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 static struct page **vdso_pages;
  25 static unsigned vdso_size;
  26
  27 static inline void *var_ref(void *p, char *name)
  28 {
  29         if (*(void **)p != (void *)VMAGIC) {
  30                 printk("VDSO: variable %s broken\n", name);
  31                 vdso_enabled = 0;
  32         }
  33         return p;
  34 }
  35
  36 static int __init init_vdso_vars(void)
  37 {
  38         int npages = (vdso_end - vdso_start + PAGE_SIZE - 1) / PAGE_SIZE;
  39         int i;
  40         char *vbase;
  41
  42         vdso_size = npages << PAGE_SHIFT;
  43         vdso_pages = kmalloc(sizeof(struct page *) * npages, GFP_KERNEL);
  44         if (!vdso_pages)
  45                 goto oom;
  46         for (i = 0; i < npages; i++) {
  47                 struct page *p;
  48                 p = alloc_page(GFP_KERNEL);
  49                 if (!p)
  50                         goto oom;
  51                 vdso_pages[i] = p;
  52                 copy_page(page_address(p), vdso_start + i*PAGE_SIZE);
  53         }
  54
  55         vbase = vmap(vdso_pages, npages, 0, PAGE_KERNEL);
  56         if (!vbase)
  57                 goto oom;
  58
  59         if (memcmp(vbase, "\177ELF", 4)) {
  60                 printk("VDSO: I'm broken; not ELF\n");
  61                 vdso_enabled = 0;
  62         }
  63
  64 #define VEXTERN(x) \
  65         *(typeof(__ ## x) **) var_ref(VDSO64_SYMBOL(vbase, x), #x) = &__ ## x;
  66 #include "vextern.h"
  67 #undef VEXTERN
  68         return 0;
  69
  70  oom:
  71         printk("Cannot allocate vdso\n");
  72         vdso_enabled = 0;
  73         return -ENOMEM;
  74 }
  75 __initcall(init_vdso_vars);
  76
  77 struct linux_binprm;
  78
  79 /* Put the vdso above the (randomized) stack with another randomized offset.
  80    This way there is no hole in the middle of address space.
  81    To save memory make sure it is still in the same PTE as the stack top.
  82    This doesn't give that many random bits */
  83 static unsigned long vdso_addr(unsigned long start, unsigned len)
  84 {
  85         unsigned long addr, end;
  86         unsigned offset;
  87         end = (start + PMD_SIZE - 1) & PMD_MASK;
  88         if (end >= TASK_SIZE_MAX)
  89                 end = TASK_SIZE_MAX;
  90         end -= len;
  91         /* This loses some more bits than a modulo, but is cheaper */
  92         offset = get_random_int() & (PTRS_PER_PTE - 1);
  93         addr = start + (offset << PAGE_SHIFT);
  94         if (addr >= end)
  95                 addr = end;
  96         return addr;
  97 }
  98
  99 /* Setup a VMA at program startup for the vsyscall page.
 100    Not called for compat tasks */
 101 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 102 {
 103         struct mm_struct *mm = current->mm;
 104         unsigned long addr;
 105         int ret;
 106
 107         if (!vdso_enabled)
 108                 return 0;
 109
 110         down_write(&mm->mmap_sem);
 111         addr = vdso_addr(mm->start_stack, vdso_size);
 112         addr = get_unmapped_area(NULL, addr, vdso_size, 0, 0);
 113         if (IS_ERR_VALUE(addr)) {
 114                 ret = addr;
 115                 goto up_fail;
 116         }
 117
 118         ret = install_special_mapping(mm, addr, vdso_size,
 119                                       VM_READ|VM_EXEC|
 120                                       VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
 121                                       VM_ALWAYSDUMP,
 122                                       vdso_pages);
 123         if (ret)
 124                 goto up_fail;
 125
 126         current->mm->context.vdso = (void *)addr;
 127 up_fail:
 128         up_write(&mm->mmap_sem);
 129         return ret;
 130 }
 131
 132 static __init int vdso_setup(char *s)
 133 {
 134         vdso_enabled = simple_strtoul(s, NULL, 0);
 135         return 0;
 136 }
 137 __setup("vdso=", vdso_setup);