arch/x86_64/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/init.h>
  10 #include <linux/random.h>
  11 #include <asm/vsyscall.h>
  12 #include <asm/vgtod.h>
  13 #include <asm/proto.h>
  14 #include "voffset.h"
  15
  16 int vdso_enabled = 1;
  17
  18 #define VEXTERN(x) extern typeof(__ ## x) *vdso_ ## x;
  19 #include "vextern.h"
  20 #undef VEXTERN
  21
  22 extern char vdso_kernel_start[], vdso_start[], vdso_end[];
  23 extern unsigned short vdso_sync_cpuid;
  24
  25 struct page **vdso_pages;
  26
  27 static inline void *var_ref(void *vbase, char *var, char *name)
  28 {
  29         unsigned offset = var - &vdso_kernel_start[0] + VDSO_TEXT_OFFSET;
  30         void *p = vbase + offset;
  31         if (*(void **)p != (void *)VMAGIC) {
  32                 printk("VDSO: variable %s broken\n", name);
  33                 vdso_enabled = 0;
  34         }
  35         return p;
  36 }
  37
  38 static int __init init_vdso_vars(void)
  39 {
  40         int npages = (vdso_end - vdso_start + PAGE_SIZE - 1) / PAGE_SIZE;
  41         int i;
  42         char *vbase;
  43
  44         vdso_pages = kmalloc(sizeof(struct page *) * npages, GFP_KERNEL);
  45         if (!vdso_pages)
  46                 goto oom;
  47         for (i = 0; i < npages; i++) {
  48                 struct page *p;
  49                 p = alloc_page(GFP_KERNEL);
  50                 if (!p)
  51                         goto oom;
  52                 vdso_pages[i] = p;
  53                 copy_page(page_address(p), vdso_start + i*PAGE_SIZE);
  54         }
  55
  56         vbase = vmap(vdso_pages, npages, 0, PAGE_KERNEL);
  57         if (!vbase)
  58                 goto oom;
  59
  60         if (memcmp(vbase, "\177ELF", 4)) {
  61                 printk("VDSO: I'm broken; not ELF\n");
  62                 vdso_enabled = 0;
  63         }
  64
  65 #define V(x) *(typeof(x) *) var_ref(vbase, (char *)RELOC_HIDE(&x, 0), #x)
  66 #define VEXTERN(x) \
  67         V(vdso_ ## x) = &__ ## x;
  68 #include "vextern.h"
  69 #undef VEXTERN
  70         return 0;
  71
  72  oom:
  73         printk("Cannot allocate vdso\n");
  74         vdso_enabled = 0;
  75         return -ENOMEM;
  76 }
  77 __initcall(init_vdso_vars);
  78
  79 struct linux_binprm;
  80
  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)
  86 {
  87         unsigned long addr, end;
  88         unsigned offset;
  89         end = (start + PMD_SIZE - 1) & PMD_MASK;
  90         if (end >= TASK_SIZE64)
  91                 end = TASK_SIZE64;
  92         end -= len;
  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);
  96         if (addr >= end)
  97                 addr = end;
  98         return addr;
  99 }
 100
 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 exstack)
 104 {
 105         struct mm_struct *mm = current->mm;
 106         unsigned long addr;
 107         int ret;
 108         unsigned len = round_up(vdso_end - vdso_start, PAGE_SIZE);
 109
 110         if (!vdso_enabled)
 111                 return 0;
 112
 113         down_write(&mm->mmap_sem);
 114         addr = vdso_addr(mm->start_stack, len);
 115         addr = get_unmapped_area(NULL, addr, len, 0, 0);
 116         if (IS_ERR_VALUE(addr)) {
 117                 ret = addr;
 118                 goto up_fail;
 119         }
 120
 121         ret = install_special_mapping(mm, addr, len,
 122                                       VM_READ|VM_EXEC|
 123                                       VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
 124                                       VM_ALWAYSDUMP,
 125                                       vdso_pages);
 126         if (ret)
 127                 goto up_fail;
 128
 129         current->mm->context.vdso = (void *)addr;
 130 up_fail:
 131         up_write(&mm->mmap_sem);
 132         return ret;
 133 }
 134
 135 static __init int vdso_setup(char *s)
 136 {
 137         vdso_enabled = simple_strtoul(s, NULL, 0);
 138         return 0;
 139 }
 140 __setup("vdso=", vdso_setup);