drivers/firmware/efi/libstub/tpm.c

   1 /*
   2  * TPM handling.
   3  *
   4  * Copyright (C) 2016 CoreOS, Inc
   5  * Copyright (C) 2017 Google, Inc.
   6  *     Matthew Garrett <mjg59@google.com>
   7  *     Thiebaud Weksteen <tweek@google.com>
   8  *
   9  * This file is part of the Linux kernel, and is made available under the
  10  * terms of the GNU General Public License version 2.
  11  */
  12 #include <linux/efi.h>
  13 #include <linux/tpm_eventlog.h>
  14 #include <asm/efi.h>
  15
  16 #include "efistub.h"
  17
  18 #ifdef CONFIG_RESET_ATTACK_MITIGATION
  19 static const efi_char16_t efi_MemoryOverWriteRequest_name[] =
  20         L"MemoryOverwriteRequestControl";
  21
  22 #define MEMORY_ONLY_RESET_CONTROL_GUID \
  23         EFI_GUID(0xe20939be, 0x32d4, 0x41be, 0xa1, 0x50, 0x89, 0x7f, 0x85, 0xd4, 0x98, 0x29)
  24
  25 #define get_efi_var(name, vendor, ...) \
  26         efi_call_runtime(get_variable, \
  27                          (efi_char16_t *)(name), (efi_guid_t *)(vendor), \
  28                          __VA_ARGS__)
  29
  30 #define set_efi_var(name, vendor, ...) \
  31         efi_call_runtime(set_variable, \
  32                          (efi_char16_t *)(name), (efi_guid_t *)(vendor), \
  33                          __VA_ARGS__)
  34
  35 /*
  36  * Enable reboot attack mitigation. This requests that the firmware clear the
  37  * RAM on next reboot before proceeding with boot, ensuring that any secrets
  38  * are cleared. If userland has ensured that all secrets have been removed
  39  * from RAM before reboot it can simply reset this variable.
  40  */
  41 void efi_enable_reset_attack_mitigation(efi_system_table_t *sys_table_arg)
  42 {
  43         u8 val = 1;
  44         efi_guid_t var_guid = MEMORY_ONLY_RESET_CONTROL_GUID;
  45         efi_status_t status;
  46         unsigned long datasize = 0;
  47
  48         status = get_efi_var(efi_MemoryOverWriteRequest_name, &var_guid,
  49                              NULL, &datasize, NULL);
  50
  51         if (status == EFI_NOT_FOUND)
  52                 return;
  53
  54         set_efi_var(efi_MemoryOverWriteRequest_name, &var_guid,
  55                     EFI_VARIABLE_NON_VOLATILE |
  56                     EFI_VARIABLE_BOOTSERVICE_ACCESS |
  57                     EFI_VARIABLE_RUNTIME_ACCESS, sizeof(val), &val);
  58 }
  59
  60 #endif
  61
  62 static void efi_retrieve_tpm2_eventlog_1_2(efi_system_table_t *sys_table_arg)
  63 {
  64         efi_guid_t tcg2_guid = EFI_TCG2_PROTOCOL_GUID;
  65         efi_guid_t linux_eventlog_guid = LINUX_EFI_TPM_EVENT_LOG_GUID;
  66         efi_status_t status;
  67         efi_physical_addr_t log_location = 0, log_last_entry = 0;
  68         struct linux_efi_tpm_eventlog *log_tbl = NULL;
  69         unsigned long first_entry_addr, last_entry_addr;
  70         size_t log_size, last_entry_size;
  71         efi_bool_t truncated;
  72         void *tcg2_protocol = NULL;
  73
  74         status = efi_call_early(locate_protocol, &tcg2_guid, NULL,
  75                                 &tcg2_protocol);
  76         if (status != EFI_SUCCESS)
  77                 return;
  78
  79         status = efi_call_proto(efi_tcg2_protocol, get_event_log, tcg2_protocol,
  80                                 EFI_TCG2_EVENT_LOG_FORMAT_TCG_1_2,
  81                                 &log_location, &log_last_entry, &truncated);
  82         if (status != EFI_SUCCESS)
  83                 return;
  84
  85         if (!log_location)
  86                 return;
  87         first_entry_addr = (unsigned long) log_location;
  88
  89         /*
  90          * We populate the EFI table even if the logs are empty.
  91          */
  92         if (!log_last_entry) {
  93                 log_size = 0;
  94         } else {
  95                 last_entry_addr = (unsigned long) log_last_entry;
  96                 /*
  97                  * get_event_log only returns the address of the last entry.
  98                  * We need to calculate its size to deduce the full size of
  99                  * the logs.
 100                  */
 101                 last_entry_size = sizeof(struct tcpa_event) +
 102                         ((struct tcpa_event *) last_entry_addr)->event_size;
 103                 log_size = log_last_entry - log_location + last_entry_size;
 104         }
 105
 106         /* Allocate space for the logs and copy them. */
 107         status = efi_call_early(allocate_pool, EFI_LOADER_DATA,
 108                                 sizeof(*log_tbl) + log_size,
 109                                 (void **) &log_tbl);
 110
 111         if (status != EFI_SUCCESS) {
 112                 efi_printk(sys_table_arg,
 113                            "Unable to allocate memory for event log\n");
 114                 return;
 115         }
 116
 117         memset(log_tbl, 0, sizeof(*log_tbl) + log_size);
 118         log_tbl->size = log_size;
 119         log_tbl->version = EFI_TCG2_EVENT_LOG_FORMAT_TCG_1_2;
 120         memcpy(log_tbl->log, (void *) first_entry_addr, log_size);
 121
 122         status = efi_call_early(install_configuration_table,
 123                                 &linux_eventlog_guid, log_tbl);
 124         if (status != EFI_SUCCESS)
 125                 goto err_free;
 126         return;
 127
 128 err_free:
 129         efi_call_early(free_pool, log_tbl);
 130 }
 131
 132 void efi_retrieve_tpm2_eventlog(efi_system_table_t *sys_table_arg)
 133 {
 134         /* Only try to retrieve the logs in 1.2 format. */
 135         efi_retrieve_tpm2_eventlog_1_2(sys_table_arg);
 136 }