arch/x86/entry/vdso/vma.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright 2007 Andi Kleen, SUSE Labs.
   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 #include <asm/mshyperv.h>
  26
  27 #if defined(CONFIG_X86_64)
  28 unsigned int __read_mostly vdso64_enabled = 1;
  29 #endif
  30
  31 void __init init_vdso_image(const struct vdso_image *image)
  32 {
  33         BUG_ON(image->size % PAGE_SIZE != 0);
  34
  35         apply_alternatives((struct alt_instr *)(image->data + image->alt),
  36                            (struct alt_instr *)(image->data + image->alt +
  37                                                 image->alt_len));
  38 }
  39
  40 struct linux_binprm;
  41
  42 static vm_fault_t vdso_fault(const struct vm_special_mapping *sm,
  43                       struct vm_area_struct *vma, struct vm_fault *vmf)
  44 {
  45         const struct vdso_image *image = vma->vm_mm->context.vdso_image;
  46
  47         if (!image || (vmf->pgoff << PAGE_SHIFT) >= image->size)
  48                 return VM_FAULT_SIGBUS;
  49
  50         vmf->page = virt_to_page(image->data + (vmf->pgoff << PAGE_SHIFT));
  51         get_page(vmf->page);
  52         return 0;
  53 }
  54
  55 static void vdso_fix_landing(const struct vdso_image *image,
  56                 struct vm_area_struct *new_vma)
  57 {
  58 #if defined CONFIG_X86_32 || defined CONFIG_IA32_EMULATION
  59         if (in_ia32_syscall() && image == &vdso_image_32) {
  60                 struct pt_regs *regs = current_pt_regs();
  61                 unsigned long vdso_land = image->sym_int80_landing_pad;
  62                 unsigned long old_land_addr = vdso_land +
  63                         (unsigned long)current->mm->context.vdso;
  64
  65                 /* Fixing userspace landing - look at do_fast_syscall_32 */
  66                 if (regs->ip == old_land_addr)
  67                         regs->ip = new_vma->vm_start + vdso_land;
  68         }
  69 #endif
  70 }
  71
  72 static int vdso_mremap(const struct vm_special_mapping *sm,
  73                 struct vm_area_struct *new_vma)
  74 {
  75         unsigned long new_size = new_vma->vm_end - new_vma->vm_start;
  76         const struct vdso_image *image = current->mm->context.vdso_image;
  77
  78         if (image->size != new_size)
  79                 return -EINVAL;
  80
  81         vdso_fix_landing(image, new_vma);
  82         current->mm->context.vdso = (void __user *)new_vma->vm_start;
  83
  84         return 0;
  85 }
  86
  87 static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
  88                       struct vm_area_struct *vma, struct vm_fault *vmf)
  89 {
  90         const struct vdso_image *image = vma->vm_mm->context.vdso_image;
  91         long sym_offset;
  92
  93         if (!image)
  94                 return VM_FAULT_SIGBUS;
  95
  96         sym_offset = (long)(vmf->pgoff << PAGE_SHIFT) +
  97                 image->sym_vvar_start;
  98
  99         /*
 100          * Sanity check: a symbol offset of zero means that the page
 101          * does not exist for this vdso image, not that the page is at
 102          * offset zero relative to the text mapping.  This should be
 103          * impossible here, because sym_offset should only be zero for
 104          * the page past the end of the vvar mapping.
 105          */
 106         if (sym_offset == 0)
 107                 return VM_FAULT_SIGBUS;
 108
 109         if (sym_offset == image->sym_vvar_page) {
 110                 return vmf_insert_pfn(vma, vmf->address,
 111                                 __pa_symbol(&__vvar_page) >> PAGE_SHIFT);
 112         } else if (sym_offset == image->sym_pvclock_page) {
 113                 struct pvclock_vsyscall_time_info *pvti =
 114                         pvclock_get_pvti_cpu0_va();
 115                 if (pvti && vclock_was_used(VCLOCK_PVCLOCK)) {
 116                         return vmf_insert_pfn_prot(vma, vmf->address,
 117                                         __pa(pvti) >> PAGE_SHIFT,
 118                                         pgprot_decrypted(vma->vm_page_prot));
 119                 }
 120         } else if (sym_offset == image->sym_hvclock_page) {
 121                 struct ms_hyperv_tsc_page *tsc_pg = hv_get_tsc_page();
 122
 123                 if (tsc_pg && vclock_was_used(VCLOCK_HVCLOCK))
 124                         return vmf_insert_pfn(vma, vmf->address,
 125                                         vmalloc_to_pfn(tsc_pg));
 126         }
 127
 128         return VM_FAULT_SIGBUS;
 129 }
 130
 131 static const struct vm_special_mapping vdso_mapping = {
 132         .name = "[vdso]",
 133         .fault = vdso_fault,
 134         .mremap = vdso_mremap,
 135 };
 136 static const struct vm_special_mapping vvar_mapping = {
 137         .name = "[vvar]",
 138         .fault = vvar_fault,
 139 };
 140
 141 /*
 142  * Add vdso and vvar mappings to current process.
 143  * @image          - blob to map
 144  * @addr           - request a specific address (zero to map at free addr)
 145  */
 146 static int map_vdso(const struct vdso_image *image, unsigned long addr)
 147 {
 148         struct mm_struct *mm = current->mm;
 149         struct vm_area_struct *vma;
 150         unsigned long text_start;
 151         int ret = 0;
 152
 153         if (down_write_killable(&mm->mmap_sem))
 154                 return -EINTR;
 155
 156         addr = get_unmapped_area(NULL, addr,
 157                                  image->size - image->sym_vvar_start, 0, 0);
 158         if (IS_ERR_VALUE(addr)) {
 159                 ret = addr;
 160                 goto up_fail;
 161         }
 162
 163         text_start = addr - image->sym_vvar_start;
 164
 165         /*
 166          * MAYWRITE to allow gdb to COW and set breakpoints
 167          */
 168         vma = _install_special_mapping(mm,
 169                                        text_start,
 170                                        image->size,
 171                                        VM_READ|VM_EXEC|
 172                                        VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
 173                                        &vdso_mapping);
 174
 175         if (IS_ERR(vma)) {
 176                 ret = PTR_ERR(vma);
 177                 goto up_fail;
 178         }
 179
 180         vma = _install_special_mapping(mm,
 181                                        addr,
 182                                        -image->sym_vvar_start,
 183                                        VM_READ|VM_MAYREAD|VM_IO|VM_DONTDUMP|
 184                                        VM_PFNMAP,
 185                                        &vvar_mapping);
 186
 187         if (IS_ERR(vma)) {
 188                 ret = PTR_ERR(vma);
 189                 do_munmap(mm, text_start, image->size, NULL);
 190         } else {
 191                 current->mm->context.vdso = (void __user *)text_start;
 192                 current->mm->context.vdso_image = image;
 193         }
 194
 195 up_fail:
 196         up_write(&mm->mmap_sem);
 197         return ret;
 198 }
 199
 200 #ifdef CONFIG_X86_64
 201 /*
 202  * Put the vdso above the (randomized) stack with another randomized
 203  * offset.  This way there is no hole in the middle of address space.
 204  * To save memory make sure it is still in the same PTE as the stack
 205  * top.  This doesn't give that many random bits.
 206  *
 207  * Note that this algorithm is imperfect: the distribution of the vdso
 208  * start address within a PMD is biased toward the end.
 209  *
 210  * Only used for the 64-bit and x32 vdsos.
 211  */
 212 static unsigned long vdso_addr(unsigned long start, unsigned len)
 213 {
 214         unsigned long addr, end;
 215         unsigned offset;
 216
 217         /*
 218          * Round up the start address.  It can start out unaligned as a result
 219          * of stack start randomization.
 220          */
 221         start = PAGE_ALIGN(start);
 222
 223         /* Round the lowest possible end address up to a PMD boundary. */
 224         end = (start + len + PMD_SIZE - 1) & PMD_MASK;
 225         if (end >= TASK_SIZE_MAX)
 226                 end = TASK_SIZE_MAX;
 227         end -= len;
 228
 229         if (end > start) {
 230                 offset = get_random_int() % (((end - start) >> PAGE_SHIFT) + 1);
 231                 addr = start + (offset << PAGE_SHIFT);
 232         } else {
 233                 addr = start;
 234         }
 235
 236         /*
 237          * Forcibly align the final address in case we have a hardware
 238          * issue that requires alignment for performance reasons.
 239          */
 240         addr = align_vdso_addr(addr);
 241
 242         return addr;
 243 }
 244
 245 static int map_vdso_randomized(const struct vdso_image *image)
 246 {
 247         unsigned long addr = vdso_addr(current->mm->start_stack, image->size-image->sym_vvar_start);
 248
 249         return map_vdso(image, addr);
 250 }
 251 #endif
 252
 253 int map_vdso_once(const struct vdso_image *image, unsigned long addr)
 254 {
 255         struct mm_struct *mm = current->mm;
 256         struct vm_area_struct *vma;
 257
 258         down_write(&mm->mmap_sem);
 259         /*
 260          * Check if we have already mapped vdso blob - fail to prevent
 261          * abusing from userspace install_speciall_mapping, which may
 262          * not do accounting and rlimit right.
 263          * We could search vma near context.vdso, but it's a slowpath,
 264          * so let's explicitly check all VMAs to be completely sure.
 265          */
 266         for (vma = mm->mmap; vma; vma = vma->vm_next) {
 267                 if (vma_is_special_mapping(vma, &vdso_mapping) ||
 268                                 vma_is_special_mapping(vma, &vvar_mapping)) {
 269                         up_write(&mm->mmap_sem);
 270                         return -EEXIST;
 271                 }
 272         }
 273         up_write(&mm->mmap_sem);
 274
 275         return map_vdso(image, addr);
 276 }
 277
 278 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
 279 static int load_vdso32(void)
 280 {
 281         if (vdso32_enabled != 1)  /* Other values all mean "disabled" */
 282                 return 0;
 283
 284         return map_vdso(&vdso_image_32, 0);
 285 }
 286 #endif
 287
 288 #ifdef CONFIG_X86_64
 289 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 290 {
 291         if (!vdso64_enabled)
 292                 return 0;
 293
 294         return map_vdso_randomized(&vdso_image_64);
 295 }
 296
 297 #ifdef CONFIG_COMPAT
 298 int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
 299                                        int uses_interp)
 300 {
 301 #ifdef CONFIG_X86_X32_ABI
 302         if (test_thread_flag(TIF_X32)) {
 303                 if (!vdso64_enabled)
 304                         return 0;
 305                 return map_vdso_randomized(&vdso_image_x32);
 306         }
 307 #endif
 308 #ifdef CONFIG_IA32_EMULATION
 309         return load_vdso32();
 310 #else
 311         return 0;
 312 #endif
 313 }
 314 #endif
 315 #else
 316 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 317 {
 318         return load_vdso32();
 319 }
 320 #endif
 321
 322 #ifdef CONFIG_X86_64
 323 static __init int vdso_setup(char *s)
 324 {
 325         vdso64_enabled = simple_strtoul(s, NULL, 0);
 326         return 0;
 327 }
 328 __setup("vdso=", vdso_setup);
 329
 330 static int __init init_vdso(void)
 331 {
 332         init_vdso_image(&vdso_image_64);
 333
 334 #ifdef CONFIG_X86_X32_ABI
 335         init_vdso_image(&vdso_image_x32);
 336 #endif
 337
 338         return 0;
 339 }
 340 subsys_initcall(init_vdso);
 341 #endif /* CONFIG_X86_64 */