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/init.h>
  10 #include <linux/random.h>
  11 #include <asm/vsyscall.h>
  12 #include <asm/vgtod.h>
  13 #include <asm/proto.h>
  14 #include <asm/vdso.h>
  15
  16 #include "vextern.h"            /* Just for VMAGIC.  */
  17 #undef VEXTERN
  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 struct page **vdso_pages;
  25
  26 static inline void *var_ref(void *p, char *name)
  27 {
  28         if (*(void **)p != (void *)VMAGIC) {
  29                 printk("VDSO: variable %s broken\n", name);
  30                 vdso_enabled = 0;
  31         }
  32         return p;
  33 }
  34
  35 static int __init init_vdso_vars(void)
  36 {
  37         int npages = (vdso_end - vdso_start + PAGE_SIZE - 1) / PAGE_SIZE;
  38         int i;
  39         char *vbase;
  40
  41         vdso_pages = kmalloc(sizeof(struct page *) * npages, GFP_KERNEL);
  42         if (!vdso_pages)
  43                 goto oom;
  44         for (i = 0; i < npages; i++) {
  45                 struct page *p;
  46                 p = alloc_page(GFP_KERNEL);
  47                 if (!p)
  48                         goto oom;
  49                 vdso_pages[i] = p;
  50                 copy_page(page_address(p), vdso_start + i*PAGE_SIZE);
  51         }
  52
  53         vbase = vmap(vdso_pages, npages, 0, PAGE_KERNEL);
  54         if (!vbase)
  55                 goto oom;
  56
  57         if (memcmp(vbase, "\177ELF", 4)) {
  58                 printk("VDSO: I'm broken; not ELF\n");
  59                 vdso_enabled = 0;
  60         }
  61
  62 #define VEXTERN(x) \
  63         *(typeof(__ ## x) **) var_ref(VDSO64_SYMBOL(vbase, x), #x) = &__ ## x;
  64 #include "vextern.h"
  65 #undef VEXTERN
  66         return 0;
  67
  68  oom:
  69         printk("Cannot allocate vdso\n");
  70         vdso_enabled = 0;
  71         return -ENOMEM;
  72 }
  73 __initcall(init_vdso_vars);
  74
  75 struct linux_binprm;
  76
  77 /* Put the vdso above the (randomized) stack with another randomized offset.
  78    This way there is no hole in the middle of address space.
  79    To save memory make sure it is still in the same PTE as the stack top.
  80    This doesn't give that many random bits */
  81 static unsigned long vdso_addr(unsigned long start, unsigned len)
  82 {
  83         unsigned long addr, end;
  84         unsigned offset;
  85         end = (start + PMD_SIZE - 1) & PMD_MASK;
  86         if (end >= TASK_SIZE64)
  87                 end = TASK_SIZE64;
  88         end -= len;
  89         /* This loses some more bits than a modulo, but is cheaper */
  90         offset = get_random_int() & (PTRS_PER_PTE - 1);
  91         addr = start + (offset << PAGE_SHIFT);
  92         if (addr >= end)
  93                 addr = end;
  94         return addr;
  95 }
  96
  97 /* Setup a VMA at program startup for the vsyscall page.
  98    Not called for compat tasks */
  99 int arch_setup_additional_pages(struct linux_binprm *bprm, int exstack)
 100 {
 101         struct mm_struct *mm = current->mm;
 102         unsigned long addr;
 103         int ret;
 104         unsigned len = round_up(vdso_end - vdso_start, PAGE_SIZE);
 105
 106         if (!vdso_enabled)
 107                 return 0;
 108
 109         down_write(&mm->mmap_sem);
 110         addr = vdso_addr(mm->start_stack, len);
 111         addr = get_unmapped_area(NULL, addr, len, 0, 0);
 112         if (IS_ERR_VALUE(addr)) {
 113                 ret = addr;
 114                 goto up_fail;
 115         }
 116
 117         ret = install_special_mapping(mm, addr, len,
 118                                       VM_READ|VM_EXEC|
 119                                       VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
 120                                       VM_ALWAYSDUMP,
 121                                       vdso_pages);
 122         if (ret)
 123                 goto up_fail;
 124
 125         current->mm->context.vdso = (void *)addr;
 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);