arch/x86/entry/vdso/vma.c

   1 /*
   2  * Copyright 2007 Andi Kleen, SUSE Labs.
   3  * Subject to the GPL, v.2
   4  *
   5  * This contains most of the x86 vDSO kernel-side code.
   6  */
   7 #include <linux/mm.h>
   8 #include <linux/err.h>
   9 #include <linux/sched.h>
  10 #include <linux/sched/task_stack.h>
  11 #include <linux/slab.h>
  12 #include <linux/init.h>
  13 #include <linux/random.h>
  14 #include <linux/elf.h>
  15 #include <linux/cpu.h>
  16 #include <linux/ptrace.h>
  17 #include <asm/pvclock.h>
  18 #include <asm/vgtod.h>
  19 #include <asm/proto.h>
  20 #include <asm/vdso.h>
  21 #include <asm/vvar.h>
  22 #include <asm/page.h>
  23 #include <asm/desc.h>
  24 #include <asm/cpufeature.h>
  25
  26 #if defined(CONFIG_X86_64)
  27 unsigned int __read_mostly vdso64_enabled = 1;
  28 #endif
  29
  30 void __init init_vdso_image(const struct vdso_image *image)
  31 {
  32         BUG_ON(image->size % PAGE_SIZE != 0);
  33
  34         apply_alternatives((struct alt_instr *)(image->data + image->alt),
  35                            (struct alt_instr *)(image->data + image->alt +
  36                                                 image->alt_len));
  37 }
  38
  39 struct linux_binprm;
  40
  41 static int vdso_fault(const struct vm_special_mapping *sm,
  42                       struct vm_area_struct *vma, struct vm_fault *vmf)
  43 {
  44         const struct vdso_image *image = vma->vm_mm->context.vdso_image;
  45
  46         if (!image || (vmf->pgoff << PAGE_SHIFT) >= image->size)
  47                 return VM_FAULT_SIGBUS;
  48
  49         vmf->page = virt_to_page(image->data + (vmf->pgoff << PAGE_SHIFT));
  50         get_page(vmf->page);
  51         return 0;
  52 }
  53
  54 static void vdso_fix_landing(const struct vdso_image *image,
  55                 struct vm_area_struct *new_vma)
  56 {
  57 #if defined CONFIG_X86_32 || defined CONFIG_IA32_EMULATION
  58         if (in_ia32_syscall() && image == &vdso_image_32) {
  59                 struct pt_regs *regs = current_pt_regs();
  60                 unsigned long vdso_land = image->sym_int80_landing_pad;
  61                 unsigned long old_land_addr = vdso_land +
  62                         (unsigned long)current->mm->context.vdso;
  63
  64                 /* Fixing userspace landing - look at do_fast_syscall_32 */
  65                 if (regs->ip == old_land_addr)
  66                         regs->ip = new_vma->vm_start + vdso_land;
  67         }
  68 #endif
  69 }
  70
  71 static int vdso_mremap(const struct vm_special_mapping *sm,
  72                 struct vm_area_struct *new_vma)
  73 {
  74         unsigned long new_size = new_vma->vm_end - new_vma->vm_start;
  75         const struct vdso_image *image = current->mm->context.vdso_image;
  76
  77         if (image->size != new_size)
  78                 return -EINVAL;
  79
  80         if (WARN_ON_ONCE(current->mm != new_vma->vm_mm))
  81                 return -EFAULT;
  82
  83         vdso_fix_landing(image, new_vma);
  84         current->mm->context.vdso = (void __user *)new_vma->vm_start;
  85
  86         return 0;
  87 }
  88
  89 static int vvar_fault(const struct vm_special_mapping *sm,
  90                       struct vm_area_struct *vma, struct vm_fault *vmf)
  91 {
  92         const struct vdso_image *image = vma->vm_mm->context.vdso_image;
  93         long sym_offset;
  94         int ret = -EFAULT;
  95
  96         if (!image)
  97                 return VM_FAULT_SIGBUS;
  98
  99         sym_offset = (long)(vmf->pgoff << PAGE_SHIFT) +
 100                 image->sym_vvar_start;
 101
 102         /*
 103          * Sanity check: a symbol offset of zero means that the page
 104          * does not exist for this vdso image, not that the page is at
 105          * offset zero relative to the text mapping.  This should be
 106          * impossible here, because sym_offset should only be zero for
 107          * the page past the end of the vvar mapping.
 108          */
 109         if (sym_offset == 0)
 110                 return VM_FAULT_SIGBUS;
 111
 112         if (sym_offset == image->sym_vvar_page) {
 113                 ret = vm_insert_pfn(vma, vmf->address,
 114                                     __pa_symbol(&__vvar_page) >> PAGE_SHIFT);
 115         } else if (sym_offset == image->sym_pvclock_page) {
 116                 struct pvclock_vsyscall_time_info *pvti =
 117                         pvclock_pvti_cpu0_va();
 118                 if (pvti && vclock_was_used(VCLOCK_PVCLOCK)) {
 119                         ret = vm_insert_pfn(
 120                                 vma,
 121                                 vmf->address,
 122                                 __pa(pvti) >> PAGE_SHIFT);
 123                 }
 124         }
 125
 126         if (ret == 0 || ret == -EBUSY)
 127                 return VM_FAULT_NOPAGE;
 128
 129         return VM_FAULT_SIGBUS;
 130 }
 131
 132 static const struct vm_special_mapping vdso_mapping = {
 133         .name = "[vdso]",
 134         .fault = vdso_fault,
 135         .mremap = vdso_mremap,
 136 };
 137 static const struct vm_special_mapping vvar_mapping = {
 138         .name = "[vvar]",
 139         .fault = vvar_fault,
 140 };
 141
 142 /*
 143  * Add vdso and vvar mappings to current process.
 144  * @image          - blob to map
 145  * @addr           - request a specific address (zero to map at free addr)
 146  */
 147 static int map_vdso(const struct vdso_image *image, unsigned long addr)
 148 {
 149         struct mm_struct *mm = current->mm;
 150         struct vm_area_struct *vma;
 151         unsigned long text_start;
 152         int ret = 0;
 153
 154         if (down_write_killable(&mm->mmap_sem))
 155                 return -EINTR;
 156
 157         addr = get_unmapped_area(NULL, addr,
 158                                  image->size - image->sym_vvar_start, 0, 0);
 159         if (IS_ERR_VALUE(addr)) {
 160                 ret = addr;
 161                 goto up_fail;
 162         }
 163
 164         text_start = addr - image->sym_vvar_start;
 165
 166         /*
 167          * MAYWRITE to allow gdb to COW and set breakpoints
 168          */
 169         vma = _install_special_mapping(mm,
 170                                        text_start,
 171                                        image->size,
 172                                        VM_READ|VM_EXEC|
 173                                        VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
 174                                        &vdso_mapping);
 175
 176         if (IS_ERR(vma)) {
 177                 ret = PTR_ERR(vma);
 178                 goto up_fail;
 179         }
 180
 181         vma = _install_special_mapping(mm,
 182                                        addr,
 183                                        -image->sym_vvar_start,
 184                                        VM_READ|VM_MAYREAD|VM_IO|VM_DONTDUMP|
 185                                        VM_PFNMAP,
 186                                        &vvar_mapping);
 187
 188         if (IS_ERR(vma)) {
 189                 ret = PTR_ERR(vma);
 190                 do_munmap(mm, text_start, image->size, NULL);
 191         } else {
 192                 current->mm->context.vdso = (void __user *)text_start;
 193                 current->mm->context.vdso_image = image;
 194         }
 195
 196 up_fail:
 197         up_write(&mm->mmap_sem);
 198         return ret;
 199 }
 200
 201 #ifdef CONFIG_X86_64
 202 /*
 203  * Put the vdso above the (randomized) stack with another randomized
 204  * offset.  This way there is no hole in the middle of address space.
 205  * To save memory make sure it is still in the same PTE as the stack
 206  * top.  This doesn't give that many random bits.
 207  *
 208  * Note that this algorithm is imperfect: the distribution of the vdso
 209  * start address within a PMD is biased toward the end.
 210  *
 211  * Only used for the 64-bit and x32 vdsos.
 212  */
 213 static unsigned long vdso_addr(unsigned long start, unsigned len)
 214 {
 215         unsigned long addr, end;
 216         unsigned offset;
 217
 218         /*
 219          * Round up the start address.  It can start out unaligned as a result
 220          * of stack start randomization.
 221          */
 222         start = PAGE_ALIGN(start);
 223
 224         /* Round the lowest possible end address up to a PMD boundary. */
 225         end = (start + len + PMD_SIZE - 1) & PMD_MASK;
 226         if (end >= TASK_SIZE_MAX)
 227                 end = TASK_SIZE_MAX;
 228         end -= len;
 229
 230         if (end > start) {
 231                 offset = get_random_int() % (((end - start) >> PAGE_SHIFT) + 1);
 232                 addr = start + (offset << PAGE_SHIFT);
 233         } else {
 234                 addr = start;
 235         }
 236
 237         /*
 238          * Forcibly align the final address in case we have a hardware
 239          * issue that requires alignment for performance reasons.
 240          */
 241         addr = align_vdso_addr(addr);
 242
 243         return addr;
 244 }
 245
 246 static int map_vdso_randomized(const struct vdso_image *image)
 247 {
 248         unsigned long addr = vdso_addr(current->mm->start_stack, image->size-image->sym_vvar_start);
 249
 250         return map_vdso(image, addr);
 251 }
 252 #endif
 253
 254 int map_vdso_once(const struct vdso_image *image, unsigned long addr)
 255 {
 256         struct mm_struct *mm = current->mm;
 257         struct vm_area_struct *vma;
 258
 259         down_write(&mm->mmap_sem);
 260         /*
 261          * Check if we have already mapped vdso blob - fail to prevent
 262          * abusing from userspace install_speciall_mapping, which may
 263          * not do accounting and rlimit right.
 264          * We could search vma near context.vdso, but it's a slowpath,
 265          * so let's explicitely check all VMAs to be completely sure.
 266          */
 267         for (vma = mm->mmap; vma; vma = vma->vm_next) {
 268                 if (vma_is_special_mapping(vma, &vdso_mapping) ||
 269                                 vma_is_special_mapping(vma, &vvar_mapping)) {
 270                         up_write(&mm->mmap_sem);
 271                         return -EEXIST;
 272                 }
 273         }
 274         up_write(&mm->mmap_sem);
 275
 276         return map_vdso(image, addr);
 277 }
 278
 279 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
 280 static int load_vdso32(void)
 281 {
 282         if (vdso32_enabled != 1)  /* Other values all mean "disabled" */
 283                 return 0;
 284
 285         return map_vdso(&vdso_image_32, 0);
 286 }
 287 #endif
 288
 289 #ifdef CONFIG_X86_64
 290 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 291 {
 292         if (!vdso64_enabled)
 293                 return 0;
 294
 295         return map_vdso_randomized(&vdso_image_64);
 296 }
 297
 298 #ifdef CONFIG_COMPAT
 299 int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
 300                                        int uses_interp)
 301 {
 302 #ifdef CONFIG_X86_X32_ABI
 303         if (test_thread_flag(TIF_X32)) {
 304                 if (!vdso64_enabled)
 305                         return 0;
 306                 return map_vdso_randomized(&vdso_image_x32);
 307         }
 308 #endif
 309 #ifdef CONFIG_IA32_EMULATION
 310         return load_vdso32();
 311 #else
 312         return 0;
 313 #endif
 314 }
 315 #endif
 316 #else
 317 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 318 {
 319         return load_vdso32();
 320 }
 321 #endif
 322
 323 #ifdef CONFIG_X86_64
 324 static __init int vdso_setup(char *s)
 325 {
 326         vdso64_enabled = simple_strtoul(s, NULL, 0);
 327         return 0;
 328 }
 329 __setup("vdso=", vdso_setup);
 330 #endif
 331
 332 #ifdef CONFIG_X86_64
 333 static void vgetcpu_cpu_init(void *arg)
 334 {
 335         int cpu = smp_processor_id();
 336         struct desc_struct d = { };
 337         unsigned long node = 0;
 338 #ifdef CONFIG_NUMA
 339         node = cpu_to_node(cpu);
 340 #endif
 341         if (static_cpu_has(X86_FEATURE_RDTSCP))
 342                 write_rdtscp_aux((node << 12) | cpu);
 343
 344         /*
 345          * Store cpu number in limit so that it can be loaded
 346          * quickly in user space in vgetcpu. (12 bits for the CPU
 347          * and 8 bits for the node)
 348          */
 349         d.limit0 = cpu | ((node & 0xf) << 12);
 350         d.limit = node >> 4;
 351         d.type = 5;             /* RO data, expand down, accessed */
 352         d.dpl = 3;              /* Visible to user code */
 353         d.s = 1;                /* Not a system segment */
 354         d.p = 1;                /* Present */
 355         d.d = 1;                /* 32-bit */
 356
 357         write_gdt_entry(get_cpu_gdt_table(cpu), GDT_ENTRY_PER_CPU, &d, DESCTYPE_S);
 358 }
 359
 360 static int vgetcpu_online(unsigned int cpu)
 361 {
 362         return smp_call_function_single(cpu, vgetcpu_cpu_init, NULL, 1);
 363 }
 364
 365 static int __init init_vdso(void)
 366 {
 367         init_vdso_image(&vdso_image_64);
 368
 369 #ifdef CONFIG_X86_X32_ABI
 370         init_vdso_image(&vdso_image_x32);
 371 #endif
 372
 373         /* notifier priority > KVM */
 374         return cpuhp_setup_state(CPUHP_AP_X86_VDSO_VMA_ONLINE,
 375                                  "x86/vdso/vma:online", vgetcpu_online, NULL);
 376 }
 377 subsys_initcall(init_vdso);
 378 #endif /* CONFIG_X86_64 */