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 unsigned long arch_mmap_rnd(void) 51 { 52 unsigned long rnd; 53 54 rnd = (unsigned long)get_random_int() & STACK_RND_MASK; 55 56 return rnd << PAGE_SHIFT; 57 } 58 59 static unsigned long mmap_base(unsigned long rnd) 60 { 61 unsigned long gap = rlimit(RLIMIT_STACK); 62 63 if (gap < MIN_GAP) 64 gap = MIN_GAP; 65 else if (gap > MAX_GAP) 66 gap = MAX_GAP; 67 68 return PAGE_ALIGN(STACK_TOP - gap - rnd); 69 } 70 71 /* 72 * This function, called very early during the creation of a new process VM 73 * image, sets up which VM layout function to use: 74 */ 75 void arch_pick_mmap_layout(struct mm_struct *mm) 76 { 77 unsigned long random_factor = 0UL; 78 79 if (current->flags & PF_RANDOMIZE) 80 random_factor = arch_mmap_rnd(); 81 82 /* 83 * Fall back to the standard layout if the personality bit is set, or 84 * if the expected stack growth is unlimited: 85 */ 86 if (mmap_is_legacy()) { 87 mm->mmap_base = TASK_UNMAPPED_BASE + random_factor; 88 mm->get_unmapped_area = arch_get_unmapped_area; 89 } else { 90 mm->mmap_base = mmap_base(random_factor); 91 mm->get_unmapped_area = arch_get_unmapped_area_topdown; 92 } 93 } 94 EXPORT_SYMBOL_GPL(arch_pick_mmap_layout); 95 96 97 /* 98 * You really shouldn't be using read() or write() on /dev/mem. This might go 99 * away in the future. 100 */ 101 int valid_phys_addr_range(phys_addr_t addr, size_t size) 102 { 103 if (addr < PHYS_OFFSET) 104 return 0; 105 if (addr + size > __pa(high_memory - 1) + 1) 106 return 0; 107 108 return 1; 109 } 110 111 /* 112 * Do not allow /dev/mem mappings beyond the supported physical range. 113 */ 114 int valid_mmap_phys_addr_range(unsigned long pfn, size_t size) 115 { 116 return !(((pfn << PAGE_SHIFT) + size) & ~PHYS_MASK); 117 } 118 119 #ifdef CONFIG_STRICT_DEVMEM 120 121 #include <linux/ioport.h> 122 123 /* 124 * devmem_is_allowed() checks to see if /dev/mem access to a certain address 125 * is valid. The argument is a physical page number. We mimic x86 here by 126 * disallowing access to system RAM as well as device-exclusive MMIO regions. 127 * This effectively disable read()/write() on /dev/mem. 128 */ 129 int devmem_is_allowed(unsigned long pfn) 130 { 131 if (iomem_is_exclusive(pfn << PAGE_SHIFT)) 132 return 0; 133 if (!page_is_ram(pfn)) 134 return 1; 135 return 0; 136 } 137 138 #endif 139