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  */
devmem_is_allowed(unsigned long pfn)20 int devmem_is_allowed(unsigned long pfn)
21 {
22 	if (iomem_is_exclusive(PFN_PHYS(pfn)))
23 		return 0;
24 	if (!page_is_ram(pfn))
25 		return 1;
26 	return 0;
27 }
28