arch/tile/kernel/vdso.c

   1 /*
   2  * Copyright 2012 Tilera Corporation. All Rights Reserved.
   3  *
   4  *   This program is free software; you can redistribute it and/or
   5  *   modify it under the terms of the GNU General Public License
   6  *   as published by the Free Software Foundation, version 2.
   7  *
   8  *   This program is distributed in the hope that it will be useful, but
   9  *   WITHOUT ANY WARRANTY; without even the implied warranty of
  10  *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
  11  *   NON INFRINGEMENT.  See the GNU General Public License for
  12  *   more details.
  13  */
  14
  15 #include <linux/binfmts.h>
  16 #include <linux/compat.h>
  17 #include <linux/elf.h>
  18 #include <linux/mm.h>
  19 #include <linux/pagemap.h>
  20
  21 #include <asm/vdso.h>
  22 #include <asm/mman.h>
  23 #include <asm/sections.h>
  24
  25 #include <arch/sim.h>
  26
  27 /* The alignment of the vDSO. */
  28 #define VDSO_ALIGNMENT  PAGE_SIZE
  29
  30
  31 static unsigned int vdso_pages;
  32 static struct page **vdso_pagelist;
  33
  34 #ifdef CONFIG_COMPAT
  35 static unsigned int vdso32_pages;
  36 static struct page **vdso32_pagelist;
  37 #endif
  38 static int vdso_ready;
  39
  40 /*
  41  * The vdso data page.
  42  */
  43 static union {
  44         struct vdso_data        data;
  45         u8                      page[PAGE_SIZE];
  46 } vdso_data_store __page_aligned_data;
  47
  48 struct vdso_data *vdso_data = &vdso_data_store.data;
  49
  50 static unsigned int __read_mostly vdso_enabled = 1;
  51
  52 static struct page **vdso_setup(void *vdso_kbase, unsigned int pages)
  53 {
  54         int i;
  55         struct page **pagelist;
  56
  57         pagelist = kzalloc(sizeof(struct page *) * (pages + 1), GFP_KERNEL);
  58         BUG_ON(pagelist == NULL);
  59         for (i = 0; i < pages - 1; i++) {
  60                 struct page *pg = virt_to_page(vdso_kbase + i*PAGE_SIZE);
  61                 ClearPageReserved(pg);
  62                 pagelist[i] = pg;
  63         }
  64         pagelist[pages - 1] = virt_to_page(vdso_data);
  65         pagelist[pages] = NULL;
  66
  67         return pagelist;
  68 }
  69
  70 static int __init vdso_init(void)
  71 {
  72         int data_pages = sizeof(vdso_data_store) >> PAGE_SHIFT;
  73
  74         /*
  75          * We can disable vDSO support generally, but we need to retain
  76          * one page to support the two-bundle (16-byte) rt_sigreturn path.
  77          */
  78         if (!vdso_enabled) {
  79                 size_t offset = (unsigned long)&__vdso_rt_sigreturn;
  80                 static struct page *sigret_page;
  81                 sigret_page = alloc_page(GFP_KERNEL | __GFP_ZERO);
  82                 BUG_ON(sigret_page == NULL);
  83                 vdso_pagelist = &sigret_page;
  84                 vdso_pages = 1;
  85                 BUG_ON(offset >= PAGE_SIZE);
  86                 memcpy(page_address(sigret_page) + offset,
  87                        vdso_start + offset, 16);
  88 #ifdef CONFIG_COMPAT
  89                 vdso32_pages = vdso_pages;
  90                 vdso32_pagelist = vdso_pagelist;
  91 #endif
  92                 vdso_ready = 1;
  93                 return 0;
  94         }
  95
  96         vdso_pages = (vdso_end - vdso_start) >> PAGE_SHIFT;
  97         vdso_pages += data_pages;
  98         vdso_pagelist = vdso_setup(vdso_start, vdso_pages);
  99
 100 #ifdef CONFIG_COMPAT
 101         vdso32_pages = (vdso32_end - vdso32_start) >> PAGE_SHIFT;
 102         vdso32_pages += data_pages;
 103         vdso32_pagelist = vdso_setup(vdso32_start, vdso32_pages);
 104 #endif
 105
 106         smp_wmb();
 107         vdso_ready = 1;
 108
 109         return 0;
 110 }
 111 arch_initcall(vdso_init);
 112
 113 const char *arch_vma_name(struct vm_area_struct *vma)
 114 {
 115         if (vma->vm_mm && vma->vm_start == VDSO_BASE)
 116                 return "[vdso]";
 117 #ifndef __tilegx__
 118         if (vma->vm_start == MEM_USER_INTRPT)
 119                 return "[intrpt]";
 120 #endif
 121         return NULL;
 122 }
 123
 124 int setup_vdso_pages(void)
 125 {
 126         struct page **pagelist;
 127         unsigned long pages;
 128         struct mm_struct *mm = current->mm;
 129         unsigned long vdso_base = 0;
 130         int retval = 0;
 131
 132         if (!vdso_ready)
 133                 return 0;
 134
 135         mm->context.vdso_base = 0;
 136
 137         pagelist = vdso_pagelist;
 138         pages = vdso_pages;
 139 #ifdef CONFIG_COMPAT
 140         if (is_compat_task()) {
 141                 pagelist = vdso32_pagelist;
 142                 pages = vdso32_pages;
 143         }
 144 #endif
 145
 146         /*
 147          * vDSO has a problem and was disabled, just don't "enable" it for the
 148          * process.
 149          */
 150         if (pages == 0)
 151                 return 0;
 152
 153         vdso_base = get_unmapped_area(NULL, vdso_base,
 154                                       (pages << PAGE_SHIFT) +
 155                                       ((VDSO_ALIGNMENT - 1) & PAGE_MASK),
 156                                       0, 0);
 157         if (IS_ERR_VALUE(vdso_base)) {
 158                 retval = vdso_base;
 159                 return retval;
 160         }
 161
 162         /* Add required alignment. */
 163         vdso_base = ALIGN(vdso_base, VDSO_ALIGNMENT);
 164
 165         /*
 166          * Put vDSO base into mm struct. We need to do this before calling
 167          * install_special_mapping or the perf counter mmap tracking code
 168          * will fail to recognise it as a vDSO (since arch_vma_name fails).
 169          */
 170         mm->context.vdso_base = vdso_base;
 171
 172         /*
 173          * our vma flags don't have VM_WRITE so by default, the process isn't
 174          * allowed to write those pages.
 175          * gdb can break that with ptrace interface, and thus trigger COW on
 176          * those pages but it's then your responsibility to never do that on
 177          * the "data" page of the vDSO or you'll stop getting kernel updates
 178          * and your nice userland gettimeofday will be totally dead.
 179          * It's fine to use that for setting breakpoints in the vDSO code
 180          * pages though
 181          */
 182         retval = install_special_mapping(mm, vdso_base,
 183                                          pages << PAGE_SHIFT,
 184                                          VM_READ|VM_EXEC |
 185                                          VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC,
 186                                          pagelist);
 187         if (retval)
 188                 mm->context.vdso_base = 0;
 189
 190         return retval;
 191 }
 192
 193 static __init int vdso_func(char *s)
 194 {
 195         return kstrtouint(s, 0, &vdso_enabled);
 196 }
 197 __setup("vdso=", vdso_func);