arch/x86/boot/compressed/pagetable.c

   1 /*
   2  * This code is used on x86_64 to create page table identity mappings on
   3  * demand by building up a new set of page tables (or appending to the
   4  * existing ones), and then switching over to them when ready.
   5  *
   6  * Copyright (C) 2015-2016  Yinghai Lu
   7  * Copyright (C)      2016  Kees Cook
   8  */
   9
  10 /*
  11  * Since we're dealing with identity mappings, physical and virtual
  12  * addresses are the same, so override these defines which are ultimately
  13  * used by the headers in misc.h.
  14  */
  15 #define __pa(x)  ((unsigned long)(x))
  16 #define __va(x)  ((void *)((unsigned long)(x)))
  17
  18 #include "misc.h"
  19
  20 /* These actually do the work of building the kernel identity maps. */
  21 #include <asm/init.h>
  22 #include <asm/pgtable.h>
  23 /* Use the static base for this part of the boot process */
  24 #undef __PAGE_OFFSET
  25 #define __PAGE_OFFSET __PAGE_OFFSET_BASE
  26 #include "../../mm/ident_map.c"
  27
  28 /* Used by pgtable.h asm code to force instruction serialization. */
  29 unsigned long __force_order;
  30
  31 /* Used to track our page table allocation area. */
  32 struct alloc_pgt_data {
  33         unsigned char *pgt_buf;
  34         unsigned long pgt_buf_size;
  35         unsigned long pgt_buf_offset;
  36 };
  37
  38 /*
  39  * Allocates space for a page table entry, using struct alloc_pgt_data
  40  * above. Besides the local callers, this is used as the allocation
  41  * callback in mapping_info below.
  42  */
  43 static void *alloc_pgt_page(void *context)
  44 {
  45         struct alloc_pgt_data *pages = (struct alloc_pgt_data *)context;
  46         unsigned char *entry;
  47
  48         /* Validate there is space available for a new page. */
  49         if (pages->pgt_buf_offset >= pages->pgt_buf_size) {
  50                 debug_putstr("out of pgt_buf in " __FILE__ "!?\n");
  51                 debug_putaddr(pages->pgt_buf_offset);
  52                 debug_putaddr(pages->pgt_buf_size);
  53                 return NULL;
  54         }
  55
  56         entry = pages->pgt_buf + pages->pgt_buf_offset;
  57         pages->pgt_buf_offset += PAGE_SIZE;
  58
  59         return entry;
  60 }
  61
  62 /* Used to track our allocated page tables. */
  63 static struct alloc_pgt_data pgt_data;
  64
  65 /* The top level page table entry pointer. */
  66 static unsigned long level4p;
  67
  68 /*
  69  * Mapping information structure passed to kernel_ident_mapping_init().
  70  * Due to relocation, pointers must be assigned at run time not build time.
  71  */
  72 static struct x86_mapping_info mapping_info = {
  73         .page_flag       = __PAGE_KERNEL_LARGE_EXEC,
  74 };
  75
  76 /* Locates and clears a region for a new top level page table. */
  77 void initialize_identity_maps(void)
  78 {
  79         /* Init mapping_info with run-time function/buffer pointers. */
  80         mapping_info.alloc_pgt_page = alloc_pgt_page;
  81         mapping_info.context = &pgt_data;
  82
  83         /*
  84          * It should be impossible for this not to already be true,
  85          * but since calling this a second time would rewind the other
  86          * counters, let's just make sure this is reset too.
  87          */
  88         pgt_data.pgt_buf_offset = 0;
  89
  90         /*
  91          * If we came here via startup_32(), cr3 will be _pgtable already
  92          * and we must append to the existing area instead of entirely
  93          * overwriting it.
  94          */
  95         level4p = read_cr3();
  96         if (level4p == (unsigned long)_pgtable) {
  97                 debug_putstr("booted via startup_32()\n");
  98                 pgt_data.pgt_buf = _pgtable + BOOT_INIT_PGT_SIZE;
  99                 pgt_data.pgt_buf_size = BOOT_PGT_SIZE - BOOT_INIT_PGT_SIZE;
 100                 memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
 101         } else {
 102                 debug_putstr("booted via startup_64()\n");
 103                 pgt_data.pgt_buf = _pgtable;
 104                 pgt_data.pgt_buf_size = BOOT_PGT_SIZE;
 105                 memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
 106                 level4p = (unsigned long)alloc_pgt_page(&pgt_data);
 107         }
 108 }
 109
 110 /*
 111  * Adds the specified range to what will become the new identity mappings.
 112  * Once all ranges have been added, the new mapping is activated by calling
 113  * finalize_identity_maps() below.
 114  */
 115 void add_identity_map(unsigned long start, unsigned long size)
 116 {
 117         unsigned long end = start + size;
 118
 119         /* Align boundary to 2M. */
 120         start = round_down(start, PMD_SIZE);
 121         end = round_up(end, PMD_SIZE);
 122         if (start >= end)
 123                 return;
 124
 125         /* Build the mapping. */
 126         kernel_ident_mapping_init(&mapping_info, (pgd_t *)level4p,
 127                                   start, end);
 128 }
 129
 130 /*
 131  * This switches the page tables to the new level4 that has been built
 132  * via calls to add_identity_map() above. If booted via startup_32(),
 133  * this is effectively a no-op.
 134  */
 135 void finalize_identity_maps(void)
 136 {
 137         write_cr3(level4p);
 138 }