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Subject[PATCH 3.16 063/233] drivers: char: mem: Check for address space wraparound with mmap()
3.16.48-rc1 review patch.  If anyone has any objections, please let me know.


From: Julius Werner <>

commit b299cde245b0b76c977f4291162cf668e087b408 upstream.

/dev/mem currently allows mmap() mappings that wrap around the end of
the physical address space, which should probably be illegal. It
circumvents the existing STRICT_DEVMEM permission check because the loop
immediately terminates (as the start address is already higher than the
end address). On the x86_64 architecture it will then cause a panic
(from the BUG(start >= end) in arch/x86/mm/pat.c:reserve_memtype()).

This patch adds an explicit check to make sure offset + size will not
wrap around in the physical address type.

Signed-off-by: Julius Werner <>
Signed-off-by: Greg Kroah-Hartman <>
Signed-off-by: Ben Hutchings <>
drivers/char/mem.c | 5 +++++
1 file changed, 5 insertions(+)

--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -329,6 +329,11 @@ static const struct vm_operations_struct
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;
+ /* It's illegal to wrap around the end of the physical address space. */
+ if (offset + (phys_addr_t)size < offset)
+ return -EINVAL;

if (!valid_mmap_phys_addr_range(vma->vm_pgoff, size))
return -EINVAL;
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