arch/um/kernel/skas/mmu.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
   4  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
   5  */
   6
   7 #include <linux/mm.h>
   8 #include <linux/sched/signal.h>
   9 #include <linux/slab.h>
  10
  11 #include <asm/pgalloc.h>
  12 #include <asm/pgtable.h>
  13 #include <asm/sections.h>
  14 #include <as-layout.h>
  15 #include <os.h>
  16 #include <skas.h>
  17
  18 static int init_stub_pte(struct mm_struct *mm, unsigned long proc,
  19                          unsigned long kernel)
  20 {
  21         pgd_t *pgd;
  22         p4d_t *p4d;
  23         pud_t *pud;
  24         pmd_t *pmd;
  25         pte_t *pte;
  26
  27         pgd = pgd_offset(mm, proc);
  28
  29         p4d = p4d_alloc(mm, pgd, proc);
  30         if (!p4d)
  31                 goto out;
  32
  33         pud = pud_alloc(mm, p4d, proc);
  34         if (!pud)
  35                 goto out_pud;
  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         *pte = mk_pte(virt_to_page(kernel), __pgprot(_PAGE_PRESENT));
  46         *pte = pte_mkread(*pte);
  47         return 0;
  48
  49  out_pte:
  50         pmd_free(mm, pmd);
  51  out_pmd:
  52         pud_free(mm, pud);
  53  out_pud:
  54         p4d_free(mm, p4d);
  55  out:
  56         return -ENOMEM;
  57 }
  58
  59 int init_new_context(struct task_struct *task, struct mm_struct *mm)
  60 {
  61         struct mm_context *from_mm = NULL;
  62         struct mm_context *to_mm = &mm->context;
  63         unsigned long stack = 0;
  64         int ret = -ENOMEM;
  65
  66         stack = get_zeroed_page(GFP_KERNEL);
  67         if (stack == 0)
  68                 goto out;
  69
  70         to_mm->id.stack = stack;
  71         if (current->mm != NULL && current->mm != &init_mm)
  72                 from_mm = &current->mm->context;
  73
  74         block_signals_trace();
  75         if (from_mm)
  76                 to_mm->id.u.pid = copy_context_skas0(stack,
  77                                                      from_mm->id.u.pid);
  78         else to_mm->id.u.pid = start_userspace(stack);
  79         unblock_signals_trace();
  80
  81         if (to_mm->id.u.pid < 0) {
  82                 ret = to_mm->id.u.pid;
  83                 goto out_free;
  84         }
  85
  86         ret = init_new_ldt(to_mm, from_mm);
  87         if (ret < 0) {
  88                 printk(KERN_ERR "init_new_context_skas - init_ldt"
  89                        " failed, errno = %d\n", ret);
  90                 goto out_free;
  91         }
  92
  93         return 0;
  94
  95  out_free:
  96         if (to_mm->id.stack != 0)
  97                 free_page(to_mm->id.stack);
  98  out:
  99         return ret;
 100 }
 101
 102 void uml_setup_stubs(struct mm_struct *mm)
 103 {
 104         int err, ret;
 105
 106         ret = init_stub_pte(mm, STUB_CODE,
 107                             (unsigned long) __syscall_stub_start);
 108         if (ret)
 109                 goto out;
 110
 111         ret = init_stub_pte(mm, STUB_DATA, mm->context.id.stack);
 112         if (ret)
 113                 goto out;
 114
 115         mm->context.stub_pages[0] = virt_to_page(__syscall_stub_start);
 116         mm->context.stub_pages[1] = virt_to_page(mm->context.id.stack);
 117
 118         /* dup_mmap already holds mmap_sem */
 119         err = install_special_mapping(mm, STUB_START, STUB_END - STUB_START,
 120                                       VM_READ | VM_MAYREAD | VM_EXEC |
 121                                       VM_MAYEXEC | VM_DONTCOPY | VM_PFNMAP,
 122                                       mm->context.stub_pages);
 123         if (err) {
 124                 printk(KERN_ERR "install_special_mapping returned %d\n", err);
 125                 goto out;
 126         }
 127         return;
 128
 129 out:
 130         force_sigsegv(SIGSEGV);
 131 }
 132
 133 void arch_exit_mmap(struct mm_struct *mm)
 134 {
 135         pte_t *pte;
 136
 137         pte = virt_to_pte(mm, STUB_CODE);
 138         if (pte != NULL)
 139                 pte_clear(mm, STUB_CODE, pte);
 140
 141         pte = virt_to_pte(mm, STUB_DATA);
 142         if (pte == NULL)
 143                 return;
 144
 145         pte_clear(mm, STUB_DATA, pte);
 146 }
 147
 148 void destroy_context(struct mm_struct *mm)
 149 {
 150         struct mm_context *mmu = &mm->context;
 151
 152         /*
 153          * If init_new_context wasn't called, this will be
 154          * zero, resulting in a kill(0), which will result in the
 155          * whole UML suddenly dying.  Also, cover negative and
 156          * 1 cases, since they shouldn't happen either.
 157          */
 158         if (mmu->id.u.pid < 2) {
 159                 printk(KERN_ERR "corrupt mm_context - pid = %d\n",
 160                        mmu->id.u.pid);
 161                 return;
 162         }
 163         os_kill_ptraced_process(mmu->id.u.pid, 1);
 164
 165         free_page(mmu->id.stack);
 166         free_ldt(mmu);
 167 }