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mmu.c

/*
 * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 * Licensed under the GPL
 */

#include "linux/mm.h"
#include "linux/sched.h"
#include "asm/pgalloc.h"
#include "asm/pgtable.h"
#include "as-layout.h"
#include "os.h"
#include "skas.h"

extern int __syscall_stub_start;

static int init_stub_pte(struct mm_struct *mm, unsigned long proc,
                   unsigned long kernel)
{
      pgd_t *pgd;
      pud_t *pud;
      pmd_t *pmd;
      pte_t *pte;

      pgd = pgd_offset(mm, proc);
      pud = pud_alloc(mm, pgd, proc);
      if (!pud)
            goto out;

      pmd = pmd_alloc(mm, pud, proc);
      if (!pmd)
            goto out_pmd;

      pte = pte_alloc_map(mm, pmd, proc);
      if (!pte)
            goto out_pte;

      /*
       * There's an interaction between the skas0 stub pages, stack
       * randomization, and the BUG at the end of exit_mmap.  exit_mmap
       * checks that the number of page tables freed is the same as had
       * been allocated.  If the stack is on the last page table page,
       * then the stack pte page will be freed, and if not, it won't.  To
       * avoid having to know where the stack is, or if the process mapped
       * something at the top of its address space for some other reason,
       * we set TASK_SIZE to end at the start of the last page table.
       * This keeps exit_mmap off the last page, but introduces a leak
       * of that page.  So, we hang onto it here and free it in
       * destroy_context_skas.
       */

      mm->context.last_page_table = pmd_page_vaddr(*pmd);
#ifdef CONFIG_3_LEVEL_PGTABLES
      mm->context.last_pmd = (unsigned long) __va(pud_val(*pud));
#endif

      *pte = mk_pte(virt_to_page(kernel), __pgprot(_PAGE_PRESENT));
      *pte = pte_mkread(*pte);
      return 0;

 out_pmd:
      pud_free(pud);
 out_pte:
      pmd_free(pmd);
 out:
      return -ENOMEM;
}

int init_new_context(struct task_struct *task, struct mm_struct *mm)
{
      struct mm_context *from_mm = NULL;
      struct mm_context *to_mm = &mm->context;
      unsigned long stack = 0;
      int ret = -ENOMEM;

      if (skas_needs_stub) {
            stack = get_zeroed_page(GFP_KERNEL);
            if (stack == 0)
                  goto out;

            /*
             * This zeros the entry that pgd_alloc didn't, needed since
             * we are about to reinitialize it, and want mm.nr_ptes to
             * be accurate.
             */
            mm->pgd[USER_PTRS_PER_PGD] = __pgd(0);

            ret = init_stub_pte(mm, STUB_CODE,
                            (unsigned long) &__syscall_stub_start);
            if (ret)
                  goto out_free;

            ret = init_stub_pte(mm, STUB_DATA, stack);
            if (ret)
                  goto out_free;

            mm->nr_ptes--;
      }

      to_mm->id.stack = stack;
      if (current->mm != NULL && current->mm != &init_mm)
            from_mm = &current->mm->context;

      if (proc_mm) {
            ret = new_mm(stack);
            if (ret < 0) {
                  printk(KERN_ERR "init_new_context_skas - "
                         "new_mm failed, errno = %d\n", ret);
                  goto out_free;
            }
            to_mm->id.u.mm_fd = ret;
      }
      else {
            if (from_mm)
                  to_mm->id.u.pid = copy_context_skas0(stack,
                                               from_mm->id.u.pid);
            else to_mm->id.u.pid = start_userspace(stack);
      }

      ret = init_new_ldt(to_mm, from_mm);
      if (ret < 0) {
            printk(KERN_ERR "init_new_context_skas - init_ldt"
                   " failed, errno = %d\n", ret);
            goto out_free;
      }

      return 0;

 out_free:
      if (to_mm->id.stack != 0)
            free_page(to_mm->id.stack);
 out:
      return ret;
}

void destroy_context(struct mm_struct *mm)
{
      struct mm_context *mmu = &mm->context;

      if (proc_mm)
            os_close_file(mmu->id.u.mm_fd);
      else
            os_kill_ptraced_process(mmu->id.u.pid, 1);

      if (!proc_mm || !ptrace_faultinfo) {
            free_page(mmu->id.stack);
            pte_lock_deinit(virt_to_page(mmu->last_page_table));
            pte_free_kernel((pte_t *) mmu->last_page_table);
            dec_zone_page_state(virt_to_page(mmu->last_page_table), NR_PAGETABLE);
#ifdef CONFIG_3_LEVEL_PGTABLES
            pmd_free((pmd_t *) mmu->last_pmd);
#endif
      }

      free_ldt(mmu);
}

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