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/init.h>
10 #include <linux/random.h>
11 #include <asm/vsyscall.h>
12 #include <asm/vgtod.h>
13 #include <asm/proto.h>
14 #include <asm/vdso.h>
15
16 #include "vextern.h" /* Just for VMAGIC. */
17 #undef VEXTERN
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 static struct page **vdso_pages;
25 static unsigned vdso_size;
26
var_ref(void * p,char * name)27 static inline void *var_ref(void *p, char *name)
28 {
29 if (*(void **)p != (void *)VMAGIC) {
30 printk("VDSO: variable %s broken\n", name);
31 vdso_enabled = 0;
32 }
33 return p;
34 }
35
init_vdso_vars(void)36 static int __init init_vdso_vars(void)
37 {
38 int npages = (vdso_end - vdso_start + PAGE_SIZE - 1) / PAGE_SIZE;
39 int i;
40 char *vbase;
41
42 vdso_size = npages << PAGE_SHIFT;
43 vdso_pages = kmalloc(sizeof(struct page *) * npages, GFP_KERNEL);
44 if (!vdso_pages)
45 goto oom;
46 for (i = 0; i < npages; i++) {
47 struct page *p;
48 p = alloc_page(GFP_KERNEL);
49 if (!p)
50 goto oom;
51 vdso_pages[i] = p;
52 copy_page(page_address(p), vdso_start + i*PAGE_SIZE);
53 }
54
55 vbase = vmap(vdso_pages, npages, 0, PAGE_KERNEL);
56 if (!vbase)
57 goto oom;
58
59 if (memcmp(vbase, "\177ELF", 4)) {
60 printk("VDSO: I'm broken; not ELF\n");
61 vdso_enabled = 0;
62 }
63
64 #define VEXTERN(x) \
65 *(typeof(__ ## x) **) var_ref(VDSO64_SYMBOL(vbase, x), #x) = &__ ## x;
66 #include "vextern.h"
67 #undef VEXTERN
68 return 0;
69
70 oom:
71 printk("Cannot allocate vdso\n");
72 vdso_enabled = 0;
73 return -ENOMEM;
74 }
75 __initcall(init_vdso_vars);
76
77 struct linux_binprm;
78
79 /* Put the vdso above the (randomized) stack with another randomized offset.
80 This way there is no hole in the middle of address space.
81 To save memory make sure it is still in the same PTE as the stack top.
82 This doesn't give that many random bits */
vdso_addr(unsigned long start,unsigned len)83 static unsigned long vdso_addr(unsigned long start, unsigned len)
84 {
85 unsigned long addr, end;
86 unsigned offset;
87 end = (start + PMD_SIZE - 1) & PMD_MASK;
88 if (end >= TASK_SIZE64)
89 end = TASK_SIZE64;
90 end -= len;
91 /* This loses some more bits than a modulo, but is cheaper */
92 offset = get_random_int() & (PTRS_PER_PTE - 1);
93 addr = start + (offset << PAGE_SHIFT);
94 if (addr >= end)
95 addr = end;
96 return addr;
97 }
98
99 /* Setup a VMA at program startup for the vsyscall page.
100 Not called for compat tasks */
arch_setup_additional_pages(struct linux_binprm * bprm,int uses_interp)101 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
102 {
103 struct mm_struct *mm = current->mm;
104 unsigned long addr;
105 int ret;
106
107 if (!vdso_enabled)
108 return 0;
109
110 down_write(&mm->mmap_sem);
111 addr = vdso_addr(mm->start_stack, vdso_size);
112 addr = get_unmapped_area(NULL, addr, vdso_size, 0, 0);
113 if (IS_ERR_VALUE(addr)) {
114 ret = addr;
115 goto up_fail;
116 }
117
118 ret = install_special_mapping(mm, addr, vdso_size,
119 VM_READ|VM_EXEC|
120 VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
121 VM_ALWAYSDUMP,
122 vdso_pages);
123 if (ret)
124 goto up_fail;
125
126 current->mm->context.vdso = (void *)addr;
127 up_fail:
128 up_write(&mm->mmap_sem);
129 return ret;
130 }
131
vdso_setup(char * s)132 static __init int vdso_setup(char *s)
133 {
134 vdso_enabled = simple_strtoul(s, NULL, 0);
135 return 0;
136 }
137 __setup("vdso=", vdso_setup);
138