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/sched.h"
   7 #include "linux/list.h"
   8 #include "linux/spinlock.h"
   9 #include "linux/slab.h"
  10 #include "linux/errno.h"
  11 #include "linux/mm.h"
  12 #include "asm/current.h"
  13 #include "asm/segment.h"
  14 #include "asm/mmu.h"
  15 #include "asm/pgalloc.h"
  16 #include "asm/pgtable.h"
  17 #include "asm/ldt.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         pgd = pgd_offset(mm, proc);
  32         pud = pud_alloc(mm, pgd, proc);
  33         if (!pud)
  34                 goto out;
  35
  36         pmd = pmd_alloc(mm, pud, proc);
  37         if (!pmd)
  38                 goto out_pmd;
  39
  40         pte = pte_alloc_map(mm, pmd, proc);
  41         if (!pte)
  42                 goto out_pte;
  43
  44         /* There's an interaction between the skas0 stub pages, stack
  45          * randomization, and the BUG at the end of exit_mmap.  exit_mmap
  46          * checks that the number of page tables freed is the same as had
  47          * been allocated.  If the stack is on the last page table page,
  48          * then the stack pte page will be freed, and if not, it won't.  To
  49          * avoid having to know where the stack is, or if the process mapped
  50          * something at the top of its address space for some other reason,
  51          * we set TASK_SIZE to end at the start of the last page table.
  52          * This keeps exit_mmap off the last page, but introduces a leak
  53          * of that page.  So, we hang onto it here and free it in
  54          * destroy_context_skas.
  55          */
  56
  57         mm->context.skas.last_page_table = pmd_page_vaddr(*pmd);
  58 #ifdef CONFIG_3_LEVEL_PGTABLES
  59         mm->context.skas.last_pmd = (unsigned long) __va(pud_val(*pud));
  60 #endif
  61
  62         *pte = mk_pte(virt_to_page(kernel), __pgprot(_PAGE_PRESENT));
  63         /* This is wrong for the code page, but it doesn't matter since the
  64          * stub is mapped by hand with the correct permissions.
  65          */
  66         *pte = pte_mkwrite(*pte);
  67         return(0);
  68
  69  out_pmd:
  70         pud_free(pud);
  71  out_pte:
  72         pmd_free(pmd);
  73  out:
  74         return(-ENOMEM);
  75 }
  76
  77 int init_new_context_skas(struct task_struct *task, struct mm_struct *mm)
  78 {
  79         struct mmu_context_skas *from_mm = NULL;
  80         struct mmu_context_skas *to_mm = &mm->context.skas;
  81         unsigned long stack = 0;
  82         int ret = -ENOMEM;
  83
  84         if(skas_needs_stub){
  85                 stack = get_zeroed_page(GFP_KERNEL);
  86                 if(stack == 0)
  87                         goto out;
  88
  89                 /* This zeros the entry that pgd_alloc didn't, needed since
  90                  * we are about to reinitialize it, and want mm.nr_ptes to
  91                  * be accurate.
  92                  */
  93                 mm->pgd[USER_PTRS_PER_PGD] = __pgd(0);
  94
  95                 ret = init_stub_pte(mm, CONFIG_STUB_CODE,
  96                                     (unsigned long) &__syscall_stub_start);
  97                 if(ret)
  98                         goto out_free;
  99
 100                 ret = init_stub_pte(mm, CONFIG_STUB_DATA, stack);
 101                 if(ret)
 102                         goto out_free;
 103
 104                 mm->nr_ptes--;
 105         }
 106
 107         to_mm->id.stack = stack;
 108         if(current->mm != NULL && current->mm != &init_mm)
 109                 from_mm = &current->mm->context.skas;
 110
 111         if(proc_mm){
 112                 ret = new_mm(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                 to_mm->id.u.mm_fd = ret;
 119         }
 120         else {
 121                 if(from_mm)
 122                         to_mm->id.u.pid = copy_context_skas0(stack,
 123                                                              from_mm->id.u.pid);
 124                 else to_mm->id.u.pid = start_userspace(stack);
 125         }
 126
 127         ret = init_new_ldt(to_mm, from_mm);
 128         if(ret < 0){
 129                 printk("init_new_context_skas - init_ldt"
 130                        " failed, errno = %d\n", ret);
 131                 goto out_free;
 132         }
 133
 134         return 0;
 135
 136  out_free:
 137         if(to_mm->id.stack != 0)
 138                 free_page(to_mm->id.stack);
 139  out:
 140         return ret;
 141 }
 142
 143 void destroy_context_skas(struct mm_struct *mm)
 144 {
 145         struct mmu_context_skas *mmu = &mm->context.skas;
 146
 147         if(proc_mm)
 148                 os_close_file(mmu->id.u.mm_fd);
 149         else
 150                 os_kill_ptraced_process(mmu->id.u.pid, 1);
 151
 152         if(!proc_mm || !ptrace_faultinfo){
 153                 free_page(mmu->id.stack);
 154                 pte_lock_deinit(virt_to_page(mmu->last_page_table));
 155                 pte_free_kernel((pte_t *) mmu->last_page_table);
 156                 dec_zone_page_state(virt_to_page(mmu->last_page_table), NR_PAGETABLE);
 157 #ifdef CONFIG_3_LEVEL_PGTABLES
 158                 pmd_free((pmd_t *) mmu->last_pmd);
 159 #endif
 160         }
 161 }