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 } 28