drivers/firmware/efi/libstub/random.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2016 Linaro Ltd;  <ard.biesheuvel@linaro.org>
   4  */
   5
   6 #include <linux/efi.h>
   7 #include <asm/efi.h>
   8
   9 #include "efistub.h"
  10
  11 typedef union efi_rng_protocol efi_rng_protocol_t;
  12
  13 union efi_rng_protocol {
  14         struct {
  15                 efi_status_t (__efiapi *get_info)(efi_rng_protocol_t *,
  16                                                   unsigned long *,
  17                                                   efi_guid_t *);
  18                 efi_status_t (__efiapi *get_rng)(efi_rng_protocol_t *,
  19                                                  efi_guid_t *, unsigned long,
  20                                                  u8 *out);
  21         };
  22         struct {
  23                 u32 get_info;
  24                 u32 get_rng;
  25         } mixed_mode;
  26 };
  27
  28 /**
  29  * efi_get_random_bytes() - fill a buffer with random bytes
  30  * @size:       size of the buffer
  31  * @out:        caller allocated buffer to receive the random bytes
  32  *
  33  * The call will fail if either the firmware does not implement the
  34  * EFI_RNG_PROTOCOL or there are not enough random bytes available to fill
  35  * the buffer.
  36  *
  37  * Return:      status code
  38  */
  39 efi_status_t efi_get_random_bytes(unsigned long size, u8 *out)
  40 {
  41         efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
  42         efi_status_t status;
  43         efi_rng_protocol_t *rng = NULL;
  44
  45         status = efi_bs_call(locate_protocol, &rng_proto, NULL, (void **)&rng);
  46         if (status != EFI_SUCCESS)
  47                 return status;
  48
  49         return efi_call_proto(rng, get_rng, NULL, size, out);
  50 }
  51
  52 /**
  53  * efi_random_get_seed() - provide random seed as configuration table
  54  *
  55  * The EFI_RNG_PROTOCOL is used to read random bytes. These random bytes are
  56  * saved as a configuration table which can be used as entropy by the kernel
  57  * for the initialization of its pseudo random number generator.
  58  *
  59  * If the EFI_RNG_PROTOCOL is not available or there are not enough random bytes
  60  * available, the configuration table will not be installed and an error code
  61  * will be returned.
  62  *
  63  * Return:      status code
  64  */
  65 efi_status_t efi_random_get_seed(void)
  66 {
  67         efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
  68         efi_guid_t rng_algo_raw = EFI_RNG_ALGORITHM_RAW;
  69         efi_guid_t rng_table_guid = LINUX_EFI_RANDOM_SEED_TABLE_GUID;
  70         efi_rng_protocol_t *rng = NULL;
  71         struct linux_efi_random_seed *seed = NULL;
  72         efi_status_t status;
  73
  74         status = efi_bs_call(locate_protocol, &rng_proto, NULL, (void **)&rng);
  75         if (status != EFI_SUCCESS)
  76                 return status;
  77
  78         status = efi_bs_call(allocate_pool, EFI_RUNTIME_SERVICES_DATA,
  79                              sizeof(*seed) + EFI_RANDOM_SEED_SIZE,
  80                              (void **)&seed);
  81         if (status != EFI_SUCCESS)
  82                 return status;
  83
  84         status = efi_call_proto(rng, get_rng, &rng_algo_raw,
  85                                  EFI_RANDOM_SEED_SIZE, seed->bits);
  86
  87         if (status == EFI_UNSUPPORTED)
  88                 /*
  89                  * Use whatever algorithm we have available if the raw algorithm
  90                  * is not implemented.
  91                  */
  92                 status = efi_call_proto(rng, get_rng, NULL,
  93                                         EFI_RANDOM_SEED_SIZE, seed->bits);
  94
  95         if (status != EFI_SUCCESS)
  96                 goto err_freepool;
  97
  98         seed->size = EFI_RANDOM_SEED_SIZE;
  99         status = efi_bs_call(install_configuration_table, &rng_table_guid, seed);
 100         if (status != EFI_SUCCESS)
 101                 goto err_freepool;
 102
 103         return EFI_SUCCESS;
 104
 105 err_freepool:
 106         efi_bs_call(free_pool, seed);
 107         return status;
 108 }