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 #ifdef CONFIG_COMPAT 55 if (test_thread_flag(TIF_32BIT)) 56 rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1); 57 else 58 #endif 59 rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1); 60 return rnd << PAGE_SHIFT; 61 } 62 63 static unsigned long mmap_base(unsigned long rnd) 64 { 65 unsigned long gap = rlimit(RLIMIT_STACK); 66 67 if (gap < MIN_GAP) 68 gap = MIN_GAP; 69 else if (gap > MAX_GAP) 70 gap = MAX_GAP; 71 72 return PAGE_ALIGN(STACK_TOP - gap - rnd); 73 } 74 75 /* 76 * This function, called very early during the creation of a new process VM 77 * image, sets up which VM layout function to use: 78 */ 79 void arch_pick_mmap_layout(struct mm_struct *mm) 80 { 81 unsigned long random_factor = 0UL; 82 83 if (current->flags & PF_RANDOMIZE) 84 random_factor = arch_mmap_rnd(); 85 86 /* 87 * Fall back to the standard layout if the personality bit is set, or 88 * if the expected stack growth is unlimited: 89 */ 90 if (mmap_is_legacy()) { 91 mm->mmap_base = TASK_UNMAPPED_BASE + random_factor; 92 mm->get_unmapped_area = arch_get_unmapped_area; 93 } else { 94 mm->mmap_base = mmap_base(random_factor); 95 mm->get_unmapped_area = arch_get_unmapped_area_topdown; 96 } 97 } 98 99 /* 100 * You really shouldn't be using read() or write() on /dev/mem. This might go 101 * away in the future. 102 */ 103 int valid_phys_addr_range(phys_addr_t addr, size_t size) 104 { 105 if (addr < PHYS_OFFSET) 106 return 0; 107 if (addr + size > __pa(high_memory - 1) + 1) 108 return 0; 109 110 return 1; 111 } 112 113 /* 114 * Do not allow /dev/mem mappings beyond the supported physical range. 115 */ 116 int valid_mmap_phys_addr_range(unsigned long pfn, size_t size) 117 { 118 return !(((pfn << PAGE_SHIFT) + size) & ~PHYS_MASK); 119 } 120 121 #ifdef CONFIG_STRICT_DEVMEM 122 123 #include <linux/ioport.h> 124 125 /* 126 * devmem_is_allowed() checks to see if /dev/mem access to a certain address 127 * is valid. The argument is a physical page number. We mimic x86 here by 128 * disallowing access to system RAM as well as device-exclusive MMIO regions. 129 * This effectively disable read()/write() on /dev/mem. 130 */ 131 int devmem_is_allowed(unsigned long pfn) 132 { 133 if (iomem_is_exclusive(pfn << PAGE_SHIFT)) 134 return 0; 135 if (!page_is_ram(pfn)) 136 return 1; 137 return 0; 138 } 139 140 #endif 141