1 files changed, 59 insertions, 45 deletions

diff --git a/arch/um/kernel/skas/mmu.c b/arch/um/kernel/skas/mmu.c
index 6da9ab4f5a18..e8dc8540d444 100644
--- a/arch/um/kernel/skas/mmu.c
+++ b/arch/um/kernel/skas/mmu.c
@@ -34,25 +34,6 @@ static int init_stub_pte(struct mm_struct *mm, unsigned long 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;
@@ -76,24 +57,6 @@ int init_new_context(struct task_struct *task, struct mm_struct *mm)
                 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;
@@ -137,6 +100,64 @@ int init_new_context(struct task_struct *task, struct mm_struct *mm)
         return ret;
 }
 
+void arch_dup_mmap(struct mm_struct *oldmm, struct mm_struct *mm)
+{
+        struct page **pages;
+        int err, ret;
+
+        if (!skas_needs_stub)
+                return;
+
+        ret = init_stub_pte(mm, STUB_CODE,
+                            (unsigned long) &__syscall_stub_start);
+        if (ret)
+                goto out;
+
+        ret = init_stub_pte(mm, STUB_DATA, mm->context.id.stack);
+        if (ret)
+                goto out;
+
+        pages = kmalloc(2 * sizeof(struct page *), GFP_KERNEL);
+        if (pages == NULL) {
+                printk(KERN_ERR "arch_dup_mmap failed to allocate 2 page "
+                       "pointers\n");
+                goto out;
+        }
+
+        pages[0] = virt_to_page(&__syscall_stub_start);
+        pages[1] = virt_to_page(mm->context.id.stack);
+
+        /* dup_mmap already holds mmap_sem */
+        err = install_special_mapping(mm, STUB_START, STUB_END - STUB_START,
+                                      VM_READ | VM_MAYREAD | VM_EXEC |
+                                      VM_MAYEXEC | VM_DONTCOPY, pages);
+        if (err) {
+                printk(KERN_ERR "install_special_mapping returned %d\n", err);
+                goto out_free;
+        }
+        return;
+
+out_free:
+        kfree(pages);
+out:
+        force_sigsegv(SIGSEGV, current);
+}
+
+void arch_exit_mmap(struct mm_struct *mm)
+{
+        pte_t *pte;
+
+        pte = virt_to_pte(mm, STUB_CODE);
+        if (pte != NULL)
+                pte_clear(mm, STUB_CODE, pte);
+
+        pte = virt_to_pte(mm, STUB_DATA);
+        if (pte == NULL)
+                return;
+
+        pte_clear(mm, STUB_DATA, pte);
+}
+
 void destroy_context(struct mm_struct *mm)
 {
         struct mm_context *mmu = &mm->context;
@@ -146,15 +167,8 @@ void destroy_context(struct mm_struct *mm)
         else
                 os_kill_ptraced_process(mmu->id.u.pid, 1);
 
-        if (!proc_mm || !ptrace_faultinfo) {
+        if (skas_needs_stub)
                 free_page(mmu->id.stack);
-                pte_lock_deinit(virt_to_page(mmu->last_page_table));
-                pte_free_kernel(mm, (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(mm, (pmd_t *) mmu->last_pmd);
-#endif
-        }
 
         free_ldt(mmu);
 }