+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.skas.last_page_table = pmd_page_kernel(*pmd);
+#ifdef CONFIG_3_LEVEL_PGTABLES
+ mm->context.skas.last_pmd = (unsigned long) __va(pud_val(*pud));
+#endif
+
+ *pte = mk_pte(virt_to_page(kernel), __pgprot(_PAGE_PRESENT));
+ *pte = pte_mkexec(*pte);
+ *pte = pte_wrprotect(*pte);
+ return(0);
+
+ out_pmd:
+ pud_free(pud);
+ out_pte:
+ pmd_free(pmd);
+ out:
+ return(-ENOMEM);
+}
+