1 /* 2 * Based on arch/arm/mm/mmap.c 3 * 4 * Copyright (C) 2012 ARM Ltd. 5 * 6 * This program is free software; you can redistribute it and/or modify 7 * it under the terms of the GNU General Public License version 2 as 8 * published by the Free Software Foundation. 9 * 10 * This program is distributed in the hope that it will be useful, 11 * but WITHOUT ANY WARRANTY; without even the implied warranty of 12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 13 * GNU General Public License for more details. 14 * 15 * You should have received a copy of the GNU General Public License 16 * along with this program. If not, see <http://www.gnu.org/licenses/>. 17 */ 18 19 #include <linux/elf.h> 20 #include <linux/fs.h> 21 #include <linux/mm.h> 22 #include <linux/mman.h> 23 #include <linux/export.h> 24 #include <linux/shm.h> 25 #include <linux/sched.h> 26 #include <linux/io.h> 27 #include <linux/personality.h> 28 #include <linux/random.h> 29 30 #include <asm/cputype.h> 31 32 /* 33 * Leave enough space between the mmap area and the stack to honour ulimit in 34 * the face of randomisation. 35 */ 36 #define MIN_GAP (SZ_128M + ((STACK_RND_MASK << PAGE_SHIFT) + 1)) 37 #define MAX_GAP (STACK_TOP/6*5) 38 39 static int mmap_is_legacy(void) 40 { 41 if (current->personality & ADDR_COMPAT_LAYOUT) 42 return 1; 43 44 if (rlimit(RLIMIT_STACK) == RLIM_INFINITY) 45 return 1; 46 47 return sysctl_legacy_va_layout; 48 } 49 50 static unsigned long mmap_rnd(void) 51 { 52 unsigned long rnd = 0; 53 54 if (current->flags & PF_RANDOMIZE) 55 rnd = (long)get_random_int() & STACK_RND_MASK; 56 57 return rnd << PAGE_SHIFT; 58 } 59 60 static unsigned long mmap_base(void) 61 { 62 unsigned long gap = rlimit(RLIMIT_STACK); 63 64 if (gap < MIN_GAP) 65 gap = MIN_GAP; 66 else if (gap > MAX_GAP) 67 gap = MAX_GAP; 68 69 return PAGE_ALIGN(STACK_TOP - gap - mmap_rnd()); 70 } 71 72 /* 73 * This function, called very early during the creation of a new process VM 74 * image, sets up which VM layout function to use: 75 */ 76 void arch_pick_mmap_layout(struct mm_struct *mm) 77 { 78 /* 79 * Fall back to the standard layout if the personality bit is set, or 80 * if the expected stack growth is unlimited: 81 */ 82 if (mmap_is_legacy()) { 83 mm->mmap_base = TASK_UNMAPPED_BASE; 84 mm->get_unmapped_area = arch_get_unmapped_area; 85 } else { 86 mm->mmap_base = mmap_base(); 87 mm->get_unmapped_area = arch_get_unmapped_area_topdown; 88 } 89 } 90 EXPORT_SYMBOL_GPL(arch_pick_mmap_layout); 91 92 93 /* 94 * You really shouldn't be using read() or write() on /dev/mem. This might go 95 * away in the future. 96 */ 97 int valid_phys_addr_range(phys_addr_t addr, size_t size) 98 { 99 if (addr < PHYS_OFFSET) 100 return 0; 101 if (addr + size > __pa(high_memory - 1) + 1) 102 return 0; 103 104 return 1; 105 } 106 107 /* 108 * Do not allow /dev/mem mappings beyond the supported physical range. 109 */ 110 int valid_mmap_phys_addr_range(unsigned long pfn, size_t size) 111 { 112 return !(((pfn << PAGE_SHIFT) + size) & ~PHYS_MASK); 113 } 114 115 #ifdef CONFIG_STRICT_DEVMEM 116 117 #include <linux/ioport.h> 118 119 /* 120 * devmem_is_allowed() checks to see if /dev/mem access to a certain address 121 * is valid. The argument is a physical page number. We mimic x86 here by 122 * disallowing access to system RAM as well as device-exclusive MMIO regions. 123 * This effectively disable read()/write() on /dev/mem. 124 */ 125 int devmem_is_allowed(unsigned long pfn) 126 { 127 if (iomem_is_exclusive(pfn << PAGE_SHIFT)) 128 return 0; 129 if (!page_is_ram(pfn)) 130 return 1; 131 return 0; 132 } 133 134 #endif 135