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 "asm/ldt.h"
  19 #include "os.h"
  20 #include "skas.h"
  21
  22 extern int __syscall_stub_start;
  23
  24 static int init_stub_pte(struct mm_struct *mm, unsigned long proc,
  25                          unsigned long kernel)
  26 {
  27         pgd_t *pgd;
  28         pud_t *pud;
  29         pmd_t *pmd;
  30         pte_t *pte;
  31
  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_vaddr(*pmd);
  59 #ifdef CONFIG_3_LEVEL_PGTABLES
  60         mm->context.skas.last_pmd = (unsigned long) __va(pud_val(*pud));
  61 #endif
  62
  63         *pte = mk_pte(virt_to_page(kernel), __pgprot(_PAGE_PRESENT));
  64         /* This is wrong for the code page, but it doesn't matter since the
  65          * stub is mapped by hand with the correct permissions.
  66          */
  67         *pte = pte_mkwrite(*pte);
  68         return(0);
  69
  70  out_pmd:
  71         pud_free(pud);
  72  out_pte:
  73         pmd_free(pmd);
  74  out:
  75         return(-ENOMEM);
  76 }
  77
  78 int init_new_context_skas(struct task_struct *task, struct mm_struct *mm)
  79 {
  80         struct mmu_context_skas *from_mm = NULL;
  81         struct mmu_context_skas *to_mm = &mm->context.skas;
  82         unsigned long stack = 0;
  83         int ret = -ENOMEM;
  84
  85         if(skas_needs_stub){
  86                 stack = get_zeroed_page(GFP_KERNEL);
  87                 if(stack == 0)
  88                         goto out;
  89
  90                 /* This zeros the entry that pgd_alloc didn't, needed since
  91                  * we are about to reinitialize it, and want mm.nr_ptes to
  92                  * be accurate.
  93                  */
  94                 mm->pgd[USER_PTRS_PER_PGD] = __pgd(0);
  95
  96                 ret = init_stub_pte(mm, CONFIG_STUB_CODE,
  97                                     (unsigned long) &__syscall_stub_start);
  98                 if(ret)
  99                         goto out_free;
 100
 101                 ret = init_stub_pte(mm, CONFIG_STUB_DATA, stack);
 102                 if(ret)
 103                         goto out_free;
 104
 105                 mm->nr_ptes--;
 106         }
 107
 108         to_mm->id.stack = stack;
 109         if(current->mm != NULL && current->mm != &init_mm)
 110                 from_mm = &current->mm->context.skas;
 111
 112         if(proc_mm){
 113                 ret = new_mm(stack);
 114                 if(ret < 0){
 115                         printk("init_new_context_skas - new_mm failed, "
 116                                "errno = %d\n", ret);
 117                         goto out_free;
 118                 }
 119                 to_mm->id.u.mm_fd = ret;
 120         }
 121         else {
 122                 if(from_mm)
 123                         to_mm->id.u.pid = copy_context_skas0(stack,
 124                                                              from_mm->id.u.pid);
 125                 else to_mm->id.u.pid = start_userspace(stack);
 126         }
 127
 128         ret = init_new_ldt(to_mm, from_mm);
 129         if(ret < 0){
 130                 printk("init_new_context_skas - init_ldt"
 131                        " failed, errno = %d\n", ret);
 132                 goto out_free;
 133         }
 134
 135         return 0;
 136
 137  out_free:
 138         if(to_mm->id.stack != 0)
 139                 free_page(to_mm->id.stack);
 140  out:
 141         return ret;
 142 }
 143
 144 void destroy_context_skas(struct mm_struct *mm)
 145 {
 146         struct mmu_context_skas *mmu = &mm->context.skas;
 147
 148         if(proc_mm)
 149                 os_close_file(mmu->id.u.mm_fd);
 150         else
 151                 os_kill_ptraced_process(mmu->id.u.pid, 1);
 152
 153         if(!proc_mm || !ptrace_faultinfo){
 154                 free_page(mmu->id.stack);
 155                 pte_lock_deinit(virt_to_page(mmu->last_page_table));
 156                 pte_free_kernel((pte_t *) mmu->last_page_table);
 157                 dec_zone_page_state(virt_to_page(mmu->last_page_table), NR_PAGETABLE);
 158 #ifdef CONFIG_3_LEVEL_PGTABLES
 159                 pmd_free((pmd_t *) mmu->last_pmd);
 160 #endif
 161         }
 162 }