arch/um/kernel/skas/mmu.c

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