arch/x86/include/asm/bootparam_utils.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef _ASM_X86_BOOTPARAM_UTILS_H
   3 #define _ASM_X86_BOOTPARAM_UTILS_H
   4
   5 #include <asm/bootparam.h>
   6
   7 /*
   8  * This file is included from multiple environments.  Do not
   9  * add completing #includes to make it standalone.
  10  */
  11
  12 /*
  13  * Deal with bootloaders which fail to initialize unknown fields in
  14  * boot_params to zero.  The list fields in this list are taken from
  15  * analysis of kexec-tools; if other broken bootloaders initialize a
  16  * different set of fields we will need to figure out how to disambiguate.
  17  *
  18  * Note: efi_info is commonly left uninitialized, but that field has a
  19  * private magic, so it is better to leave it unchanged.
  20  */
  21
  22 #define sizeof_mbr(type, member) ({ sizeof(((type *)0)->member); })
  23
  24 #define BOOT_PARAM_PRESERVE(struct_member)                              \
  25         {                                                               \
  26                 .start = offsetof(struct boot_params, struct_member),   \
  27                 .len   = sizeof_mbr(struct boot_params, struct_member), \
  28         }
  29
  30 struct boot_params_to_save {
  31         unsigned int start;
  32         unsigned int len;
  33 };
  34
  35 static void sanitize_boot_params(struct boot_params *boot_params)
  36 {
  37         /*
  38          * IMPORTANT NOTE TO BOOTLOADER AUTHORS: do not simply clear
  39          * this field.  The purpose of this field is to guarantee
  40          * compliance with the x86 boot spec located in
  41          * Documentation/x86/boot.rst .  That spec says that the
  42          * *whole* structure should be cleared, after which only the
  43          * portion defined by struct setup_header (boot_params->hdr)
  44          * should be copied in.
  45          *
  46          * If you're having an issue because the sentinel is set, you
  47          * need to change the whole structure to be cleared, not this
  48          * (or any other) individual field, or you will soon have
  49          * problems again.
  50          */
  51         if (boot_params->sentinel) {
  52                 static struct boot_params scratch;
  53                 char *bp_base = (char *)boot_params;
  54                 char *save_base = (char *)&scratch;
  55                 int i;
  56
  57                 const struct boot_params_to_save to_save[] = {
  58                         BOOT_PARAM_PRESERVE(screen_info),
  59                         BOOT_PARAM_PRESERVE(apm_bios_info),
  60                         BOOT_PARAM_PRESERVE(tboot_addr),
  61                         BOOT_PARAM_PRESERVE(ist_info),
  62                         BOOT_PARAM_PRESERVE(hd0_info),
  63                         BOOT_PARAM_PRESERVE(hd1_info),
  64                         BOOT_PARAM_PRESERVE(sys_desc_table),
  65                         BOOT_PARAM_PRESERVE(olpc_ofw_header),
  66                         BOOT_PARAM_PRESERVE(efi_info),
  67                         BOOT_PARAM_PRESERVE(alt_mem_k),
  68                         BOOT_PARAM_PRESERVE(scratch),
  69                         BOOT_PARAM_PRESERVE(e820_entries),
  70                         BOOT_PARAM_PRESERVE(eddbuf_entries),
  71                         BOOT_PARAM_PRESERVE(edd_mbr_sig_buf_entries),
  72                         BOOT_PARAM_PRESERVE(edd_mbr_sig_buffer),
  73                         BOOT_PARAM_PRESERVE(secure_boot),
  74                         BOOT_PARAM_PRESERVE(hdr),
  75                         BOOT_PARAM_PRESERVE(e820_table),
  76                         BOOT_PARAM_PRESERVE(eddbuf),
  77                 };
  78
  79                 memset(&scratch, 0, sizeof(scratch));
  80
  81                 for (i = 0; i < ARRAY_SIZE(to_save); i++) {
  82                         memcpy(save_base + to_save[i].start,
  83                                bp_base + to_save[i].start, to_save[i].len);
  84                 }
  85
  86                 memcpy(boot_params, save_base, sizeof(*boot_params));
  87         }
  88 }
  89
  90 #endif /* _ASM_X86_BOOTPARAM_UTILS_H */