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/slab.h>
  10 #include <linux/init.h>
  11 #include <linux/random.h>
  12 #include <linux/elf.h>
  13 #include <asm/vsyscall.h>
  14 #include <asm/vgtod.h>
  15 #include <asm/proto.h>
  16 #include <asm/vdso.h>
  17
  18 #include "vextern.h"            /* Just for VMAGIC.  */
  19 #undef VEXTERN
  20
  21 unsigned int __read_mostly vdso_enabled = 1;
  22
  23 extern char vdso_start[], vdso_end[];
  24 extern unsigned short vdso_sync_cpuid;
  25
  26 static struct page **vdso_pages;
  27 static unsigned vdso_size;
  28
  29 static inline void *var_ref(void *p, char *name)
  30 {
  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_size = npages << PAGE_SHIFT;
  45         vdso_pages = kmalloc(sizeof(struct page *) * npages, GFP_KERNEL);
  46         if (!vdso_pages)
  47                 goto oom;
  48         for (i = 0; i < npages; i++) {
  49                 struct page *p;
  50                 p = alloc_page(GFP_KERNEL);
  51                 if (!p)
  52                         goto oom;
  53                 vdso_pages[i] = p;
  54                 copy_page(page_address(p), vdso_start + i*PAGE_SIZE);
  55         }
  56
  57         vbase = vmap(vdso_pages, npages, 0, PAGE_KERNEL);
  58         if (!vbase)
  59                 goto oom;
  60
  61         if (memcmp(vbase, "\177ELF", 4)) {
  62                 printk("VDSO: I'm broken; not ELF\n");
  63                 vdso_enabled = 0;
  64         }
  65
  66 #define VEXTERN(x) \
  67         *(typeof(__ ## x) **) var_ref(VDSO64_SYMBOL(vbase, x), #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_SIZE_MAX)
  91                 end = TASK_SIZE_MAX;
  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 uses_interp)
 104 {
 105         struct mm_struct *mm = current->mm;
 106         unsigned long addr;
 107         int ret;
 108
 109         if (!vdso_enabled)
 110                 return 0;
 111
 112         down_write(&mm->mmap_sem);
 113         addr = vdso_addr(mm->start_stack, vdso_size);
 114         addr = get_unmapped_area(NULL, addr, vdso_size, 0, 0);
 115         if (IS_ERR_VALUE(addr)) {
 116                 ret = addr;
 117                 goto up_fail;
 118         }
 119
 120         current->mm->context.vdso = (void *)addr;
 121
 122         ret = install_special_mapping(mm, addr, vdso_size,
 123                                       VM_READ|VM_EXEC|
 124                                       VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
 125                                       VM_ALWAYSDUMP,
 126                                       vdso_pages);
 127         if (ret) {
 128                 current->mm->context.vdso = NULL;
 129                 goto up_fail;
 130         }
 131
 132 up_fail:
 133         up_write(&mm->mmap_sem);
 134         return ret;
 135 }
 136
 137 static __init int vdso_setup(char *s)
 138 {
 139         vdso_enabled = simple_strtoul(s, NULL, 0);
 140         return 0;
 141 }
 142 __setup("vdso=", vdso_setup);