root/arch/um/kernel/skas/mmu.c

DEFINITIONS

1. init_stub_pte
2. init_new_context
3. uml_setup_stubs
4. arch_exit_mmap
5. destroy_context

   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         pud_t *pud;
  23         pmd_t *pmd;
  24         pte_t *pte;
  25 
  26         pgd = pgd_offset(mm, proc);
  27         pud = pud_alloc(mm, pgd, proc);
  28         if (!pud)
  29                 goto out;
  30 
  31         pmd = pmd_alloc(mm, pud, proc);
  32         if (!pmd)
  33                 goto out_pmd;
  34 
  35         pte = pte_alloc_map(mm, pmd, proc);
  36         if (!pte)
  37                 goto out_pte;
  38 
  39         *pte = mk_pte(virt_to_page(kernel), __pgprot(_PAGE_PRESENT));
  40         *pte = pte_mkread(*pte);
  41         return 0;
  42 
  43  out_pte:
  44         pmd_free(mm, pmd);
  45  out_pmd:
  46         pud_free(mm, pud);
  47  out:
  48         return -ENOMEM;
  49 }
  50 
  51 int init_new_context(struct task_struct *task, struct mm_struct *mm)
  52 {
  53         struct mm_context *from_mm = NULL;
  54         struct mm_context *to_mm = &mm->context;
  55         unsigned long stack = 0;
  56         int ret = -ENOMEM;
  57 
  58         stack = get_zeroed_page(GFP_KERNEL);
  59         if (stack == 0)
  60                 goto out;
  61 
  62         to_mm->id.stack = stack;
  63         if (current->mm != NULL && current->mm != &init_mm)
  64                 from_mm = &current->mm->context;
  65 
  66         block_signals_trace();
  67         if (from_mm)
  68                 to_mm->id.u.pid = copy_context_skas0(stack,
  69                                                      from_mm->id.u.pid);
  70         else to_mm->id.u.pid = start_userspace(stack);
  71         unblock_signals_trace();
  72 
  73         if (to_mm->id.u.pid < 0) {
  74                 ret = to_mm->id.u.pid;
  75                 goto out_free;
  76         }
  77 
  78         ret = init_new_ldt(to_mm, from_mm);
  79         if (ret < 0) {
  80                 printk(KERN_ERR "init_new_context_skas - init_ldt"
  81                        " failed, errno = %d\n", ret);
  82                 goto out_free;
  83         }
  84 
  85         return 0;
  86 
  87  out_free:
  88         if (to_mm->id.stack != 0)
  89                 free_page(to_mm->id.stack);
  90  out:
  91         return ret;
  92 }
  93 
  94 void uml_setup_stubs(struct mm_struct *mm)
  95 {
  96         int err, ret;
  97 
  98         ret = init_stub_pte(mm, STUB_CODE,
  99                             (unsigned long) __syscall_stub_start);
 100         if (ret)
 101                 goto out;
 102 
 103         ret = init_stub_pte(mm, STUB_DATA, mm->context.id.stack);
 104         if (ret)
 105                 goto out;
 106 
 107         mm->context.stub_pages[0] = virt_to_page(__syscall_stub_start);
 108         mm->context.stub_pages[1] = virt_to_page(mm->context.id.stack);
 109 
 110         /* dup_mmap already holds mmap_sem */
 111         err = install_special_mapping(mm, STUB_START, STUB_END - STUB_START,
 112                                       VM_READ | VM_MAYREAD | VM_EXEC |
 113                                       VM_MAYEXEC | VM_DONTCOPY | VM_PFNMAP,
 114                                       mm->context.stub_pages);
 115         if (err) {
 116                 printk(KERN_ERR "install_special_mapping returned %d\n", err);
 117                 goto out;
 118         }
 119         return;
 120 
 121 out:
 122         force_sigsegv(SIGSEGV);
 123 }
 124 
 125 void arch_exit_mmap(struct mm_struct *mm)
 126 {
 127         pte_t *pte;
 128 
 129         pte = virt_to_pte(mm, STUB_CODE);
 130         if (pte != NULL)
 131                 pte_clear(mm, STUB_CODE, pte);
 132 
 133         pte = virt_to_pte(mm, STUB_DATA);
 134         if (pte == NULL)
 135                 return;
 136 
 137         pte_clear(mm, STUB_DATA, pte);
 138 }
 139 
 140 void destroy_context(struct mm_struct *mm)
 141 {
 142         struct mm_context *mmu = &mm->context;
 143 
 144         /*
 145          * If init_new_context wasn't called, this will be
 146          * zero, resulting in a kill(0), which will result in the
 147          * whole UML suddenly dying.  Also, cover negative and
 148          * 1 cases, since they shouldn't happen either.
 149          */
 150         if (mmu->id.u.pid < 2) {
 151                 printk(KERN_ERR "corrupt mm_context - pid = %d\n",
 152                        mmu->id.u.pid);
 153                 return;
 154         }
 155         os_kill_ptraced_process(mmu->id.u.pid, 1);
 156 
 157         free_page(mmu->id.stack);
 158         free_ldt(mmu);
 159 }