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 */
91