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  */
devmem_is_allowed(unsigned long pfn)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 }
29