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/memblock.h> 22 #include <linux/mm.h> 23 #include <linux/mman.h> 24 #include <linux/export.h> 25 #include <linux/shm.h> 26 #include <linux/sched/signal.h> 27 #include <linux/sched/mm.h> 28 #include <linux/io.h> 29 #include <linux/personality.h> 30 #include <linux/random.h> 31 32 #include <asm/cputype.h> 33 34 /* 35 * Leave enough space between the mmap area and the stack to honour ulimit in 36 * the face of randomisation. 37 */ 38 #define MIN_GAP (SZ_128M) 39 #define MAX_GAP (STACK_TOP/6*5) 40 41 static int mmap_is_legacy(void) 42 { 43 if (current->personality & ADDR_COMPAT_LAYOUT) 44 return 1; 45 46 if (rlimit(RLIMIT_STACK) == RLIM_INFINITY) 47 return 1; 48 49 return sysctl_legacy_va_layout; 50 } 51 52 unsigned long arch_mmap_rnd(void) 53 { 54 unsigned long rnd; 55 56 #ifdef CONFIG_COMPAT 57 if (test_thread_flag(TIF_32BIT)) 58 rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1); 59 else 60 #endif 61 rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1); 62 return rnd << PAGE_SHIFT; 63 } 64 65 static unsigned long mmap_base(unsigned long rnd) 66 { 67 unsigned long gap = rlimit(RLIMIT_STACK); 68 unsigned long pad = (STACK_RND_MASK << PAGE_SHIFT) + stack_guard_gap; 69 70 /* Values close to RLIM_INFINITY can overflow. */ 71 if (gap + pad > gap) 72 gap += pad; 73 74 if (gap < MIN_GAP) 75 gap = MIN_GAP; 76 else if (gap > MAX_GAP) 77 gap = MAX_GAP; 78 79 return PAGE_ALIGN(STACK_TOP - gap - rnd); 80 } 81 82 /* 83 * This function, called very early during the creation of a new process VM 84 * image, sets up which VM layout function to use: 85 */ 86 void arch_pick_mmap_layout(struct mm_struct *mm) 87 { 88 unsigned long random_factor = 0UL; 89 90 if (current->flags & PF_RANDOMIZE) 91 random_factor = arch_mmap_rnd(); 92 93 /* 94 * Fall back to the standard layout if the personality bit is set, or 95 * if the expected stack growth is unlimited: 96 */ 97 if (mmap_is_legacy()) { 98 mm->mmap_base = TASK_UNMAPPED_BASE + random_factor; 99 mm->get_unmapped_area = arch_get_unmapped_area; 100 } else { 101 mm->mmap_base = mmap_base(random_factor); 102 mm->get_unmapped_area = arch_get_unmapped_area_topdown; 103 } 104 } 105 106 /* 107 * You really shouldn't be using read() or write() on /dev/mem. This might go 108 * away in the future. 109 */ 110 int valid_phys_addr_range(phys_addr_t addr, size_t size) 111 { 112 /* 113 * Check whether addr is covered by a memory region without the 114 * MEMBLOCK_NOMAP attribute, and whether that region covers the 115 * entire range. In theory, this could lead to false negatives 116 * if the range is covered by distinct but adjacent memory regions 117 * that only differ in other attributes. However, few of such 118 * attributes have been defined, and it is debatable whether it 119 * follows that /dev/mem read() calls should be able traverse 120 * such boundaries. 121 */ 122 return memblock_is_region_memory(addr, size) && 123 memblock_is_map_memory(addr); 124 } 125 126 /* 127 * Do not allow /dev/mem mappings beyond the supported physical range. 128 */ 129 int valid_mmap_phys_addr_range(unsigned long pfn, size_t size) 130 { 131 return !(((pfn << PAGE_SHIFT) + size) & ~PHYS_MASK); 132 } 133 134 #ifdef CONFIG_STRICT_DEVMEM 135 136 #include <linux/ioport.h> 137 138 /* 139 * devmem_is_allowed() checks to see if /dev/mem access to a certain address 140 * is valid. The argument is a physical page number. We mimic x86 here by 141 * disallowing access to system RAM as well as device-exclusive MMIO regions. 142 * This effectively disable read()/write() on /dev/mem. 143 */ 144 int devmem_is_allowed(unsigned long pfn) 145 { 146 if (iomem_is_exclusive(pfn << PAGE_SHIFT)) 147 return 0; 148 if (!page_is_ram(pfn)) 149 return 1; 150 return 0; 151 } 152 153 #endif 154