security/integrity/platform_certs/load_uefi.c

   1 // SPDX-License-Identifier: GPL-2.0
   2
   3 #include <linux/kernel.h>
   4 #include <linux/sched.h>
   5 #include <linux/cred.h>
   6 #include <linux/err.h>
   7 #include <linux/efi.h>
   8 #include <linux/slab.h>
   9 #include <keys/asymmetric-type.h>
  10 #include <keys/system_keyring.h>
  11 #include "../integrity.h"
  12 #include "keyring_handler.h"
  13
  14 /*
  15  * Look to see if a UEFI variable called MokIgnoreDB exists and return true if
  16  * it does.
  17  *
  18  * This UEFI variable is set by the shim if a user tells the shim to not use
  19  * the certs/hashes in the UEFI db variable for verification purposes.  If it
  20  * is set, we should ignore the db variable also and the true return indicates
  21  * this.
  22  */
  23 static __init bool uefi_check_ignore_db(void)
  24 {
  25         efi_status_t status;
  26         unsigned int db = 0;
  27         unsigned long size = sizeof(db);
  28         efi_guid_t guid = EFI_SHIM_LOCK_GUID;
  29
  30         status = efi.get_variable(L"MokIgnoreDB", &guid, NULL, &size, &db);
  31         return status == EFI_SUCCESS;
  32 }
  33
  34 /*
  35  * Get a certificate list blob from the named EFI variable.
  36  */
  37 static __init void *get_cert_list(efi_char16_t *name, efi_guid_t *guid,
  38                                   unsigned long *size, efi_status_t *status)
  39 {
  40         unsigned long lsize = 4;
  41         unsigned long tmpdb[4];
  42         void *db;
  43
  44         *status = efi.get_variable(name, guid, NULL, &lsize, &tmpdb);
  45         if (*status == EFI_NOT_FOUND)
  46                 return NULL;
  47
  48         if (*status != EFI_BUFFER_TOO_SMALL) {
  49                 pr_err("Couldn't get size: 0x%lx\n", *status);
  50                 return NULL;
  51         }
  52
  53         db = kmalloc(lsize, GFP_KERNEL);
  54         if (!db)
  55                 return NULL;
  56
  57         *status = efi.get_variable(name, guid, NULL, &lsize, db);
  58         if (*status != EFI_SUCCESS) {
  59                 kfree(db);
  60                 pr_err("Error reading db var: 0x%lx\n", *status);
  61                 return NULL;
  62         }
  63
  64         *size = lsize;
  65         return db;
  66 }
  67
  68 /*
  69  * load_moklist_certs() - Load MokList certs
  70  *
  71  * Load the certs contained in the UEFI MokListRT database into the
  72  * platform trusted keyring.
  73  *
  74  * This routine checks the EFI MOK config table first. If and only if
  75  * that fails, this routine uses the MokListRT ordinary UEFI variable.
  76  *
  77  * Return:      Status
  78  */
  79 static int __init load_moklist_certs(void)
  80 {
  81         struct efi_mokvar_table_entry *mokvar_entry;
  82         efi_guid_t mok_var = EFI_SHIM_LOCK_GUID;
  83         void *mok;
  84         unsigned long moksize;
  85         efi_status_t status;
  86         int rc;
  87
  88         /* First try to load certs from the EFI MOKvar config table.
  89          * It's not an error if the MOKvar config table doesn't exist
  90          * or the MokListRT entry is not found in it.
  91          */
  92         mokvar_entry = efi_mokvar_entry_find("MokListRT");
  93         if (mokvar_entry) {
  94                 rc = parse_efi_signature_list("UEFI:MokListRT (MOKvar table)",
  95                                               mokvar_entry->data,
  96                                               mokvar_entry->data_size,
  97                                               get_handler_for_db);
  98                 /* All done if that worked. */
  99                 if (!rc)
 100                         return rc;
 101
 102                 pr_err("Couldn't parse MokListRT signatures from EFI MOKvar config table: %d\n",
 103                        rc);
 104         }
 105
 106         /* Get MokListRT. It might not exist, so it isn't an error
 107          * if we can't get it.
 108          */
 109         mok = get_cert_list(L"MokListRT", &mok_var, &moksize, &status);
 110         if (mok) {
 111                 rc = parse_efi_signature_list("UEFI:MokListRT",
 112                                               mok, moksize, get_handler_for_db);
 113                 kfree(mok);
 114                 if (rc)
 115                         pr_err("Couldn't parse MokListRT signatures: %d\n", rc);
 116                 return rc;
 117         }
 118         if (status == EFI_NOT_FOUND)
 119                 pr_debug("MokListRT variable wasn't found\n");
 120         else
 121                 pr_info("Couldn't get UEFI MokListRT\n");
 122         return 0;
 123 }
 124
 125 /*
 126  * load_uefi_certs() - Load certs from UEFI sources
 127  *
 128  * Load the certs contained in the UEFI databases into the platform trusted
 129  * keyring and the UEFI blacklisted X.509 cert SHA256 hashes into the blacklist
 130  * keyring.
 131  */
 132 static int __init load_uefi_certs(void)
 133 {
 134         efi_guid_t secure_var = EFI_IMAGE_SECURITY_DATABASE_GUID;
 135         void *db = NULL, *dbx = NULL;
 136         unsigned long dbsize = 0, dbxsize = 0;
 137         efi_status_t status;
 138         int rc = 0;
 139
 140         if (!efi_rt_services_supported(EFI_RT_SUPPORTED_GET_VARIABLE))
 141                 return false;
 142
 143         /* Get db and dbx.  They might not exist, so it isn't an error
 144          * if we can't get them.
 145          */
 146         if (!uefi_check_ignore_db()) {
 147                 db = get_cert_list(L"db", &secure_var, &dbsize, &status);
 148                 if (!db) {
 149                         if (status == EFI_NOT_FOUND)
 150                                 pr_debug("MODSIGN: db variable wasn't found\n");
 151                         else
 152                                 pr_err("MODSIGN: Couldn't get UEFI db list\n");
 153                 } else {
 154                         rc = parse_efi_signature_list("UEFI:db",
 155                                         db, dbsize, get_handler_for_db);
 156                         if (rc)
 157                                 pr_err("Couldn't parse db signatures: %d\n",
 158                                        rc);
 159                         kfree(db);
 160                 }
 161         }
 162
 163         dbx = get_cert_list(L"dbx", &secure_var, &dbxsize, &status);
 164         if (!dbx) {
 165                 if (status == EFI_NOT_FOUND)
 166                         pr_debug("dbx variable wasn't found\n");
 167                 else
 168                         pr_info("Couldn't get UEFI dbx list\n");
 169         } else {
 170                 rc = parse_efi_signature_list("UEFI:dbx",
 171                                               dbx, dbxsize,
 172                                               get_handler_for_dbx);
 173                 if (rc)
 174                         pr_err("Couldn't parse dbx signatures: %d\n", rc);
 175                 kfree(dbx);
 176         }
 177
 178         /* Load the MokListRT certs */
 179         rc = load_moklist_certs();
 180
 181         return rc;
 182 }
 183 late_initcall(load_uefi_certs);