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 /*
  19  * The pgtable.h and mm/ident_map.c includes make use of the SME related
  20  * information which is not used in the compressed image support. Un-define
  21  * the SME support to avoid any compile and link errors.
  22  */
  23 #undef CONFIG_AMD_MEM_ENCRYPT
  24
  25 #include "misc.h"
  26
  27 /* These actually do the work of building the kernel identity maps. */
  28 #include <asm/init.h>
  29 #include <asm/pgtable.h>
  30 /* Use the static base for this part of the boot process */
  31 #undef __PAGE_OFFSET
  32 #define __PAGE_OFFSET __PAGE_OFFSET_BASE
  33 #include "../../mm/ident_map.c"
  34
  35 /* Used by pgtable.h asm code to force instruction serialization. */
  36 unsigned long __force_order;
  37
  38 /* Used to track our page table allocation area. */
  39 struct alloc_pgt_data {
  40         unsigned char *pgt_buf;
  41         unsigned long pgt_buf_size;
  42         unsigned long pgt_buf_offset;
  43 };
  44
  45 /*
  46  * Allocates space for a page table entry, using struct alloc_pgt_data
  47  * above. Besides the local callers, this is used as the allocation
  48  * callback in mapping_info below.
  49  */
  50 static void *alloc_pgt_page(void *context)
  51 {
  52         struct alloc_pgt_data *pages = (struct alloc_pgt_data *)context;
  53         unsigned char *entry;
  54
  55         /* Validate there is space available for a new page. */
  56         if (pages->pgt_buf_offset >= pages->pgt_buf_size) {
  57                 debug_putstr("out of pgt_buf in " __FILE__ "!?\n");
  58                 debug_putaddr(pages->pgt_buf_offset);
  59                 debug_putaddr(pages->pgt_buf_size);
  60                 return NULL;
  61         }
  62
  63         entry = pages->pgt_buf + pages->pgt_buf_offset;
  64         pages->pgt_buf_offset += PAGE_SIZE;
  65
  66         return entry;
  67 }
  68
  69 /* Used to track our allocated page tables. */
  70 static struct alloc_pgt_data pgt_data;
  71
  72 /* The top level page table entry pointer. */
  73 static unsigned long top_level_pgt;
  74
  75 /*
  76  * Mapping information structure passed to kernel_ident_mapping_init().
  77  * Due to relocation, pointers must be assigned at run time not build time.
  78  */
  79 static struct x86_mapping_info mapping_info = {
  80         .page_flag       = __PAGE_KERNEL_LARGE_EXEC,
  81 };
  82
  83 /* Locates and clears a region for a new top level page table. */
  84 void initialize_identity_maps(void)
  85 {
  86         /* Init mapping_info with run-time function/buffer pointers. */
  87         mapping_info.alloc_pgt_page = alloc_pgt_page;
  88         mapping_info.context = &pgt_data;
  89
  90         /*
  91          * It should be impossible for this not to already be true,
  92          * but since calling this a second time would rewind the other
  93          * counters, let's just make sure this is reset too.
  94          */
  95         pgt_data.pgt_buf_offset = 0;
  96
  97         /*
  98          * If we came here via startup_32(), cr3 will be _pgtable already
  99          * and we must append to the existing area instead of entirely
 100          * overwriting it.
 101          *
 102          * With 5-level paging, we use '_pgtable' to allocate the p4d page table,
 103          * the top-level page table is allocated separately.
 104          *
 105          * p4d_offset(top_level_pgt, 0) would cover both the 4- and 5-level
 106          * cases. On 4-level paging it's equal to 'top_level_pgt'.
 107          */
 108         top_level_pgt = read_cr3_pa();
 109         if (p4d_offset((pgd_t *)top_level_pgt, 0) == (p4d_t *)_pgtable) {
 110                 debug_putstr("booted via startup_32()\n");
 111                 pgt_data.pgt_buf = _pgtable + BOOT_INIT_PGT_SIZE;
 112                 pgt_data.pgt_buf_size = BOOT_PGT_SIZE - BOOT_INIT_PGT_SIZE;
 113                 memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
 114         } else {
 115                 debug_putstr("booted via startup_64()\n");
 116                 pgt_data.pgt_buf = _pgtable;
 117                 pgt_data.pgt_buf_size = BOOT_PGT_SIZE;
 118                 memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
 119                 top_level_pgt = (unsigned long)alloc_pgt_page(&pgt_data);
 120         }
 121 }
 122
 123 /*
 124  * Adds the specified range to what will become the new identity mappings.
 125  * Once all ranges have been added, the new mapping is activated by calling
 126  * finalize_identity_maps() below.
 127  */
 128 void add_identity_map(unsigned long start, unsigned long size)
 129 {
 130         unsigned long end = start + size;
 131
 132         /* Align boundary to 2M. */
 133         start = round_down(start, PMD_SIZE);
 134         end = round_up(end, PMD_SIZE);
 135         if (start >= end)
 136                 return;
 137
 138         /* Build the mapping. */
 139         kernel_ident_mapping_init(&mapping_info, (pgd_t *)top_level_pgt,
 140                                   start, end);
 141 }
 142
 143 /*
 144  * This switches the page tables to the new level4 that has been built
 145  * via calls to add_identity_map() above. If booted via startup_32(),
 146  * this is effectively a no-op.
 147  */
 148 void finalize_identity_maps(void)
 149 {
 150         write_cr3(top_level_pgt);
 151 }