lib/devmem_is_allowed.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * A generic version of devmem_is_allowed.
   4  *
   5  * Based on arch/arm64/mm/mmap.c
   6  *
   7  * Copyright (C) 2020 Google, Inc.
   8  * Copyright (C) 2012 ARM Ltd.
   9  */
  10
  11 #include <linux/mm.h>
  12 #include <linux/ioport.h>
  13 #include <linux/io.h>
  14
  15 /*
  16  * devmem_is_allowed() checks to see if /dev/mem access to a certain address
  17  * is valid. The argument is a physical page number.  We mimic x86 here by
  18  * disallowing access to system RAM as well as device-exclusive MMIO regions.
  19  * This effectively disable read()/write() on /dev/mem.
  20  */
  21 int devmem_is_allowed(unsigned long pfn)
  22 {
  23         if (iomem_is_exclusive(PFN_PHYS(pfn)))
  24                 return 0;
  25         if (!page_is_ram(pfn))
  26                 return 1;
  27         return 0;
  28 }