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 <linux/elf.h>
  12 #include <asm/vsyscall.h>
  13 #include <asm/vgtod.h>
  14 #include <asm/proto.h>
  15 #include <asm/vdso.h>
  16
  17 #include "vextern.h"            /* Just for VMAGIC.  */
  18 #undef VEXTERN
  19
  20 unsigned int __read_mostly vdso_enabled = 1;
  21
  22 extern char vdso_start[], vdso_end[];
  23 extern unsigned short vdso_sync_cpuid;
  24
  25 static struct page **vdso_pages;
  26 static unsigned vdso_size;
  27
  28 static inline void *var_ref(void *p, char *name)
  29 {
  30         if (*(void **)p != (void *)VMAGIC) {
  31                 printk("VDSO: variable %s broken\n", name);
  32                 vdso_enabled = 0;
  33         }
  34         return p;
  35 }
  36
  37 static int __init init_vdso_vars(void)
  38 {
  39         int npages = (vdso_end - vdso_start + PAGE_SIZE - 1) / PAGE_SIZE;
  40         int i;
  41         char *vbase;
  42
  43         vdso_size = npages << PAGE_SHIFT;
  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 VEXTERN(x) \
  66         *(typeof(__ ## x) **) var_ref(VDSO64_SYMBOL(vbase, x), #x) = &__ ## x;
  67 #include "vextern.h"
  68 #undef VEXTERN
  69         return 0;
  70
  71  oom:
  72         printk("Cannot allocate vdso\n");
  73         vdso_enabled = 0;
  74         return -ENOMEM;
  75 }
  76 __initcall(init_vdso_vars);
  77
  78 struct linux_binprm;
  79
  80 /* Put the vdso above the (randomized) stack with another randomized offset.
  81    This way there is no hole in the middle of address space.
  82    To save memory make sure it is still in the same PTE as the stack top.
  83    This doesn't give that many random bits */
  84 static unsigned long vdso_addr(unsigned long start, unsigned len)
  85 {
  86         unsigned long addr, end;
  87         unsigned offset;
  88         end = (start + PMD_SIZE - 1) & PMD_MASK;
  89         if (end >= TASK_SIZE_MAX)
  90                 end = TASK_SIZE_MAX;
  91         end -= len;
  92         /* This loses some more bits than a modulo, but is cheaper */
  93         offset = get_random_int() & (PTRS_PER_PTE - 1);
  94         addr = start + (offset << PAGE_SHIFT);
  95         if (addr >= end)
  96                 addr = end;
  97         return addr;
  98 }
  99
 100 /* Setup a VMA at program startup for the vsyscall page.
 101    Not called for compat tasks */
 102 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 103 {
 104         struct mm_struct *mm = current->mm;
 105         unsigned long addr;
 106         int ret;
 107
 108         if (!vdso_enabled)
 109                 return 0;
 110
 111         down_write(&mm->mmap_sem);
 112         addr = vdso_addr(mm->start_stack, vdso_size);
 113         addr = get_unmapped_area(NULL, addr, vdso_size, 0, 0);
 114         if (IS_ERR_VALUE(addr)) {
 115                 ret = addr;
 116                 goto up_fail;
 117         }
 118
 119         current->mm->context.vdso = (void *)addr;
 120
 121         ret = install_special_mapping(mm, addr, vdso_size,
 122                                       VM_READ|VM_EXEC|
 123                                       VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
 124                                       VM_ALWAYSDUMP,
 125                                       vdso_pages);
 126         if (ret) {
 127                 current->mm->context.vdso = NULL;
 128                 goto up_fail;
 129         }
 130
 131 up_fail:
 132         up_write(&mm->mmap_sem);
 133         return ret;
 134 }
 135
 136 static __init int vdso_setup(char *s)
 137 {
 138         vdso_enabled = simple_strtoul(s, NULL, 0);
 139         return 0;
 140 }
 141 __setup("vdso=", vdso_setup);