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 "as-layout.h"
  11 #include "os.h"
  12 #include "skas.h"
  13
  14 extern int __syscall_stub_start;
  15
  16 static int init_stub_pte(struct mm_struct *mm, unsigned long proc,
  17                          unsigned long kernel)
  18 {
  19         pgd_t *pgd;
  20         pud_t *pud;
  21         pmd_t *pmd;
  22         pte_t *pte;
  23
  24         pgd = pgd_offset(mm, proc);
  25         pud = pud_alloc(mm, pgd, proc);
  26         if (!pud)
  27                 goto out;
  28
  29         pmd = pmd_alloc(mm, pud, proc);
  30         if (!pmd)
  31                 goto out_pmd;
  32
  33         pte = pte_alloc_map(mm, pmd, proc);
  34         if (!pte)
  35                 goto out_pte;
  36
  37         /*
  38          * There's an interaction between the skas0 stub pages, stack
  39          * randomization, and the BUG at the end of exit_mmap.  exit_mmap
  40          * checks that the number of page tables freed is the same as had
  41          * been allocated.  If the stack is on the last page table page,
  42          * then the stack pte page will be freed, and if not, it won't.  To
  43          * avoid having to know where the stack is, or if the process mapped
  44          * something at the top of its address space for some other reason,
  45          * we set TASK_SIZE to end at the start of the last page table.
  46          * This keeps exit_mmap off the last page, but introduces a leak
  47          * of that page.  So, we hang onto it here and free it in
  48          * destroy_context_skas.
  49          */
  50
  51         mm->context.last_page_table = pmd_page_vaddr(*pmd);
  52 #ifdef CONFIG_3_LEVEL_PGTABLES
  53         mm->context.last_pmd = (unsigned long) __va(pud_val(*pud));
  54 #endif
  55
  56         *pte = mk_pte(virt_to_page(kernel), __pgprot(_PAGE_PRESENT));
  57         *pte = pte_mkread(*pte);
  58         return 0;
  59
  60  out_pmd:
  61         pud_free(pud);
  62  out_pte:
  63         pmd_free(pmd);
  64  out:
  65         return -ENOMEM;
  66 }
  67
  68 int init_new_context(struct task_struct *task, struct mm_struct *mm)
  69 {
  70         struct mm_context *from_mm = NULL;
  71         struct mm_context *to_mm = &mm->context;
  72         unsigned long stack = 0;
  73         int ret = -ENOMEM;
  74
  75         if (skas_needs_stub) {
  76                 stack = get_zeroed_page(GFP_KERNEL);
  77                 if (stack == 0)
  78                         goto out;
  79
  80                 /*
  81                  * This zeros the entry that pgd_alloc didn't, needed since
  82                  * we are about to reinitialize it, and want mm.nr_ptes to
  83                  * be accurate.
  84                  */
  85                 mm->pgd[USER_PTRS_PER_PGD] = __pgd(0);
  86
  87                 ret = init_stub_pte(mm, STUB_CODE,
  88                                     (unsigned long) &__syscall_stub_start);
  89                 if (ret)
  90                         goto out_free;
  91
  92                 ret = init_stub_pte(mm, STUB_DATA, stack);
  93                 if (ret)
  94                         goto out_free;
  95
  96                 mm->nr_ptes--;
  97         }
  98
  99         to_mm->id.stack = stack;
 100         if (current->mm != NULL && current->mm != &init_mm)
 101                 from_mm = &current->mm->context;
 102
 103         if (proc_mm) {
 104                 ret = new_mm(stack);
 105                 if (ret < 0) {
 106                         printk(KERN_ERR "init_new_context_skas - "
 107                                "new_mm failed, errno = %d\n", ret);
 108                         goto out_free;
 109                 }
 110                 to_mm->id.u.mm_fd = ret;
 111         }
 112         else {
 113                 if (from_mm)
 114                         to_mm->id.u.pid = copy_context_skas0(stack,
 115                                                              from_mm->id.u.pid);
 116                 else to_mm->id.u.pid = start_userspace(stack);
 117         }
 118
 119         ret = init_new_ldt(to_mm, from_mm);
 120         if (ret < 0) {
 121                 printk(KERN_ERR "init_new_context_skas - init_ldt"
 122                        " failed, errno = %d\n", ret);
 123                 goto out_free;
 124         }
 125
 126         return 0;
 127
 128  out_free:
 129         if (to_mm->id.stack != 0)
 130                 free_page(to_mm->id.stack);
 131  out:
 132         return ret;
 133 }
 134
 135 void destroy_context(struct mm_struct *mm)
 136 {
 137         struct mm_context *mmu = &mm->context;
 138
 139         if (proc_mm)
 140                 os_close_file(mmu->id.u.mm_fd);
 141         else
 142                 os_kill_ptraced_process(mmu->id.u.pid, 1);
 143
 144         if (!proc_mm || !ptrace_faultinfo) {
 145                 free_page(mmu->id.stack);
 146                 pte_lock_deinit(virt_to_page(mmu->last_page_table));
 147                 pte_free_kernel((pte_t *) mmu->last_page_table);
 148                 dec_zone_page_state(virt_to_page(mmu->last_page_table), NR_PAGETABLE);
 149 #ifdef CONFIG_3_LEVEL_PGTABLES
 150                 pmd_free((pmd_t *) mmu->last_pmd);
 151 #endif
 152         }
 153
 154         free_ldt(mmu);
 155 }