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
  14 /*
  15  * devmem_is_allowed() checks to see if /dev/mem access to a certain address
  16  * is valid. The argument is a physical page number.  We mimic x86 here by
  17  * disallowing access to system RAM as well as device-exclusive MMIO regions.
  18  * This effectively disable read()/write() on /dev/mem.
  19  */
  20 int devmem_is_allowed(unsigned long pfn)
  21 {
  22         if (iomem_is_exclusive(pfn << PAGE_SHIFT))
  23                 return 0;
  24         if (!page_is_ram(pfn))
  25                 return 1;
  26         return 0;
  27 }