drivers/firmware/efi/libstub/tpm.c

   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 /*
  24  * Enable reboot attack mitigation. This requests that the firmware clear the
  25  * RAM on next reboot before proceeding with boot, ensuring that any secrets
  26  * are cleared. If userland has ensured that all secrets have been removed
  27  * from RAM before reboot it can simply reset this variable.
  28  */
  29 void efi_enable_reset_attack_mitigation(void)
  30 {
  31         u8 val = 1;
  32         efi_guid_t var_guid = MEMORY_ONLY_RESET_CONTROL_GUID;
  33         efi_status_t status;
  34         unsigned long datasize = 0;
  35
  36         status = get_efi_var(efi_MemoryOverWriteRequest_name, &var_guid,
  37                              NULL, &datasize, NULL);
  38
  39         if (status == EFI_NOT_FOUND)
  40                 return;
  41
  42         set_efi_var(efi_MemoryOverWriteRequest_name, &var_guid,
  43                     EFI_VARIABLE_NON_VOLATILE |
  44                     EFI_VARIABLE_BOOTSERVICE_ACCESS |
  45                     EFI_VARIABLE_RUNTIME_ACCESS, sizeof(val), &val);
  46 }
  47
  48 #endif
  49
  50 void efi_retrieve_tpm2_eventlog(void)
  51 {
  52         efi_guid_t tcg2_guid = EFI_TCG2_PROTOCOL_GUID;
  53         efi_guid_t linux_eventlog_guid = LINUX_EFI_TPM_EVENT_LOG_GUID;
  54         efi_status_t status;
  55         efi_physical_addr_t log_location = 0, log_last_entry = 0;
  56         struct linux_efi_tpm_eventlog *log_tbl = NULL;
  57         struct efi_tcg2_final_events_table *final_events_table = NULL;
  58         unsigned long first_entry_addr, last_entry_addr;
  59         size_t log_size, last_entry_size;
  60         efi_bool_t truncated;
  61         int version = EFI_TCG2_EVENT_LOG_FORMAT_TCG_2;
  62         efi_tcg2_protocol_t *tcg2_protocol = NULL;
  63         int final_events_size = 0;
  64
  65         status = efi_bs_call(locate_protocol, &tcg2_guid, NULL,
  66                              (void **)&tcg2_protocol);
  67         if (status != EFI_SUCCESS)
  68                 return;
  69
  70         status = efi_call_proto(tcg2_protocol, get_event_log, version,
  71                                 &log_location, &log_last_entry, &truncated);
  72
  73         if (status != EFI_SUCCESS || !log_location) {
  74                 version = EFI_TCG2_EVENT_LOG_FORMAT_TCG_1_2;
  75                 status = efi_call_proto(tcg2_protocol, get_event_log, version,
  76                                         &log_location, &log_last_entry,
  77                                         &truncated);
  78                 if (status != EFI_SUCCESS || !log_location)
  79                         return;
  80
  81         }
  82
  83         first_entry_addr = (unsigned long) log_location;
  84
  85         /*
  86          * We populate the EFI table even if the logs are empty.
  87          */
  88         if (!log_last_entry) {
  89                 log_size = 0;
  90         } else {
  91                 last_entry_addr = (unsigned long) log_last_entry;
  92                 /*
  93                  * get_event_log only returns the address of the last entry.
  94                  * We need to calculate its size to deduce the full size of
  95                  * the logs.
  96                  */
  97                 if (version == EFI_TCG2_EVENT_LOG_FORMAT_TCG_2) {
  98                         /*
  99                          * The TCG2 log format has variable length entries,
 100                          * and the information to decode the hash algorithms
 101                          * back into a size is contained in the first entry -
 102                          * pass a pointer to the final entry (to calculate its
 103                          * size) and the first entry (so we know how long each
 104                          * digest is)
 105                          */
 106                         last_entry_size =
 107                                 __calc_tpm2_event_size((void *)last_entry_addr,
 108                                                     (void *)(long)log_location,
 109                                                     false);
 110                 } else {
 111                         last_entry_size = sizeof(struct tcpa_event) +
 112                            ((struct tcpa_event *) last_entry_addr)->event_size;
 113                 }
 114                 log_size = log_last_entry - log_location + last_entry_size;
 115         }
 116
 117         /* Allocate space for the logs and copy them. */
 118         status = efi_bs_call(allocate_pool, EFI_LOADER_DATA,
 119                              sizeof(*log_tbl) + log_size, (void **)&log_tbl);
 120
 121         if (status != EFI_SUCCESS) {
 122                 efi_err("Unable to allocate memory for event log\n");
 123                 return;
 124         }
 125
 126         /*
 127          * Figure out whether any events have already been logged to the
 128          * final events structure, and if so how much space they take up
 129          */
 130         if (version == EFI_TCG2_EVENT_LOG_FORMAT_TCG_2)
 131                 final_events_table = get_efi_config_table(LINUX_EFI_TPM_FINAL_LOG_GUID);
 132         if (final_events_table && final_events_table->nr_events) {
 133                 struct tcg_pcr_event2_head *header;
 134                 int offset;
 135                 void *data;
 136                 int event_size;
 137                 int i = final_events_table->nr_events;
 138
 139                 data = (void *)final_events_table;
 140                 offset = sizeof(final_events_table->version) +
 141                         sizeof(final_events_table->nr_events);
 142
 143                 while (i > 0) {
 144                         header = data + offset + final_events_size;
 145                         event_size = __calc_tpm2_event_size(header,
 146                                                    (void *)(long)log_location,
 147                                                    false);
 148                         final_events_size += event_size;
 149                         i--;
 150                 }
 151         }
 152
 153         memset(log_tbl, 0, sizeof(*log_tbl) + log_size);
 154         log_tbl->size = log_size;
 155         log_tbl->final_events_preboot_size = final_events_size;
 156         log_tbl->version = version;
 157         memcpy(log_tbl->log, (void *) first_entry_addr, log_size);
 158
 159         status = efi_bs_call(install_configuration_table,
 160                              &linux_eventlog_guid, log_tbl);
 161         if (status != EFI_SUCCESS)
 162                 goto err_free;
 163         return;
 164
 165 err_free:
 166         efi_bs_call(free_pool, log_tbl);
 167 }