arch/s390/kernel/vdso.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * vdso setup for s390
   4  *
   5  *  Copyright IBM Corp. 2008
   6  *  Author(s): Martin Schwidefsky (schwidefsky@de.ibm.com)
   7  */
   8
   9 #include <linux/binfmts.h>
  10 #include <linux/compat.h>
  11 #include <linux/elf.h>
  12 #include <linux/errno.h>
  13 #include <linux/init.h>
  14 #include <linux/kernel.h>
  15 #include <linux/mm.h>
  16 #include <linux/slab.h>
  17 #include <linux/smp.h>
  18 #include <linux/time_namespace.h>
  19 #include <linux/random.h>
  20 #include <vdso/datapage.h>
  21 #include <asm/vdso.h>
  22
  23 extern char vdso64_start[], vdso64_end[];
  24 extern char vdso32_start[], vdso32_end[];
  25
  26 static struct vm_special_mapping vvar_mapping;
  27
  28 static union {
  29         struct vdso_data        data[CS_BASES];
  30         u8                      page[PAGE_SIZE];
  31 } vdso_data_store __page_aligned_data;
  32
  33 struct vdso_data *vdso_data = vdso_data_store.data;
  34
  35 enum vvar_pages {
  36         VVAR_DATA_PAGE_OFFSET,
  37         VVAR_TIMENS_PAGE_OFFSET,
  38         VVAR_NR_PAGES,
  39 };
  40
  41 #ifdef CONFIG_TIME_NS
  42 struct vdso_data *arch_get_vdso_data(void *vvar_page)
  43 {
  44         return (struct vdso_data *)(vvar_page);
  45 }
  46
  47 static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
  48 {
  49         if (likely(vma->vm_mm == current->mm))
  50                 return current->nsproxy->time_ns->vvar_page;
  51         /*
  52          * VM_PFNMAP | VM_IO protect .fault() handler from being called
  53          * through interfaces like /proc/$pid/mem or
  54          * process_vm_{readv,writev}() as long as there's no .access()
  55          * in special_mapping_vmops().
  56          * For more details check_vma_flags() and __access_remote_vm()
  57          */
  58         WARN(1, "vvar_page accessed remotely");
  59         return NULL;
  60 }
  61
  62 /*
  63  * The VVAR page layout depends on whether a task belongs to the root or
  64  * non-root time namespace. Whenever a task changes its namespace, the VVAR
  65  * page tables are cleared and then they will be re-faulted with a
  66  * corresponding layout.
  67  * See also the comment near timens_setup_vdso_data() for details.
  68  */
  69 int vdso_join_timens(struct task_struct *task, struct time_namespace *ns)
  70 {
  71         struct mm_struct *mm = task->mm;
  72         VMA_ITERATOR(vmi, mm, 0);
  73         struct vm_area_struct *vma;
  74
  75         mmap_read_lock(mm);
  76         for_each_vma(vmi, vma) {
  77                 unsigned long size = vma->vm_end - vma->vm_start;
  78
  79                 if (!vma_is_special_mapping(vma, &vvar_mapping))
  80                         continue;
  81                 zap_page_range(vma, vma->vm_start, size);
  82                 break;
  83         }
  84         mmap_read_unlock(mm);
  85         return 0;
  86 }
  87 #else
  88 static inline struct page *find_timens_vvar_page(struct vm_area_struct *vma)
  89 {
  90         return NULL;
  91 }
  92 #endif
  93
  94 static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
  95                              struct vm_area_struct *vma, struct vm_fault *vmf)
  96 {
  97         struct page *timens_page = find_timens_vvar_page(vma);
  98         unsigned long addr, pfn;
  99         vm_fault_t err;
 100
 101         switch (vmf->pgoff) {
 102         case VVAR_DATA_PAGE_OFFSET:
 103                 pfn = virt_to_pfn(vdso_data);
 104                 if (timens_page) {
 105                         /*
 106                          * Fault in VVAR page too, since it will be accessed
 107                          * to get clock data anyway.
 108                          */
 109                         addr = vmf->address + VVAR_TIMENS_PAGE_OFFSET * PAGE_SIZE;
 110                         err = vmf_insert_pfn(vma, addr, pfn);
 111                         if (unlikely(err & VM_FAULT_ERROR))
 112                                 return err;
 113                         pfn = page_to_pfn(timens_page);
 114                 }
 115                 break;
 116 #ifdef CONFIG_TIME_NS
 117         case VVAR_TIMENS_PAGE_OFFSET:
 118                 /*
 119                  * If a task belongs to a time namespace then a namespace
 120                  * specific VVAR is mapped with the VVAR_DATA_PAGE_OFFSET and
 121                  * the real VVAR page is mapped with the VVAR_TIMENS_PAGE_OFFSET
 122                  * offset.
 123                  * See also the comment near timens_setup_vdso_data().
 124                  */
 125                 if (!timens_page)
 126                         return VM_FAULT_SIGBUS;
 127                 pfn = virt_to_pfn(vdso_data);
 128                 break;
 129 #endif /* CONFIG_TIME_NS */
 130         default:
 131                 return VM_FAULT_SIGBUS;
 132         }
 133         return vmf_insert_pfn(vma, vmf->address, pfn);
 134 }
 135
 136 static int vdso_mremap(const struct vm_special_mapping *sm,
 137                        struct vm_area_struct *vma)
 138 {
 139         current->mm->context.vdso_base = vma->vm_start;
 140         return 0;
 141 }
 142
 143 static struct vm_special_mapping vvar_mapping = {
 144         .name = "[vvar]",
 145         .fault = vvar_fault,
 146 };
 147
 148 static struct vm_special_mapping vdso64_mapping = {
 149         .name = "[vdso]",
 150         .mremap = vdso_mremap,
 151 };
 152
 153 static struct vm_special_mapping vdso32_mapping = {
 154         .name = "[vdso]",
 155         .mremap = vdso_mremap,
 156 };
 157
 158 int vdso_getcpu_init(void)
 159 {
 160         set_tod_programmable_field(smp_processor_id());
 161         return 0;
 162 }
 163 early_initcall(vdso_getcpu_init); /* Must be called before SMP init */
 164
 165 static int map_vdso(unsigned long addr, unsigned long vdso_mapping_len)
 166 {
 167         unsigned long vvar_start, vdso_text_start, vdso_text_len;
 168         struct vm_special_mapping *vdso_mapping;
 169         struct mm_struct *mm = current->mm;
 170         struct vm_area_struct *vma;
 171         int rc;
 172
 173         BUILD_BUG_ON(VVAR_NR_PAGES != __VVAR_PAGES);
 174         if (mmap_write_lock_killable(mm))
 175                 return -EINTR;
 176
 177         if (is_compat_task()) {
 178                 vdso_text_len = vdso32_end - vdso32_start;
 179                 vdso_mapping = &vdso32_mapping;
 180         } else {
 181                 vdso_text_len = vdso64_end - vdso64_start;
 182                 vdso_mapping = &vdso64_mapping;
 183         }
 184         vvar_start = get_unmapped_area(NULL, addr, vdso_mapping_len, 0, 0);
 185         rc = vvar_start;
 186         if (IS_ERR_VALUE(vvar_start))
 187                 goto out;
 188         vma = _install_special_mapping(mm, vvar_start, VVAR_NR_PAGES*PAGE_SIZE,
 189                                        VM_READ|VM_MAYREAD|VM_IO|VM_DONTDUMP|
 190                                        VM_PFNMAP,
 191                                        &vvar_mapping);
 192         rc = PTR_ERR(vma);
 193         if (IS_ERR(vma))
 194                 goto out;
 195         vdso_text_start = vvar_start + VVAR_NR_PAGES * PAGE_SIZE;
 196         /* VM_MAYWRITE for COW so gdb can set breakpoints */
 197         vma = _install_special_mapping(mm, vdso_text_start, vdso_text_len,
 198                                        VM_READ|VM_EXEC|
 199                                        VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
 200                                        vdso_mapping);
 201         if (IS_ERR(vma)) {
 202                 do_munmap(mm, vvar_start, PAGE_SIZE, NULL);
 203                 rc = PTR_ERR(vma);
 204         } else {
 205                 current->mm->context.vdso_base = vdso_text_start;
 206                 rc = 0;
 207         }
 208 out:
 209         mmap_write_unlock(mm);
 210         return rc;
 211 }
 212
 213 static unsigned long vdso_addr(unsigned long start, unsigned long len)
 214 {
 215         unsigned long addr, end, 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 >= VDSO_BASE)
 226                 end = VDSO_BASE;
 227         end -= len;
 228
 229         if (end > start) {
 230                 offset = prandom_u32_max(((end - start) >> PAGE_SHIFT) + 1);
 231                 addr = start + (offset << PAGE_SHIFT);
 232         } else {
 233                 addr = start;
 234         }
 235         return addr;
 236 }
 237
 238 unsigned long vdso_size(void)
 239 {
 240         unsigned long size = VVAR_NR_PAGES * PAGE_SIZE;
 241
 242         if (is_compat_task())
 243                 size += vdso32_end - vdso32_start;
 244         else
 245                 size += vdso64_end - vdso64_start;
 246         return PAGE_ALIGN(size);
 247 }
 248
 249 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 250 {
 251         unsigned long addr = VDSO_BASE;
 252         unsigned long size = vdso_size();
 253
 254         if (current->flags & PF_RANDOMIZE)
 255                 addr = vdso_addr(current->mm->start_stack + PAGE_SIZE, size);
 256         return map_vdso(addr, size);
 257 }
 258
 259 static struct page ** __init vdso_setup_pages(void *start, void *end)
 260 {
 261         int pages = (end - start) >> PAGE_SHIFT;
 262         struct page **pagelist;
 263         int i;
 264
 265         pagelist = kcalloc(pages + 1, sizeof(struct page *), GFP_KERNEL);
 266         if (!pagelist)
 267                 panic("%s: Cannot allocate page list for VDSO", __func__);
 268         for (i = 0; i < pages; i++)
 269                 pagelist[i] = virt_to_page(start + i * PAGE_SIZE);
 270         return pagelist;
 271 }
 272
 273 static int __init vdso_init(void)
 274 {
 275         vdso64_mapping.pages = vdso_setup_pages(vdso64_start, vdso64_end);
 276         if (IS_ENABLED(CONFIG_COMPAT))
 277                 vdso32_mapping.pages = vdso_setup_pages(vdso32_start, vdso32_end);
 278         return 0;
 279 }
 280 arch_initcall(vdso_init);