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         vunmap(vbase);
  71         return 0;
  72
  73  oom:
  74         printk("Cannot allocate vdso\n");
  75         vdso_enabled = 0;
  76         return -ENOMEM;
  77 }
  78 subsys_initcall(init_vdso_vars);
  79
  80 struct linux_binprm;
  81
  82 /* Put the vdso above the (randomized) stack with another randomized offset.
  83    This way there is no hole in the middle of address space.
  84    To save memory make sure it is still in the same PTE as the stack top.
  85    This doesn't give that many random bits */
  86 static unsigned long vdso_addr(unsigned long start, unsigned len)
  87 {
  88         unsigned long addr, end;
  89         unsigned offset;
  90         end = (start + PMD_SIZE - 1) & PMD_MASK;
  91         if (end >= TASK_SIZE_MAX)
  92                 end = TASK_SIZE_MAX;
  93         end -= len;
  94         /* This loses some more bits than a modulo, but is cheaper */
  95         offset = get_random_int() & (PTRS_PER_PTE - 1);
  96         addr = start + (offset << PAGE_SHIFT);
  97         if (addr >= end)
  98                 addr = end;
  99         return addr;
 100 }
 101
 102 /* Setup a VMA at program startup for the vsyscall page.
 103    Not called for compat tasks */
 104 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 105 {
 106         struct mm_struct *mm = current->mm;
 107         unsigned long addr;
 108         int ret;
 109
 110         if (!vdso_enabled)
 111                 return 0;
 112
 113         down_write(&mm->mmap_sem);
 114         addr = vdso_addr(mm->start_stack, vdso_size);
 115         addr = get_unmapped_area(NULL, addr, vdso_size, 0, 0);
 116         if (IS_ERR_VALUE(addr)) {
 117                 ret = addr;
 118                 goto up_fail;
 119         }
 120
 121         current->mm->context.vdso = (void *)addr;
 122
 123         ret = install_special_mapping(mm, addr, vdso_size,
 124                                       VM_READ|VM_EXEC|
 125                                       VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
 126                                       VM_ALWAYSDUMP,
 127                                       vdso_pages);
 128         if (ret) {
 129                 current->mm->context.vdso = NULL;
 130                 goto up_fail;
 131         }
 132
 133 up_fail:
 134         up_write(&mm->mmap_sem);
 135         return ret;
 136 }
 137
 138 static __init int vdso_setup(char *s)
 139 {
 140         vdso_enabled = simple_strtoul(s, NULL, 0);
 141         return 0;
 142 }
 143 __setup("vdso=", vdso_setup);