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
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>
18 #include "vextern.h" /* Just for VMAGIC. */
21 unsigned int __read_mostly vdso_enabled = 1;
23 extern char vdso_start[], vdso_end[];
24 extern unsigned short vdso_sync_cpuid;
26 static struct page **vdso_pages;
27 static unsigned vdso_size;
29 static inline void *var_ref(void *p, char *name)
31 if (*(void **)p != (void *)VMAGIC) {
32 printk("VDSO: variable %s broken\n", name);
38 static int __init init_vdso_vars(void)
40 int npages = (vdso_end - vdso_start + PAGE_SIZE - 1) / PAGE_SIZE;
44 vdso_size = npages << PAGE_SHIFT;
45 vdso_pages = kmalloc(sizeof(struct page *) * npages, GFP_KERNEL);
48 for (i = 0; i < npages; i++) {
50 p = alloc_page(GFP_KERNEL);
54 copy_page(page_address(p), vdso_start + i*PAGE_SIZE);
57 vbase = vmap(vdso_pages, npages, 0, PAGE_KERNEL);
61 if (memcmp(vbase, "\177ELF", 4)) {
62 printk("VDSO: I'm broken; not ELF\n");
67 *(typeof(__ ## x) **) var_ref(VDSO64_SYMBOL(vbase, x), #x) = &__ ## x;
73 printk("Cannot allocate vdso\n");
77 __initcall(init_vdso_vars);
81 /* Put the vdso above the (randomized) stack with another randomized offset.
82 This way there is no hole in the middle of address space.
83 To save memory make sure it is still in the same PTE as the stack top.
84 This doesn't give that many random bits */
85 static unsigned long vdso_addr(unsigned long start, unsigned len)
87 unsigned long addr, end;
89 end = (start + PMD_SIZE - 1) & PMD_MASK;
90 if (end >= TASK_SIZE_MAX)
93 /* This loses some more bits than a modulo, but is cheaper */
94 offset = get_random_int() & (PTRS_PER_PTE - 1);
95 addr = start + (offset << PAGE_SHIFT);
101 /* Setup a VMA at program startup for the vsyscall page.
102 Not called for compat tasks */
103 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
105 struct mm_struct *mm = current->mm;
112 down_write(&mm->mmap_sem);
113 addr = vdso_addr(mm->start_stack, vdso_size);
114 addr = get_unmapped_area(NULL, addr, vdso_size, 0, 0);
115 if (IS_ERR_VALUE(addr)) {
120 current->mm->context.vdso = (void *)addr;
122 ret = install_special_mapping(mm, addr, vdso_size,
124 VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
128 current->mm->context.vdso = NULL;
133 up_write(&mm->mmap_sem);
137 static __init int vdso_setup(char *s)
139 vdso_enabled = simple_strtoul(s, NULL, 0);
142 __setup("vdso=", vdso_setup);