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 ([email protected])
   7  */
   8
   9 #include <linux/init.h>
  10 #include <linux/errno.h>
  11 #include <linux/sched.h>
  12 #include <linux/kernel.h>
  13 #include <linux/mm.h>
  14 #include <linux/smp.h>
  15 #include <linux/stddef.h>
  16 #include <linux/unistd.h>
  17 #include <linux/slab.h>
  18 #include <linux/user.h>
  19 #include <linux/elf.h>
  20 #include <linux/security.h>
  21 #include <linux/memblock.h>
  22 #include <linux/compat.h>
  23 #include <linux/binfmts.h>
  24 #include <vdso/datapage.h>
  25 #include <asm/asm-offsets.h>
  26 #include <asm/processor.h>
  27 #include <asm/mmu.h>
  28 #include <asm/mmu_context.h>
  29 #include <asm/sections.h>
  30 #include <asm/vdso.h>
  31 #include <asm/facility.h>
  32
  33 extern char vdso64_start, vdso64_end;
  34 static void *vdso64_kbase = &vdso64_start;
  35 static unsigned int vdso64_pages;
  36 static struct page **vdso64_pagelist;
  37
  38 /*
  39  * Should the kernel map a VDSO page into processes and pass its
  40  * address down to glibc upon exec()?
  41  */
  42 unsigned int __read_mostly vdso_enabled = 1;
  43
  44 static vm_fault_t vdso_fault(const struct vm_special_mapping *sm,
  45                       struct vm_area_struct *vma, struct vm_fault *vmf)
  46 {
  47         struct page **vdso_pagelist;
  48         unsigned long vdso_pages;
  49
  50         vdso_pagelist = vdso64_pagelist;
  51         vdso_pages = vdso64_pages;
  52
  53         if (vmf->pgoff >= vdso_pages)
  54                 return VM_FAULT_SIGBUS;
  55
  56         vmf->page = vdso_pagelist[vmf->pgoff];
  57         get_page(vmf->page);
  58         return 0;
  59 }
  60
  61 static int vdso_mremap(const struct vm_special_mapping *sm,
  62                        struct vm_area_struct *vma)
  63 {
  64         unsigned long vdso_pages;
  65
  66         vdso_pages = vdso64_pages;
  67
  68         if ((vdso_pages << PAGE_SHIFT) != vma->vm_end - vma->vm_start)
  69                 return -EINVAL;
  70
  71         if (WARN_ON_ONCE(current->mm != vma->vm_mm))
  72                 return -EFAULT;
  73
  74         current->mm->context.vdso_base = vma->vm_start;
  75         return 0;
  76 }
  77
  78 static const struct vm_special_mapping vdso_mapping = {
  79         .name = "[vdso]",
  80         .fault = vdso_fault,
  81         .mremap = vdso_mremap,
  82 };
  83
  84 static int __init vdso_setup(char *str)
  85 {
  86         bool enabled;
  87
  88         if (!kstrtobool(str, &enabled))
  89                 vdso_enabled = enabled;
  90         return 1;
  91 }
  92 __setup("vdso=", vdso_setup);
  93
  94 /*
  95  * The vdso data page
  96  */
  97 static union {
  98         struct vdso_data        data;
  99         u8                      page[PAGE_SIZE];
 100 } vdso_data_store __page_aligned_data;
 101 struct vdso_data *vdso_data = (struct vdso_data *)&vdso_data_store.data;
 102 /*
 103  * Allocate/free per cpu vdso data.
 104  */
 105 #define SEGMENT_ORDER   2
 106
 107 int vdso_alloc_per_cpu(struct lowcore *lowcore)
 108 {
 109         unsigned long segment_table, page_table, page_frame;
 110         struct vdso_per_cpu_data *vd;
 111
 112         segment_table = __get_free_pages(GFP_KERNEL, SEGMENT_ORDER);
 113         page_table = get_zeroed_page(GFP_KERNEL);
 114         page_frame = get_zeroed_page(GFP_KERNEL);
 115         if (!segment_table || !page_table || !page_frame)
 116                 goto out;
 117         arch_set_page_dat(virt_to_page(segment_table), SEGMENT_ORDER);
 118         arch_set_page_dat(virt_to_page(page_table), 0);
 119
 120         /* Initialize per-cpu vdso data page */
 121         vd = (struct vdso_per_cpu_data *) page_frame;
 122         vd->cpu_nr = lowcore->cpu_nr;
 123         vd->node_id = cpu_to_node(vd->cpu_nr);
 124
 125         /* Set up page table for the vdso address space */
 126         memset64((u64 *)segment_table, _SEGMENT_ENTRY_EMPTY, _CRST_ENTRIES);
 127         memset64((u64 *)page_table, _PAGE_INVALID, PTRS_PER_PTE);
 128
 129         *(unsigned long *) segment_table = _SEGMENT_ENTRY + page_table;
 130         *(unsigned long *) page_table = _PAGE_PROTECT + page_frame;
 131
 132         lowcore->vdso_asce = segment_table +
 133                 _ASCE_TABLE_LENGTH + _ASCE_USER_BITS + _ASCE_TYPE_SEGMENT;
 134         lowcore->vdso_per_cpu_data = page_frame;
 135
 136         return 0;
 137
 138 out:
 139         free_page(page_frame);
 140         free_page(page_table);
 141         free_pages(segment_table, SEGMENT_ORDER);
 142         return -ENOMEM;
 143 }
 144
 145 void vdso_free_per_cpu(struct lowcore *lowcore)
 146 {
 147         unsigned long segment_table, page_table, page_frame;
 148
 149         segment_table = lowcore->vdso_asce & PAGE_MASK;
 150         page_table = *(unsigned long *) segment_table;
 151         page_frame = *(unsigned long *) page_table;
 152
 153         free_page(page_frame);
 154         free_page(page_table);
 155         free_pages(segment_table, SEGMENT_ORDER);
 156 }
 157
 158 /*
 159  * This is called from binfmt_elf, we create the special vma for the
 160  * vDSO and insert it into the mm struct tree
 161  */
 162 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 163 {
 164         struct mm_struct *mm = current->mm;
 165         struct vm_area_struct *vma;
 166         unsigned long vdso_pages;
 167         unsigned long vdso_base;
 168         int rc;
 169
 170         if (!vdso_enabled)
 171                 return 0;
 172
 173         if (is_compat_task())
 174                 return 0;
 175
 176         vdso_pages = vdso64_pages;
 177         /*
 178          * vDSO has a problem and was disabled, just don't "enable" it for
 179          * the process
 180          */
 181         if (vdso_pages == 0)
 182                 return 0;
 183
 184         /*
 185          * pick a base address for the vDSO in process space. We try to put
 186          * it at vdso_base which is the "natural" base for it, but we might
 187          * fail and end up putting it elsewhere.
 188          */
 189         if (mmap_write_lock_killable(mm))
 190                 return -EINTR;
 191         vdso_base = get_unmapped_area(NULL, 0, vdso_pages << PAGE_SHIFT, 0, 0);
 192         if (IS_ERR_VALUE(vdso_base)) {
 193                 rc = vdso_base;
 194                 goto out_up;
 195         }
 196
 197         /*
 198          * our vma flags don't have VM_WRITE so by default, the process
 199          * isn't allowed to write those pages.
 200          * gdb can break that with ptrace interface, and thus trigger COW
 201          * on those pages but it's then your responsibility to never do that
 202          * on the "data" page of the vDSO or you'll stop getting kernel
 203          * updates and your nice userland gettimeofday will be totally dead.
 204          * It's fine to use that for setting breakpoints in the vDSO code
 205          * pages though.
 206          */
 207         vma = _install_special_mapping(mm, vdso_base, vdso_pages << PAGE_SHIFT,
 208                                        VM_READ|VM_EXEC|
 209                                        VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
 210                                        &vdso_mapping);
 211         if (IS_ERR(vma)) {
 212                 rc = PTR_ERR(vma);
 213                 goto out_up;
 214         }
 215
 216         current->mm->context.vdso_base = vdso_base;
 217         rc = 0;
 218
 219 out_up:
 220         mmap_write_unlock(mm);
 221         return rc;
 222 }
 223
 224 static int __init vdso_init(void)
 225 {
 226         int i;
 227
 228         /* Calculate the size of the 64 bit vDSO */
 229         vdso64_pages = ((&vdso64_end - &vdso64_start
 230                          + PAGE_SIZE - 1) >> PAGE_SHIFT) + 1;
 231
 232         /* Make sure pages are in the correct state */
 233         vdso64_pagelist = kcalloc(vdso64_pages + 1, sizeof(struct page *),
 234                                   GFP_KERNEL);
 235         BUG_ON(vdso64_pagelist == NULL);
 236         for (i = 0; i < vdso64_pages - 1; i++) {
 237                 struct page *pg = virt_to_page(vdso64_kbase + i*PAGE_SIZE);
 238                 get_page(pg);
 239                 vdso64_pagelist[i] = pg;
 240         }
 241         vdso64_pagelist[vdso64_pages - 1] = virt_to_page(vdso_data);
 242         vdso64_pagelist[vdso64_pages] = NULL;
 243         if (vdso_alloc_per_cpu(&S390_lowcore))
 244                 BUG();
 245
 246         get_page(virt_to_page(vdso_data));
 247
 248         return 0;
 249 }
 250 early_initcall(vdso_init);