1 /*
2 * Set up the VMAs to tell the VM about the vDSO.
3 * Copyright 2007 Andi Kleen, SUSE Labs.
4 * Subject to the GPL, v.2
5 */
6 #include <linux/mm.h>
7 #include <linux/err.h>
8 #include <linux/sched.h>
9 #include <linux/slab.h>
10 #include <linux/init.h>
11 #include <linux/random.h>
12 #include <linux/elf.h>
13 #include <asm/vsyscall.h>
14 #include <asm/vgtod.h>
15 #include <asm/proto.h>
16 #include <asm/vdso.h>
17 #include <asm/page.h>
18
19 unsigned int __read_mostly vdso_enabled = 1;
20
21 extern char vdso_start[], vdso_end[];
22 extern unsigned short vdso_sync_cpuid;
23
24 extern struct page *vdso_pages[];
25 static unsigned vdso_size;
26
patch_vdso(void * vdso,size_t len)27 static void __init patch_vdso(void *vdso, size_t len)
28 {
29 Elf64_Ehdr *hdr = vdso;
30 Elf64_Shdr *sechdrs, *alt_sec = 0;
31 char *secstrings;
32 void *alt_data;
33 int i;
34
35 BUG_ON(len < sizeof(Elf64_Ehdr));
36 BUG_ON(memcmp(hdr->e_ident, ELFMAG, SELFMAG) != 0);
37
38 sechdrs = (void *)hdr + hdr->e_shoff;
39 secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
40
41 for (i = 1; i < hdr->e_shnum; i++) {
42 Elf64_Shdr *shdr = &sechdrs[i];
43 if (!strcmp(secstrings + shdr->sh_name, ".altinstructions")) {
44 alt_sec = shdr;
45 goto found;
46 }
47 }
48
49 /* If we get here, it's probably a bug. */
50 pr_warning("patch_vdso: .altinstructions not found\n");
51 return; /* nothing to patch */
52
53 found:
54 alt_data = (void *)hdr + alt_sec->sh_offset;
55 apply_alternatives(alt_data, alt_data + alt_sec->sh_size);
56 }
57
init_vdso(void)58 static int __init init_vdso(void)
59 {
60 int npages = (vdso_end - vdso_start + PAGE_SIZE - 1) / PAGE_SIZE;
61 int i;
62
63 patch_vdso(vdso_start, vdso_end - vdso_start);
64
65 vdso_size = npages << PAGE_SHIFT;
66 for (i = 0; i < npages; i++)
67 vdso_pages[i] = virt_to_page(vdso_start + i*PAGE_SIZE);
68
69 return 0;
70 }
71 subsys_initcall(init_vdso);
72
73 struct linux_binprm;
74
75 /* Put the vdso above the (randomized) stack with another randomized offset.
76 This way there is no hole in the middle of address space.
77 To save memory make sure it is still in the same PTE as the stack top.
78 This doesn't give that many random bits */
vdso_addr(unsigned long start,unsigned len)79 static unsigned long vdso_addr(unsigned long start, unsigned len)
80 {
81 unsigned long addr, end;
82 unsigned offset;
83 end = (start + PMD_SIZE - 1) & PMD_MASK;
84 if (end >= TASK_SIZE_MAX)
85 end = TASK_SIZE_MAX;
86 end -= len;
87 /* This loses some more bits than a modulo, but is cheaper */
88 offset = get_random_int() & (PTRS_PER_PTE - 1);
89 addr = start + (offset << PAGE_SHIFT);
90 if (addr >= end)
91 addr = end;
92
93 /*
94 * page-align it here so that get_unmapped_area doesn't
95 * align it wrongfully again to the next page. addr can come in 4K
96 * unaligned here as a result of stack start randomization.
97 */
98 addr = PAGE_ALIGN(addr);
99 addr = align_addr(addr, NULL, ALIGN_VDSO);
100
101 return addr;
102 }
103
104 /* Setup a VMA at program startup for the vsyscall page.
105 Not called for compat tasks */
arch_setup_additional_pages(struct linux_binprm * bprm,int uses_interp)106 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
107 {
108 struct mm_struct *mm = current->mm;
109 unsigned long addr;
110 int ret;
111
112 if (!vdso_enabled)
113 return 0;
114
115 down_write(&mm->mmap_sem);
116 addr = vdso_addr(mm->start_stack, vdso_size);
117 addr = get_unmapped_area(NULL, addr, vdso_size, 0, 0);
118 if (IS_ERR_VALUE(addr)) {
119 ret = addr;
120 goto up_fail;
121 }
122
123 current->mm->context.vdso = (void *)addr;
124
125 ret = install_special_mapping(mm, addr, vdso_size,
126 VM_READ|VM_EXEC|
127 VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
128 VM_ALWAYSDUMP,
129 vdso_pages);
130 if (ret) {
131 current->mm->context.vdso = NULL;
132 goto up_fail;
133 }
134
135 up_fail:
136 up_write(&mm->mmap_sem);
137 return ret;
138 }
139
vdso_setup(char * s)140 static __init int vdso_setup(char *s)
141 {
142 vdso_enabled = simple_strtoul(s, NULL, 0);
143 return 0;
144 }
145 __setup("vdso=", vdso_setup);
146