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
 19unsigned int __read_mostly vdso_enabled = 1;
 20
 21extern char vdso_start[], vdso_end[];
 22extern unsigned short vdso_sync_cpuid;
 23
 24extern struct page *vdso_pages[];
 25static unsigned vdso_size;
 26
 27static 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
 53found:
 54	alt_data = (void *)hdr + alt_sec->sh_offset;
 55	apply_alternatives(alt_data, alt_data + alt_sec->sh_size);
 56}
 57
 58static 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}
 71subsys_initcall(init_vdso);
 72
 73struct 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 */
 79static 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	return addr;
 93}
 94
 95/* Setup a VMA at program startup for the vsyscall page.
 96   Not called for compat tasks */
 97int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 98{
 99	struct mm_struct *mm = current->mm;
100	unsigned long addr;
101	int ret;
102
103	if (!vdso_enabled)
104		return 0;
105
106	down_write(&mm->mmap_sem);
107	addr = vdso_addr(mm->start_stack, vdso_size);
108	addr = get_unmapped_area(NULL, addr, vdso_size, 0, 0);
109	if (IS_ERR_VALUE(addr)) {
110		ret = addr;
111		goto up_fail;
112	}
113
114	current->mm->context.vdso = (void *)addr;
115
116	ret = install_special_mapping(mm, addr, vdso_size,
117				      VM_READ|VM_EXEC|
118				      VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
119				      VM_ALWAYSDUMP,
120				      vdso_pages);
121	if (ret) {
122		current->mm->context.vdso = NULL;
123		goto up_fail;
124	}
125
126up_fail:
127	up_write(&mm->mmap_sem);
128	return ret;
129}
130
131static __init int vdso_setup(char *s)
132{
133	vdso_enabled = simple_strtoul(s, NULL, 0);
134	return 0;
135}
136__setup("vdso=", vdso_setup);