arch/um/kernel/skas/mmu.c

   1 /*
   2  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
   3  * Licensed under the GPL
   4  */
   5
   6 #include "linux/mm.h"
   7 #include "linux/sched.h"
   8 #include "asm/pgalloc.h"
   9 #include "asm/pgtable.h"
  10 #include "os.h"
  11 #include "skas.h"
  12
  13 extern int __syscall_stub_start;
  14
  15 static int init_stub_pte(struct mm_struct *mm, unsigned long proc,
  16                          unsigned long kernel)
  17 {
  18         pgd_t *pgd;
  19         pud_t *pud;
  20         pmd_t *pmd;
  21         pte_t *pte;
  22
  23         pgd = pgd_offset(mm, proc);
  24         pud = pud_alloc(mm, pgd, proc);
  25         if (!pud)
  26                 goto out;
  27
  28         pmd = pmd_alloc(mm, pud, proc);
  29         if (!pmd)
  30                 goto out_pmd;
  31
  32         pte = pte_alloc_map(mm, pmd, proc);
  33         if (!pte)
  34                 goto out_pte;
  35
  36         /*
  37          * There's an interaction between the skas0 stub pages, stack
  38          * randomization, and the BUG at the end of exit_mmap.  exit_mmap
  39          * checks that the number of page tables freed is the same as had
  40          * been allocated.  If the stack is on the last page table page,
  41          * then the stack pte page will be freed, and if not, it won't.  To
  42          * avoid having to know where the stack is, or if the process mapped
  43          * something at the top of its address space for some other reason,
  44          * we set TASK_SIZE to end at the start of the last page table.
  45          * This keeps exit_mmap off the last page, but introduces a leak
  46          * of that page.  So, we hang onto it here and free it in
  47          * destroy_context_skas.
  48          */
  49
  50         mm->context.last_page_table = pmd_page_vaddr(*pmd);
  51 #ifdef CONFIG_3_LEVEL_PGTABLES
  52         mm->context.last_pmd = (unsigned long) __va(pud_val(*pud));
  53 #endif
  54
  55         *pte = mk_pte(virt_to_page(kernel), __pgprot(_PAGE_PRESENT));
  56         *pte = pte_mkread(*pte);
  57         return 0;
  58
  59  out_pmd:
  60         pud_free(pud);
  61  out_pte:
  62         pmd_free(pmd);
  63  out:
  64         return -ENOMEM;
  65 }
  66
  67 int init_new_context(struct task_struct *task, struct mm_struct *mm)
  68 {
  69         struct mm_context *from_mm = NULL;
  70         struct mm_context *to_mm = &mm->context;
  71         unsigned long stack = 0;
  72         int ret = -ENOMEM;
  73
  74         if (skas_needs_stub) {
  75                 stack = get_zeroed_page(GFP_KERNEL);
  76                 if (stack == 0)
  77                         goto out;
  78
  79                 /*
  80                  * This zeros the entry that pgd_alloc didn't, needed since
  81                  * we are about to reinitialize it, and want mm.nr_ptes to
  82                  * be accurate.
  83                  */
  84                 mm->pgd[USER_PTRS_PER_PGD] = __pgd(0);
  85
  86                 ret = init_stub_pte(mm, CONFIG_STUB_CODE,
  87                                     (unsigned long) &__syscall_stub_start);
  88                 if (ret)
  89                         goto out_free;
  90
  91                 ret = init_stub_pte(mm, CONFIG_STUB_DATA, stack);
  92                 if (ret)
  93                         goto out_free;
  94
  95                 mm->nr_ptes--;
  96         }
  97
  98         to_mm->id.stack = stack;
  99         if (current->mm != NULL && current->mm != &init_mm)
 100                 from_mm = &current->mm->context;
 101
 102         if (proc_mm) {
 103                 ret = new_mm(stack);
 104                 if (ret < 0) {
 105                         printk(KERN_ERR "init_new_context_skas - "
 106                                "new_mm failed, errno = %d\n", ret);
 107                         goto out_free;
 108                 }
 109                 to_mm->id.u.mm_fd = ret;
 110         }
 111         else {
 112                 if (from_mm)
 113                         to_mm->id.u.pid = copy_context_skas0(stack,
 114                                                              from_mm->id.u.pid);
 115                 else to_mm->id.u.pid = start_userspace(stack);
 116         }
 117
 118         ret = init_new_ldt(to_mm, from_mm);
 119         if (ret < 0) {
 120                 printk(KERN_ERR "init_new_context_skas - init_ldt"
 121                        " failed, errno = %d\n", ret);
 122                 goto out_free;
 123         }
 124
 125         return 0;
 126
 127  out_free:
 128         if (to_mm->id.stack != 0)
 129                 free_page(to_mm->id.stack);
 130  out:
 131         return ret;
 132 }
 133
 134 void destroy_context(struct mm_struct *mm)
 135 {
 136         struct mm_context *mmu = &mm->context;
 137
 138         if (proc_mm)
 139                 os_close_file(mmu->id.u.mm_fd);
 140         else
 141                 os_kill_ptraced_process(mmu->id.u.pid, 1);
 142
 143         if (!proc_mm || !ptrace_faultinfo) {
 144                 free_page(mmu->id.stack);
 145                 pte_lock_deinit(virt_to_page(mmu->last_page_table));
 146                 pte_free_kernel((pte_t *) mmu->last_page_table);
 147                 dec_zone_page_state(virt_to_page(mmu->last_page_table), NR_PAGETABLE);
 148 #ifdef CONFIG_3_LEVEL_PGTABLES
 149                 pmd_free((pmd_t *) mmu->last_pmd);
 150 #endif
 151         }
 152
 153         free_ldt(mmu);
 154 }