xref: /openbmc/linux/drivers/firmware/efi/libstub/tpm.c (revision 9a8f3203)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * TPM handling.
4  *
5  * Copyright (C) 2016 CoreOS, Inc
6  * Copyright (C) 2017 Google, Inc.
7  *     Matthew Garrett <mjg59@google.com>
8  *     Thiebaud Weksteen <tweek@google.com>
9  */
10 #include <linux/efi.h>
11 #include <linux/tpm_eventlog.h>
12 #include <asm/efi.h>
13 
14 #include "efistub.h"
15 
16 #ifdef CONFIG_RESET_ATTACK_MITIGATION
17 static const efi_char16_t efi_MemoryOverWriteRequest_name[] =
18 	L"MemoryOverwriteRequestControl";
19 
20 #define MEMORY_ONLY_RESET_CONTROL_GUID \
21 	EFI_GUID(0xe20939be, 0x32d4, 0x41be, 0xa1, 0x50, 0x89, 0x7f, 0x85, 0xd4, 0x98, 0x29)
22 
23 #define get_efi_var(name, vendor, ...) \
24 	efi_call_runtime(get_variable, \
25 			 (efi_char16_t *)(name), (efi_guid_t *)(vendor), \
26 			 __VA_ARGS__)
27 
28 #define set_efi_var(name, vendor, ...) \
29 	efi_call_runtime(set_variable, \
30 			 (efi_char16_t *)(name), (efi_guid_t *)(vendor), \
31 			 __VA_ARGS__)
32 
33 /*
34  * Enable reboot attack mitigation. This requests that the firmware clear the
35  * RAM on next reboot before proceeding with boot, ensuring that any secrets
36  * are cleared. If userland has ensured that all secrets have been removed
37  * from RAM before reboot it can simply reset this variable.
38  */
39 void efi_enable_reset_attack_mitigation(efi_system_table_t *sys_table_arg)
40 {
41 	u8 val = 1;
42 	efi_guid_t var_guid = MEMORY_ONLY_RESET_CONTROL_GUID;
43 	efi_status_t status;
44 	unsigned long datasize = 0;
45 
46 	status = get_efi_var(efi_MemoryOverWriteRequest_name, &var_guid,
47 			     NULL, &datasize, NULL);
48 
49 	if (status == EFI_NOT_FOUND)
50 		return;
51 
52 	set_efi_var(efi_MemoryOverWriteRequest_name, &var_guid,
53 		    EFI_VARIABLE_NON_VOLATILE |
54 		    EFI_VARIABLE_BOOTSERVICE_ACCESS |
55 		    EFI_VARIABLE_RUNTIME_ACCESS, sizeof(val), &val);
56 }
57 
58 #endif
59 
60 static void efi_retrieve_tpm2_eventlog_1_2(efi_system_table_t *sys_table_arg)
61 {
62 	efi_guid_t tcg2_guid = EFI_TCG2_PROTOCOL_GUID;
63 	efi_guid_t linux_eventlog_guid = LINUX_EFI_TPM_EVENT_LOG_GUID;
64 	efi_status_t status;
65 	efi_physical_addr_t log_location = 0, log_last_entry = 0;
66 	struct linux_efi_tpm_eventlog *log_tbl = NULL;
67 	unsigned long first_entry_addr, last_entry_addr;
68 	size_t log_size, last_entry_size;
69 	efi_bool_t truncated;
70 	void *tcg2_protocol = NULL;
71 
72 	status = efi_call_early(locate_protocol, &tcg2_guid, NULL,
73 				&tcg2_protocol);
74 	if (status != EFI_SUCCESS)
75 		return;
76 
77 	status = efi_call_proto(efi_tcg2_protocol, get_event_log, tcg2_protocol,
78 				EFI_TCG2_EVENT_LOG_FORMAT_TCG_1_2,
79 				&log_location, &log_last_entry, &truncated);
80 	if (status != EFI_SUCCESS)
81 		return;
82 
83 	if (!log_location)
84 		return;
85 	first_entry_addr = (unsigned long) log_location;
86 
87 	/*
88 	 * We populate the EFI table even if the logs are empty.
89 	 */
90 	if (!log_last_entry) {
91 		log_size = 0;
92 	} else {
93 		last_entry_addr = (unsigned long) log_last_entry;
94 		/*
95 		 * get_event_log only returns the address of the last entry.
96 		 * We need to calculate its size to deduce the full size of
97 		 * the logs.
98 		 */
99 		last_entry_size = sizeof(struct tcpa_event) +
100 			((struct tcpa_event *) last_entry_addr)->event_size;
101 		log_size = log_last_entry - log_location + last_entry_size;
102 	}
103 
104 	/* Allocate space for the logs and copy them. */
105 	status = efi_call_early(allocate_pool, EFI_LOADER_DATA,
106 				sizeof(*log_tbl) + log_size,
107 				(void **) &log_tbl);
108 
109 	if (status != EFI_SUCCESS) {
110 		efi_printk(sys_table_arg,
111 			   "Unable to allocate memory for event log\n");
112 		return;
113 	}
114 
115 	memset(log_tbl, 0, sizeof(*log_tbl) + log_size);
116 	log_tbl->size = log_size;
117 	log_tbl->version = EFI_TCG2_EVENT_LOG_FORMAT_TCG_1_2;
118 	memcpy(log_tbl->log, (void *) first_entry_addr, log_size);
119 
120 	status = efi_call_early(install_configuration_table,
121 				&linux_eventlog_guid, log_tbl);
122 	if (status != EFI_SUCCESS)
123 		goto err_free;
124 	return;
125 
126 err_free:
127 	efi_call_early(free_pool, log_tbl);
128 }
129 
130 void efi_retrieve_tpm2_eventlog(efi_system_table_t *sys_table_arg)
131 {
132 	/* Only try to retrieve the logs in 1.2 format. */
133 	efi_retrieve_tpm2_eventlog_1_2(sys_table_arg);
134 }
135