arch/x86/boot/compressed/pagetable.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * This code is used on x86_64 to create page table identity mappings on
   4  * demand by building up a new set of page tables (or appending to the
   5  * existing ones), and then switching over to them when ready.
   6  *
   7  * Copyright (C) 2015-2016  Yinghai Lu
   8  * Copyright (C)      2016  Kees Cook
   9  */
  10
  11 /*
  12  * Since we're dealing with identity mappings, physical and virtual
  13  * addresses are the same, so override these defines which are ultimately
  14  * used by the headers in misc.h.
  15  */
  16 #define __pa(x)  ((unsigned long)(x))
  17 #define __va(x)  ((void *)((unsigned long)(x)))
  18
  19 /*
  20  * The pgtable.h and mm/ident_map.c includes make use of the SME related
  21  * information which is not used in the compressed image support. Un-define
  22  * the SME support to avoid any compile and link errors.
  23  */
  24 #undef CONFIG_AMD_MEM_ENCRYPT
  25
  26 /* No PAGE_TABLE_ISOLATION support needed either: */
  27 #undef CONFIG_PAGE_TABLE_ISOLATION
  28
  29 #include "misc.h"
  30
  31 /* These actually do the work of building the kernel identity maps. */
  32 #include <asm/init.h>
  33 #include <asm/pgtable.h>
  34 /* Use the static base for this part of the boot process */
  35 #undef __PAGE_OFFSET
  36 #define __PAGE_OFFSET __PAGE_OFFSET_BASE
  37 #include "../../mm/ident_map.c"
  38
  39 /* Used by pgtable.h asm code to force instruction serialization. */
  40 unsigned long __force_order;
  41
  42 /* Used to track our page table allocation area. */
  43 struct alloc_pgt_data {
  44         unsigned char *pgt_buf;
  45         unsigned long pgt_buf_size;
  46         unsigned long pgt_buf_offset;
  47 };
  48
  49 /*
  50  * Allocates space for a page table entry, using struct alloc_pgt_data
  51  * above. Besides the local callers, this is used as the allocation
  52  * callback in mapping_info below.
  53  */
  54 static void *alloc_pgt_page(void *context)
  55 {
  56         struct alloc_pgt_data *pages = (struct alloc_pgt_data *)context;
  57         unsigned char *entry;
  58
  59         /* Validate there is space available for a new page. */
  60         if (pages->pgt_buf_offset >= pages->pgt_buf_size) {
  61                 debug_putstr("out of pgt_buf in " __FILE__ "!?\n");
  62                 debug_putaddr(pages->pgt_buf_offset);
  63                 debug_putaddr(pages->pgt_buf_size);
  64                 return NULL;
  65         }
  66
  67         entry = pages->pgt_buf + pages->pgt_buf_offset;
  68         pages->pgt_buf_offset += PAGE_SIZE;
  69
  70         return entry;
  71 }
  72
  73 /* Used to track our allocated page tables. */
  74 static struct alloc_pgt_data pgt_data;
  75
  76 /* The top level page table entry pointer. */
  77 static unsigned long top_level_pgt;
  78
  79 /*
  80  * Mapping information structure passed to kernel_ident_mapping_init().
  81  * Due to relocation, pointers must be assigned at run time not build time.
  82  */
  83 static struct x86_mapping_info mapping_info = {
  84         .page_flag       = __PAGE_KERNEL_LARGE_EXEC,
  85 };
  86
  87 /* Locates and clears a region for a new top level page table. */
  88 void initialize_identity_maps(void)
  89 {
  90         /* Init mapping_info with run-time function/buffer pointers. */
  91         mapping_info.alloc_pgt_page = alloc_pgt_page;
  92         mapping_info.context = &pgt_data;
  93
  94         /*
  95          * It should be impossible for this not to already be true,
  96          * but since calling this a second time would rewind the other
  97          * counters, let's just make sure this is reset too.
  98          */
  99         pgt_data.pgt_buf_offset = 0;
 100
 101         /*
 102          * If we came here via startup_32(), cr3 will be _pgtable already
 103          * and we must append to the existing area instead of entirely
 104          * overwriting it.
 105          *
 106          * With 5-level paging, we use '_pgtable' to allocate the p4d page table,
 107          * the top-level page table is allocated separately.
 108          *
 109          * p4d_offset(top_level_pgt, 0) would cover both the 4- and 5-level
 110          * cases. On 4-level paging it's equal to 'top_level_pgt'.
 111          */
 112         top_level_pgt = read_cr3_pa();
 113         if (p4d_offset((pgd_t *)top_level_pgt, 0) == (p4d_t *)_pgtable) {
 114                 debug_putstr("booted via startup_32()\n");
 115                 pgt_data.pgt_buf = _pgtable + BOOT_INIT_PGT_SIZE;
 116                 pgt_data.pgt_buf_size = BOOT_PGT_SIZE - BOOT_INIT_PGT_SIZE;
 117                 memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
 118         } else {
 119                 debug_putstr("booted via startup_64()\n");
 120                 pgt_data.pgt_buf = _pgtable;
 121                 pgt_data.pgt_buf_size = BOOT_PGT_SIZE;
 122                 memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
 123                 top_level_pgt = (unsigned long)alloc_pgt_page(&pgt_data);
 124         }
 125 }
 126
 127 /*
 128  * Adds the specified range to what will become the new identity mappings.
 129  * Once all ranges have been added, the new mapping is activated by calling
 130  * finalize_identity_maps() below.
 131  */
 132 void add_identity_map(unsigned long start, unsigned long size)
 133 {
 134         unsigned long end = start + size;
 135
 136         /* Align boundary to 2M. */
 137         start = round_down(start, PMD_SIZE);
 138         end = round_up(end, PMD_SIZE);
 139         if (start >= end)
 140                 return;
 141
 142         /* Build the mapping. */
 143         kernel_ident_mapping_init(&mapping_info, (pgd_t *)top_level_pgt,
 144                                   start, end);
 145 }
 146
 147 /*
 148  * This switches the page tables to the new level4 that has been built
 149  * via calls to add_identity_map() above. If booted via startup_32(),
 150  * this is effectively a no-op.
 151  */
 152 void finalize_identity_maps(void)
 153 {
 154         write_cr3(top_level_pgt);
 155 }