arch/x86/boot/compressed/kaslr_64.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 /* No PAGE_TABLE_ISOLATION support needed either: */
  20 #undef CONFIG_PAGE_TABLE_ISOLATION
  21
  22 #include "misc.h"
  23
  24 /* These actually do the work of building the kernel identity maps. */
  25 #include <asm/init.h>
  26 #include <asm/pgtable.h>
  27 /* Use the static base for this part of the boot process */
  28 #undef __PAGE_OFFSET
  29 #define __PAGE_OFFSET __PAGE_OFFSET_BASE
  30 #include "../../mm/ident_map.c"
  31
  32 /* Used by pgtable.h asm code to force instruction serialization. */
  33 unsigned long __force_order;
  34
  35 /* Used to track our page table allocation area. */
  36 struct alloc_pgt_data {
  37         unsigned char *pgt_buf;
  38         unsigned long pgt_buf_size;
  39         unsigned long pgt_buf_offset;
  40 };
  41
  42 /*
  43  * Allocates space for a page table entry, using struct alloc_pgt_data
  44  * above. Besides the local callers, this is used as the allocation
  45  * callback in mapping_info below.
  46  */
  47 static void *alloc_pgt_page(void *context)
  48 {
  49         struct alloc_pgt_data *pages = (struct alloc_pgt_data *)context;
  50         unsigned char *entry;
  51
  52         /* Validate there is space available for a new page. */
  53         if (pages->pgt_buf_offset >= pages->pgt_buf_size) {
  54                 debug_putstr("out of pgt_buf in " __FILE__ "!?\n");
  55                 debug_putaddr(pages->pgt_buf_offset);
  56                 debug_putaddr(pages->pgt_buf_size);
  57                 return NULL;
  58         }
  59
  60         entry = pages->pgt_buf + pages->pgt_buf_offset;
  61         pages->pgt_buf_offset += PAGE_SIZE;
  62
  63         return entry;
  64 }
  65
  66 /* Used to track our allocated page tables. */
  67 static struct alloc_pgt_data pgt_data;
  68
  69 /* The top level page table entry pointer. */
  70 static unsigned long top_level_pgt;
  71
  72 phys_addr_t physical_mask = (1ULL << __PHYSICAL_MASK_SHIFT) - 1;
  73
  74 /*
  75  * Mapping information structure passed to kernel_ident_mapping_init().
  76  * Due to relocation, pointers must be assigned at run time not build time.
  77  */
  78 static struct x86_mapping_info mapping_info;
  79
  80 /* Locates and clears a region for a new top level page table. */
  81 void initialize_identity_maps(void)
  82 {
  83         /* If running as an SEV guest, the encryption mask is required. */
  84         set_sev_encryption_mask();
  85
  86         /* Exclude the encryption mask from __PHYSICAL_MASK */
  87         physical_mask &= ~sme_me_mask;
  88
  89         /* Init mapping_info with run-time function/buffer pointers. */
  90         mapping_info.alloc_pgt_page = alloc_pgt_page;
  91         mapping_info.context = &pgt_data;
  92         mapping_info.page_flag = __PAGE_KERNEL_LARGE_EXEC | sme_me_mask;
  93         mapping_info.kernpg_flag = _KERNPG_TABLE;
  94
  95         /*
  96          * It should be impossible for this not to already be true,
  97          * but since calling this a second time would rewind the other
  98          * counters, let's just make sure this is reset too.
  99          */
 100         pgt_data.pgt_buf_offset = 0;
 101
 102         /*
 103          * If we came here via startup_32(), cr3 will be _pgtable already
 104          * and we must append to the existing area instead of entirely
 105          * overwriting it.
 106          *
 107          * With 5-level paging, we use '_pgtable' to allocate the p4d page table,
 108          * the top-level page table is allocated separately.
 109          *
 110          * p4d_offset(top_level_pgt, 0) would cover both the 4- and 5-level
 111          * cases. On 4-level paging it's equal to 'top_level_pgt'.
 112          */
 113         top_level_pgt = read_cr3_pa();
 114         if (p4d_offset((pgd_t *)top_level_pgt, 0) == (p4d_t *)_pgtable) {
 115                 debug_putstr("booted via startup_32()\n");
 116                 pgt_data.pgt_buf = _pgtable + BOOT_INIT_PGT_SIZE;
 117                 pgt_data.pgt_buf_size = BOOT_PGT_SIZE - BOOT_INIT_PGT_SIZE;
 118                 memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
 119         } else {
 120                 debug_putstr("booted via startup_64()\n");
 121                 pgt_data.pgt_buf = _pgtable;
 122                 pgt_data.pgt_buf_size = BOOT_PGT_SIZE;
 123                 memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
 124                 top_level_pgt = (unsigned long)alloc_pgt_page(&pgt_data);
 125         }
 126 }
 127
 128 /*
 129  * Adds the specified range to what will become the new identity mappings.
 130  * Once all ranges have been added, the new mapping is activated by calling
 131  * finalize_identity_maps() below.
 132  */
 133 void add_identity_map(unsigned long start, unsigned long size)
 134 {
 135         unsigned long end = start + size;
 136
 137         /* Align boundary to 2M. */
 138         start = round_down(start, PMD_SIZE);
 139         end = round_up(end, PMD_SIZE);
 140         if (start >= end)
 141                 return;
 142
 143         /* Build the mapping. */
 144         kernel_ident_mapping_init(&mapping_info, (pgd_t *)top_level_pgt,
 145                                   start, end);
 146 }
 147
 148 /*
 149  * This switches the page tables to the new level4 that has been built
 150  * via calls to add_identity_map() above. If booted via startup_32(),
 151  * this is effectively a no-op.
 152  */
 153 void finalize_identity_maps(void)
 154 {
 155         write_cr3(top_level_pgt);
 156 }