for direct reading/writing? Must be RAM: */
+int valid_phys_addr_range(phys_addr_t addr, size_t count)
+{
+	return addr + count <= __pa(high_memory);
+}
+
+/* Can we access it through mmap? Must be a valid physical address: */
+int valid_mmap_phys_addr_range(unsigned long pfn, size_t count)
+{
+	phys_addr_t addr = (phys_addr_t)pfn << PAGE_SHIFT;
+
+	return phys_addr_valid(addr + count - 1);
+}
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 970e1242a282..6aefe5370e5b 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -343,6 +343,10 @@ static int mmap_mem(struct file *file, struct vm_area_struct *vma)
 	size_t size = vma->vm_end - vma->vm_start;
 	phys_addr_t offset = (phys_addr_t)vma->vm_pgoff << PAGE_SHIFT;
 
+	/* Does it even fit in phys_addr_t? */
+	if (offset >> PAGE_SHIFT != vma->vm_pgoff)
+		return -EINVAL;
+
 	/* It's illegal to wrap around the end of the physical address space. */
 	if (offset + (phys_addr_t)size - 1 < offset)
 		return -EINVAL;