/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 <jwer...@chromium.org>
---
drivers/char/mem.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 7e4a9d1296bb..6e0cbe092220 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -340,6 +340,11 @@ static const struct vm_operations_struct mmap_mem_ops = {
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;
--
2.12.2
