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 unsigned int __read_mostly vdso_enabled = 1;
20 extern char vdso_start[], vdso_end[];
21 extern unsigned short vdso_sync_cpuid;
23 static struct page **vdso_pages;
24 static unsigned vdso_size;
26 static void __init patch_vdso(void *vdso, size_t len)
28 Elf64_Ehdr *hdr = vdso;
29 Elf64_Shdr *sechdrs, *alt_sec = 0;
34 BUG_ON(len < sizeof(Elf64_Ehdr));
35 BUG_ON(memcmp(hdr->e_ident, ELFMAG, SELFMAG) != 0);
37 sechdrs = (void *)hdr + hdr->e_shoff;
38 secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
40 for (i = 1; i < hdr->e_shnum; i++) {
41 Elf64_Shdr *shdr = &sechdrs[i];
42 if (!strcmp(secstrings + shdr->sh_name, ".altinstructions")) {
48 /* If we get here, it's probably a bug. */
49 pr_warning("patch_vdso: .altinstructions not found\n");
50 return; /* nothing to patch */
53 alt_data = (void *)hdr + alt_sec->sh_offset;
54 apply_alternatives(alt_data, alt_data + alt_sec->sh_size);
57 static int __init init_vdso_vars(void)
59 int npages = (vdso_end - vdso_start + PAGE_SIZE - 1) / PAGE_SIZE;
62 patch_vdso(vdso_start, vdso_end - vdso_start);
64 vdso_size = npages << PAGE_SHIFT;
65 vdso_pages = kmalloc(sizeof(struct page *) * npages, GFP_KERNEL);
68 for (i = 0; i < npages; i++) {
70 p = alloc_page(GFP_KERNEL);
74 copy_page(page_address(p), vdso_start + i*PAGE_SIZE);
80 printk("Cannot allocate vdso\n");
84 subsys_initcall(init_vdso_vars);
88 /* Put the vdso above the (randomized) stack with another randomized offset.
89 This way there is no hole in the middle of address space.
90 To save memory make sure it is still in the same PTE as the stack top.
91 This doesn't give that many random bits */
92 static unsigned long vdso_addr(unsigned long start, unsigned len)
94 unsigned long addr, end;
96 end = (start + PMD_SIZE - 1) & PMD_MASK;
97 if (end >= TASK_SIZE_MAX)
100 /* This loses some more bits than a modulo, but is cheaper */
101 offset = get_random_int() & (PTRS_PER_PTE - 1);
102 addr = start + (offset << PAGE_SHIFT);
108 /* Setup a VMA at program startup for the vsyscall page.
109 Not called for compat tasks */
110 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
112 struct mm_struct *mm = current->mm;
119 down_write(&mm->mmap_sem);
120 addr = vdso_addr(mm->start_stack, vdso_size);
121 addr = get_unmapped_area(NULL, addr, vdso_size, 0, 0);
122 if (IS_ERR_VALUE(addr)) {
127 current->mm->context.vdso = (void *)addr;
129 ret = install_special_mapping(mm, addr, vdso_size,
131 VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
135 current->mm->context.vdso = NULL;
140 up_write(&mm->mmap_sem);
144 static __init int vdso_setup(char *s)
146 vdso_enabled = simple_strtoul(s, NULL, 0);
149 __setup("vdso=", vdso_setup);