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