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 #include <asm/page.h>
  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 extern struct page *vdso_pages[];
  25 static unsigned vdso_size;
  26
  27 #ifdef CONFIG_X86_X32_ABI
  28 extern char vdsox32_start[], vdsox32_end[];
  29 extern struct page *vdsox32_pages[];
  30 static unsigned vdsox32_size;
  31
  32 static void __init patch_vdsox32(void *vdso, size_t len)
  33 {
  34         Elf32_Ehdr *hdr = vdso;
  35         Elf32_Shdr *sechdrs, *alt_sec = 0;
  36         char *secstrings;
  37         void *alt_data;
  38         int i;
  39
  40         BUG_ON(len < sizeof(Elf32_Ehdr));
  41         BUG_ON(memcmp(hdr->e_ident, ELFMAG, SELFMAG) != 0);
  42
  43         sechdrs = (void *)hdr + hdr->e_shoff;
  44         secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
  45
  46         for (i = 1; i < hdr->e_shnum; i++) {
  47                 Elf32_Shdr *shdr = &sechdrs[i];
  48                 if (!strcmp(secstrings + shdr->sh_name, ".altinstructions")) {
  49                         alt_sec = shdr;
  50                         goto found;
  51                 }
  52         }
  53
  54         /* If we get here, it's probably a bug. */
  55         pr_warning("patch_vdsox32: .altinstructions not found\n");
  56         return;  /* nothing to patch */
  57
  58 found:
  59         alt_data = (void *)hdr + alt_sec->sh_offset;
  60         apply_alternatives(alt_data, alt_data + alt_sec->sh_size);
  61 }
  62 #endif
  63
  64 static void __init patch_vdso64(void *vdso, size_t len)
  65 {
  66         Elf64_Ehdr *hdr = vdso;
  67         Elf64_Shdr *sechdrs, *alt_sec = 0;
  68         char *secstrings;
  69         void *alt_data;
  70         int i;
  71
  72         BUG_ON(len < sizeof(Elf64_Ehdr));
  73         BUG_ON(memcmp(hdr->e_ident, ELFMAG, SELFMAG) != 0);
  74
  75         sechdrs = (void *)hdr + hdr->e_shoff;
  76         secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
  77
  78         for (i = 1; i < hdr->e_shnum; i++) {
  79                 Elf64_Shdr *shdr = &sechdrs[i];
  80                 if (!strcmp(secstrings + shdr->sh_name, ".altinstructions")) {
  81                         alt_sec = shdr;
  82                         goto found;
  83                 }
  84         }
  85
  86         /* If we get here, it's probably a bug. */
  87         pr_warning("patch_vdso64: .altinstructions not found\n");
  88         return;  /* nothing to patch */
  89
  90 found:
  91         alt_data = (void *)hdr + alt_sec->sh_offset;
  92         apply_alternatives(alt_data, alt_data + alt_sec->sh_size);
  93 }
  94
  95 static int __init init_vdso(void)
  96 {
  97         int npages = (vdso_end - vdso_start + PAGE_SIZE - 1) / PAGE_SIZE;
  98         int i;
  99
 100         patch_vdso64(vdso_start, vdso_end - vdso_start);
 101
 102         vdso_size = npages << PAGE_SHIFT;
 103         for (i = 0; i < npages; i++)
 104                 vdso_pages[i] = virt_to_page(vdso_start + i*PAGE_SIZE);
 105
 106 #ifdef CONFIG_X86_X32_ABI
 107         patch_vdsox32(vdsox32_start, vdsox32_end - vdsox32_start);
 108         npages = (vdsox32_end - vdsox32_start + PAGE_SIZE - 1) / PAGE_SIZE;
 109         vdsox32_size = npages << PAGE_SHIFT;
 110         for (i = 0; i < npages; i++)
 111                 vdsox32_pages[i] = virt_to_page(vdsox32_start + i*PAGE_SIZE);
 112 #endif
 113
 114         return 0;
 115 }
 116 subsys_initcall(init_vdso);
 117
 118 struct linux_binprm;
 119
 120 /* Put the vdso above the (randomized) stack with another randomized offset.
 121    This way there is no hole in the middle of address space.
 122    To save memory make sure it is still in the same PTE as the stack top.
 123    This doesn't give that many random bits */
 124 static unsigned long vdso_addr(unsigned long start, unsigned len)
 125 {
 126         unsigned long addr, end;
 127         unsigned offset;
 128         end = (start + PMD_SIZE - 1) & PMD_MASK;
 129         if (end >= TASK_SIZE_MAX)
 130                 end = TASK_SIZE_MAX;
 131         end -= len;
 132         /* This loses some more bits than a modulo, but is cheaper */
 133         offset = get_random_int() & (PTRS_PER_PTE - 1);
 134         addr = start + (offset << PAGE_SHIFT);
 135         if (addr >= end)
 136                 addr = end;
 137
 138         /*
 139          * page-align it here so that get_unmapped_area doesn't
 140          * align it wrongfully again to the next page. addr can come in 4K
 141          * unaligned here as a result of stack start randomization.
 142          */
 143         addr = PAGE_ALIGN(addr);
 144         addr = align_vdso_addr(addr);
 145
 146         return addr;
 147 }
 148
 149 /* Setup a VMA at program startup for the vsyscall page.
 150    Not called for compat tasks */
 151 static int setup_additional_pages(struct linux_binprm *bprm,
 152                                   int uses_interp,
 153                                   struct page **pages,
 154                                   unsigned size)
 155 {
 156         struct mm_struct *mm = current->mm;
 157         unsigned long addr;
 158         int ret;
 159
 160         if (!vdso_enabled)
 161                 return 0;
 162
 163         down_write(&mm->mmap_sem);
 164         addr = vdso_addr(mm->start_stack, size);
 165         addr = get_unmapped_area(NULL, addr, size, 0, 0);
 166         if (IS_ERR_VALUE(addr)) {
 167                 ret = addr;
 168                 goto up_fail;
 169         }
 170
 171         current->mm->context.vdso = (void *)addr;
 172
 173         ret = install_special_mapping(mm, addr, size,
 174                                       VM_READ|VM_EXEC|
 175                                       VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
 176                                       pages);
 177         if (ret) {
 178                 current->mm->context.vdso = NULL;
 179                 goto up_fail;
 180         }
 181
 182 up_fail:
 183         up_write(&mm->mmap_sem);
 184         return ret;
 185 }
 186
 187 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 188 {
 189         return setup_additional_pages(bprm, uses_interp, vdso_pages,
 190                                       vdso_size);
 191 }
 192
 193 #ifdef CONFIG_X86_X32_ABI
 194 int x32_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 195 {
 196         return setup_additional_pages(bprm, uses_interp, vdsox32_pages,
 197                                       vdsox32_size);
 198 }
 199 #endif
 200
 201 static __init int vdso_setup(char *s)
 202 {
 203         vdso_enabled = simple_strtoul(s, NULL, 0);
 204         return 0;
 205 }
 206 __setup("vdso=", vdso_setup);