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[CS_BASES];
  91         u8                      page[PAGE_SIZE];
  92 } vdso_data_store __page_aligned_data;
  93 struct vdso_data *vdso_data = vdso_data_store.data;
  94
  95 int vdso_getcpu_init(void)
  96 {
  97         set_tod_programmable_field(smp_processor_id());
  98         return 0;
  99 }
 100 early_initcall(vdso_getcpu_init); /* Must be called before SMP init */
 101
 102 /*
 103  * This is called from binfmt_elf, we create the special vma for the
 104  * vDSO and insert it into the mm struct tree
 105  */
 106 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 107 {
 108         struct mm_struct *mm = current->mm;
 109         struct vm_area_struct *vma;
 110         unsigned long vdso_pages;
 111         unsigned long vdso_base;
 112         int rc;
 113
 114         if (!vdso_enabled)
 115                 return 0;
 116
 117         if (is_compat_task())
 118                 return 0;
 119
 120         vdso_pages = vdso64_pages;
 121         /*
 122          * pick a base address for the vDSO in process space. We try to put
 123          * it at vdso_base which is the "natural" base for it, but we might
 124          * fail and end up putting it elsewhere.
 125          */
 126         if (mmap_write_lock_killable(mm))
 127                 return -EINTR;
 128         vdso_base = get_unmapped_area(NULL, 0, vdso_pages << PAGE_SHIFT, 0, 0);
 129         if (IS_ERR_VALUE(vdso_base)) {
 130                 rc = vdso_base;
 131                 goto out_up;
 132         }
 133
 134         /*
 135          * our vma flags don't have VM_WRITE so by default, the process
 136          * isn't allowed to write those pages.
 137          * gdb can break that with ptrace interface, and thus trigger COW
 138          * on those pages but it's then your responsibility to never do that
 139          * on the "data" page of the vDSO or you'll stop getting kernel
 140          * updates and your nice userland gettimeofday will be totally dead.
 141          * It's fine to use that for setting breakpoints in the vDSO code
 142          * pages though.
 143          */
 144         vma = _install_special_mapping(mm, vdso_base, vdso_pages << PAGE_SHIFT,
 145                                        VM_READ|VM_EXEC|
 146                                        VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
 147                                        &vdso_mapping);
 148         if (IS_ERR(vma)) {
 149                 rc = PTR_ERR(vma);
 150                 goto out_up;
 151         }
 152
 153         current->mm->context.vdso_base = vdso_base;
 154         rc = 0;
 155
 156 out_up:
 157         mmap_write_unlock(mm);
 158         return rc;
 159 }
 160
 161 static int __init vdso_init(void)
 162 {
 163         int i;
 164
 165         /* Calculate the size of the 64 bit vDSO */
 166         vdso64_pages = ((&vdso64_end - &vdso64_start) >> PAGE_SHIFT) + 1;
 167
 168         /* Make sure pages are in the correct state */
 169         vdso64_pagelist = kcalloc(vdso64_pages + 1, sizeof(struct page *),
 170                                   GFP_KERNEL);
 171         if (!vdso64_pagelist) {
 172                 vdso_enabled = 0;
 173                 return -ENOMEM;
 174         }
 175         for (i = 0; i < vdso64_pages - 1; i++) {
 176                 struct page *pg = virt_to_page(vdso64_kbase + i*PAGE_SIZE);
 177                 get_page(pg);
 178                 vdso64_pagelist[i] = pg;
 179         }
 180         vdso64_pagelist[vdso64_pages - 1] = virt_to_page(vdso_data);
 181         vdso64_pagelist[vdso64_pages] = NULL;
 182
 183         get_page(virt_to_page(vdso_data));
 184
 185         return 0;
 186 }
 187 arch_initcall(vdso_init);