arch/x86/vdso/vma.c

   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
  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 extern struct page *vdso_pages[];
  25 static unsigned vdso_size;
  26
  27 static 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
  53 found:
  54         alt_data = (void *)hdr + alt_sec->sh_offset;
  55         apply_alternatives(alt_data, alt_data + alt_sec->sh_size);
  56 }
  57
  58 static 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 }
  71 subsys_initcall(init_vdso);
  72
  73 struct 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 */
  79 static 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 */
  97 int 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
 126 up_fail:
 127         up_write(&mm->mmap_sem);
 128         return ret;
 129 }
 130
 131 static __init int vdso_setup(char *s)
 132 {
 133         vdso_enabled = simple_strtoul(s, NULL, 0);
 134         return 0;
 135 }
 136 __setup("vdso=", vdso_setup);