arch/x86/purgatory/purgatory.c

   1 /*
   2  * purgatory: Runs between two kernels
   3  *
   4  * Copyright (C) 2014 Red Hat Inc.
   5  *
   6  * Author:
   7  *       Vivek Goyal <vgoyal@redhat.com>
   8  *
   9  * This source code is licensed under the GNU General Public License,
  10  * Version 2.  See the file COPYING for more details.
  11  */
  12
  13 #include "sha256.h"
  14 #include "../boot/string.h"
  15
  16 struct sha_region {
  17         unsigned long start;
  18         unsigned long len;
  19 };
  20
  21 unsigned long backup_dest = 0;
  22 unsigned long backup_src = 0;
  23 unsigned long backup_sz = 0;
  24
  25 u8 sha256_digest[SHA256_DIGEST_SIZE] = { 0 };
  26
  27 struct sha_region sha_regions[16] = {};
  28
  29 /*
  30  * On x86, second kernel requries first 640K of memory to boot. Copy
  31  * first 640K to a backup region in reserved memory range so that second
  32  * kernel can use first 640K.
  33  */
  34 static int copy_backup_region(void)
  35 {
  36         if (backup_dest)
  37                 memcpy((void *)backup_dest, (void *)backup_src, backup_sz);
  38
  39         return 0;
  40 }
  41
  42 int verify_sha256_digest(void)
  43 {
  44         struct sha_region *ptr, *end;
  45         u8 digest[SHA256_DIGEST_SIZE];
  46         struct sha256_state sctx;
  47
  48         sha256_init(&sctx);
  49         end = &sha_regions[sizeof(sha_regions)/sizeof(sha_regions[0])];
  50         for (ptr = sha_regions; ptr < end; ptr++)
  51                 sha256_update(&sctx, (uint8_t *)(ptr->start), ptr->len);
  52
  53         sha256_final(&sctx, digest);
  54
  55         if (memcmp(digest, sha256_digest, sizeof(digest)))
  56                 return 1;
  57
  58         return 0;
  59 }
  60
  61 void purgatory(void)
  62 {
  63         int ret;
  64
  65         ret = verify_sha256_digest();
  66         if (ret) {
  67                 /* loop forever */
  68                 for (;;)
  69                         ;
  70         }
  71         copy_backup_region();
  72 }