1 // SPDX-License-Identifier: GPL-2.0-only
3 * Based on arch/arm/mm/mmap.c
5 * Copyright (C) 2012 ARM Ltd.
10 #include <linux/memblock.h>
12 #include <linux/mman.h>
13 #include <linux/export.h>
14 #include <linux/shm.h>
15 #include <linux/sched/signal.h>
16 #include <linux/sched/mm.h>
18 #include <linux/personality.h>
19 #include <linux/random.h>
21 #include <asm/cputype.h>
24 * Leave enough space between the mmap area and the stack to honour ulimit in
25 * the face of randomisation.
27 #define MIN_GAP (SZ_128M)
28 #define MAX_GAP (STACK_TOP/6*5)
30 static int mmap_is_legacy(struct rlimit *rlim_stack)
32 if (current->personality & ADDR_COMPAT_LAYOUT)
35 if (rlim_stack->rlim_cur == RLIM_INFINITY)
38 return sysctl_legacy_va_layout;
41 unsigned long arch_mmap_rnd(void)
46 if (test_thread_flag(TIF_32BIT))
47 rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1);
50 rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
51 return rnd << PAGE_SHIFT;
54 static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
56 unsigned long gap = rlim_stack->rlim_cur;
57 unsigned long pad = (STACK_RND_MASK << PAGE_SHIFT) + stack_guard_gap;
59 /* Values close to RLIM_INFINITY can overflow. */
65 else if (gap > MAX_GAP)
68 return PAGE_ALIGN(STACK_TOP - gap - rnd);
72 * This function, called very early during the creation of a new process VM
73 * image, sets up which VM layout function to use:
75 void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
77 unsigned long random_factor = 0UL;
79 if (current->flags & PF_RANDOMIZE)
80 random_factor = arch_mmap_rnd();
83 * Fall back to the standard layout if the personality bit is set, or
84 * if the expected stack growth is unlimited:
86 if (mmap_is_legacy(rlim_stack)) {
87 mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
88 mm->get_unmapped_area = arch_get_unmapped_area;
90 mm->mmap_base = mmap_base(random_factor, rlim_stack);
91 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
96 * You really shouldn't be using read() or write() on /dev/mem. This might go
99 int valid_phys_addr_range(phys_addr_t addr, size_t size)
102 * Check whether addr is covered by a memory region without the
103 * MEMBLOCK_NOMAP attribute, and whether that region covers the
104 * entire range. In theory, this could lead to false negatives
105 * if the range is covered by distinct but adjacent memory regions
106 * that only differ in other attributes. However, few of such
107 * attributes have been defined, and it is debatable whether it
108 * follows that /dev/mem read() calls should be able traverse
111 return memblock_is_region_memory(addr, size) &&
112 memblock_is_map_memory(addr);
116 * Do not allow /dev/mem mappings beyond the supported physical range.
118 int valid_mmap_phys_addr_range(unsigned long pfn, size_t size)
120 return !(((pfn << PAGE_SHIFT) + size) & ~PHYS_MASK);
123 #ifdef CONFIG_STRICT_DEVMEM
125 #include <linux/ioport.h>
128 * devmem_is_allowed() checks to see if /dev/mem access to a certain address
129 * is valid. The argument is a physical page number. We mimic x86 here by
130 * disallowing access to system RAM as well as device-exclusive MMIO regions.
131 * This effectively disable read()/write() on /dev/mem.
133 int devmem_is_allowed(unsigned long pfn)
135 if (iomem_is_exclusive(pfn << PAGE_SHIFT))
137 if (!page_is_ram(pfn))