arch/x86/purgatory/purgatory.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * purgatory: Runs between two kernels
   4  *
   5  * Copyright (C) 2014 Red Hat Inc.
   6  *
   7  * Author:
   8  *       Vivek Goyal <vgoyal@redhat.com>
   9  */
  10
  11 #include <linux/bug.h>
  12 #include <crypto/sha.h>
  13 #include <asm/purgatory.h>
  14
  15 #include "../boot/string.h"
  16
  17 unsigned long purgatory_backup_dest __section(.kexec-purgatory);
  18 unsigned long purgatory_backup_src __section(.kexec-purgatory);
  19 unsigned long purgatory_backup_sz __section(.kexec-purgatory);
  20
  21 u8 purgatory_sha256_digest[SHA256_DIGEST_SIZE] __section(.kexec-purgatory);
  22
  23 struct kexec_sha_region purgatory_sha_regions[KEXEC_SEGMENT_MAX] __section(.kexec-purgatory);
  24
  25 /*
  26  * On x86, second kernel requries first 640K of memory to boot. Copy
  27  * first 640K to a backup region in reserved memory range so that second
  28  * kernel can use first 640K.
  29  */
  30 static int copy_backup_region(void)
  31 {
  32         if (purgatory_backup_dest) {
  33                 memcpy((void *)purgatory_backup_dest,
  34                        (void *)purgatory_backup_src, purgatory_backup_sz);
  35         }
  36         return 0;
  37 }
  38
  39 static int verify_sha256_digest(void)
  40 {
  41         struct kexec_sha_region *ptr, *end;
  42         u8 digest[SHA256_DIGEST_SIZE];
  43         struct sha256_state sctx;
  44
  45         sha256_init(&sctx);
  46         end = purgatory_sha_regions + ARRAY_SIZE(purgatory_sha_regions);
  47
  48         for (ptr = purgatory_sha_regions; ptr < end; ptr++)
  49                 sha256_update(&sctx, (uint8_t *)(ptr->start), ptr->len);
  50
  51         sha256_final(&sctx, digest);
  52
  53         if (memcmp(digest, purgatory_sha256_digest, sizeof(digest)))
  54                 return 1;
  55
  56         return 0;
  57 }
  58
  59 void purgatory(void)
  60 {
  61         int ret;
  62
  63         ret = verify_sha256_digest();
  64         if (ret) {
  65                 /* loop forever */
  66                 for (;;)
  67                         ;
  68         }
  69         copy_backup_region();
  70 }
  71
  72 /*
  73  * Defined in order to reuse memcpy() and memset() from
  74  * arch/x86/boot/compressed/string.c
  75  */
  76 void warn(const char *msg) {}