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/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 #include <asm/timex.h>
  33
  34 extern char vdso64_start, vdso64_end;
  35 static void *vdso64_kbase = &vdso64_start;
  36 static unsigned int vdso64_pages;
  37 static struct page **vdso64_pagelist;
  38
  39 /*
  40  * Should the kernel map a VDSO page into processes and pass its
  41  * address down to glibc upon exec()?
  42  */
  43 unsigned int __read_mostly vdso_enabled = 1;
  44
  45 static vm_fault_t vdso_fault(const struct vm_special_mapping *sm,
  46                       struct vm_area_struct *vma, struct vm_fault *vmf)
  47 {
  48         struct page **vdso_pagelist;
  49         unsigned long vdso_pages;
  50
  51         vdso_pagelist = vdso64_pagelist;
  52         vdso_pages = vdso64_pages;
  53
  54         if (vmf->pgoff >= vdso_pages)
  55                 return VM_FAULT_SIGBUS;
  56
  57         vmf->page = vdso_pagelist[vmf->pgoff];
  58         get_page(vmf->page);
  59         return 0;
  60 }
  61
  62 static int vdso_mremap(const struct vm_special_mapping *sm,
  63                        struct vm_area_struct *vma)
  64 {
  65         current->mm->context.vdso_base = vma->vm_start;
  66
  67         return 0;
  68 }
  69
  70 static const struct vm_special_mapping vdso_mapping = {
  71         .name = "[vdso]",
  72         .fault = vdso_fault,
  73         .mremap = vdso_mremap,
  74 };
  75
  76 static int __init vdso_setup(char *str)
  77 {
  78         bool enabled;
  79
  80         if (!kstrtobool(str, &enabled))
  81                 vdso_enabled = enabled;
  82         return 1;
  83 }
  84 __setup("vdso=", vdso_setup);
  85
  86 /*
  87  * The vdso data page
  88  */
  89 static union {
  90         struct vdso_data        data;
  91         u8                      page[PAGE_SIZE];
  92 } vdso_data_store __page_aligned_data;
  93 struct vdso_data *vdso_data = (struct vdso_data *)&vdso_data_store.data;
  94
  95 void vdso_getcpu_init(void)
  96 {
  97         set_tod_programmable_field(smp_processor_id());
  98 }
  99
 100 /*
 101  * This is called from binfmt_elf, we create the special vma for the
 102  * vDSO and insert it into the mm struct tree
 103  */
 104 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 105 {
 106         struct mm_struct *mm = current->mm;
 107         struct vm_area_struct *vma;
 108         unsigned long vdso_pages;
 109         unsigned long vdso_base;
 110         int rc;
 111
 112         if (!vdso_enabled)
 113                 return 0;
 114
 115         if (is_compat_task())
 116                 return 0;
 117
 118         vdso_pages = vdso64_pages;
 119         /*
 120          * vDSO has a problem and was disabled, just don't "enable" it for
 121          * the process
 122          */
 123         if (vdso_pages == 0)
 124                 return 0;
 125
 126         /*
 127          * pick a base address for the vDSO in process space. We try to put
 128          * it at vdso_base which is the "natural" base for it, but we might
 129          * fail and end up putting it elsewhere.
 130          */
 131         if (mmap_write_lock_killable(mm))
 132                 return -EINTR;
 133         vdso_base = get_unmapped_area(NULL, 0, vdso_pages << PAGE_SHIFT, 0, 0);
 134         if (IS_ERR_VALUE(vdso_base)) {
 135                 rc = vdso_base;
 136                 goto out_up;
 137         }
 138
 139         /*
 140          * our vma flags don't have VM_WRITE so by default, the process
 141          * isn't allowed to write those pages.
 142          * gdb can break that with ptrace interface, and thus trigger COW
 143          * on those pages but it's then your responsibility to never do that
 144          * on the "data" page of the vDSO or you'll stop getting kernel
 145          * updates and your nice userland gettimeofday will be totally dead.
 146          * It's fine to use that for setting breakpoints in the vDSO code
 147          * pages though.
 148          */
 149         vma = _install_special_mapping(mm, vdso_base, vdso_pages << PAGE_SHIFT,
 150                                        VM_READ|VM_EXEC|
 151                                        VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
 152                                        &vdso_mapping);
 153         if (IS_ERR(vma)) {
 154                 rc = PTR_ERR(vma);
 155                 goto out_up;
 156         }
 157
 158         current->mm->context.vdso_base = vdso_base;
 159         rc = 0;
 160
 161 out_up:
 162         mmap_write_unlock(mm);
 163         return rc;
 164 }
 165
 166 static int __init vdso_init(void)
 167 {
 168         int i;
 169
 170         vdso_getcpu_init();
 171         /* Calculate the size of the 64 bit vDSO */
 172         vdso64_pages = ((&vdso64_end - &vdso64_start
 173                          + PAGE_SIZE - 1) >> PAGE_SHIFT) + 1;
 174
 175         /* Make sure pages are in the correct state */
 176         vdso64_pagelist = kcalloc(vdso64_pages + 1, sizeof(struct page *),
 177                                   GFP_KERNEL);
 178         BUG_ON(vdso64_pagelist == NULL);
 179         for (i = 0; i < vdso64_pages - 1; i++) {
 180                 struct page *pg = virt_to_page(vdso64_kbase + i*PAGE_SIZE);
 181                 get_page(pg);
 182                 vdso64_pagelist[i] = pg;
 183         }
 184         vdso64_pagelist[vdso64_pages - 1] = virt_to_page(vdso_data);
 185         vdso64_pagelist[vdso64_pages] = NULL;
 186
 187         get_page(virt_to_page(vdso_data));
 188
 189         return 0;
 190 }
 191 early_initcall(vdso_init);