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
7 #include <linux/sched.h>
8 #include <linux/init.h>
9 #include <linux/random.h>
10 #include <asm/vsyscall.h>
11 #include <asm/vgtod.h>
12 #include <asm/proto.h>
17 #define VEXTERN(x) extern typeof(__ ## x) *vdso_ ## x;
21 extern char vdso_kernel_start[], vdso_start[], vdso_end[];
22 extern unsigned short vdso_sync_cpuid;
24 struct page **vdso_pages;
26 static inline void *var_ref(void *vbase, char *var, char *name)
28 unsigned offset = var - &vdso_kernel_start[0] + VDSO_TEXT_OFFSET;
29 void *p = vbase + offset;
30 if (*(void **)p != (void *)VMAGIC) {
31 printk("VDSO: variable %s broken\n", name);
37 static int __init init_vdso_vars(void)
39 int npages = (vdso_end - vdso_start + PAGE_SIZE - 1) / PAGE_SIZE;
43 vdso_pages = kmalloc(sizeof(struct page *) * npages, GFP_KERNEL);
46 for (i = 0; i < npages; i++) {
48 p = alloc_page(GFP_KERNEL);
52 copy_page(page_address(p), vdso_start + i*PAGE_SIZE);
55 vbase = vmap(vdso_pages, npages, 0, PAGE_KERNEL);
59 if (memcmp(vbase, "\177ELF", 4)) {
60 printk("VDSO: I'm broken; not ELF\n");
64 #define V(x) *(typeof(x) *) var_ref(vbase, (char *)RELOC_HIDE(&x, 0), #x)
66 V(vdso_ ## x) = &__ ## x;
72 printk("Cannot allocate vdso\n");
76 __initcall(init_vdso_vars);
80 /* Put the vdso above the (randomized) stack with another randomized offset.
81 This way there is no hole in the middle of address space.
82 To save memory make sure it is still in the same PTE as the stack top.
83 This doesn't give that many random bits */
84 static unsigned long vdso_addr(unsigned long start, unsigned len)
86 unsigned long addr, end;
88 end = (start + PMD_SIZE - 1) & PMD_MASK;
89 if (end >= TASK_SIZE64)
92 /* This loses some more bits than a modulo, but is cheaper */
93 offset = get_random_int() & (PTRS_PER_PTE - 1);
94 addr = start + (offset << PAGE_SHIFT);
100 /* Setup a VMA at program startup for the vsyscall page.
101 Not called for compat tasks */
102 int arch_setup_additional_pages(struct linux_binprm *bprm, int exstack)
104 struct mm_struct *mm = current->mm;
107 unsigned len = round_up(vdso_end - vdso_start, PAGE_SIZE);
112 down_write(&mm->mmap_sem);
113 addr = vdso_addr(mm->start_stack, len);
114 addr = get_unmapped_area(NULL, addr, len, 0, 0);
115 if (IS_ERR_VALUE(addr)) {
120 ret = install_special_mapping(mm, addr, len,
122 VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
128 current->mm->context.vdso = (void *)addr;
130 up_write(&mm->mmap_sem);
134 static __init int vdso_setup(char *s)
136 vdso_enabled = simple_strtoul(s, NULL, 0);
139 __setup("vdso=", vdso_setup);