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         ret = install_special_mapping(mm, addr, vdso_size,
 120                                       VM_READ|VM_EXEC|
 121                                       VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
 122                                       VM_ALWAYSDUMP,
 123                                       vdso_pages);
 124         if (ret)
 125                 goto up_fail;
 126
 127         current->mm->context.vdso = (void *)addr;
 128 up_fail:
 129         up_write(&mm->mmap_sem);
 130         return ret;
 131 }
 132
 133 static __init int vdso_setup(char *s)
 134 {
 135         vdso_enabled = simple_strtoul(s, NULL, 0);
 136         return 0;
 137 }
 138 __setup("vdso=", vdso_setup);