src/basic/efivars.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2
   3 #include <errno.h>
   4 #include <fcntl.h>
   5 #include <limits.h>
   6 #include <linux/fs.h>
   7 #include <stdio.h>
   8 #include <stdlib.h>
   9 #include <sys/stat.h>
  10 #include <unistd.h>
  11
  12 #include "sd-id128.h"
  13
  14 #include "alloc-util.h"
  15 #include "chattr-util.h"
  16 #include "efivars.h"
  17 #include "fd-util.h"
  18 #include "io-util.h"
  19 #include "macro.h"
  20 #include "stdio-util.h"
  21 #include "strv.h"
  22 #include "time-util.h"
  23 #include "utf8.h"
  24
  25 #if ENABLE_EFI
  26
  27 char* efi_variable_path(sd_id128_t vendor, const char *name) {
  28         char *p;
  29
  30         if (asprintf(&p,
  31                      "/sys/firmware/efi/efivars/%s-" SD_ID128_UUID_FORMAT_STR,
  32                      name, SD_ID128_FORMAT_VAL(vendor)) < 0)
  33                 return NULL;
  34
  35         return p;
  36 }
  37
  38 int efi_get_variable(
  39                 sd_id128_t vendor,
  40                 const char *name,
  41                 uint32_t *ret_attribute,
  42                 void **ret_value,
  43                 size_t *ret_size) {
  44
  45         _cleanup_close_ int fd = -1;
  46         _cleanup_free_ char *p = NULL;
  47         _cleanup_free_ void *buf = NULL;
  48         struct stat st;
  49         uint32_t a;
  50         ssize_t n;
  51
  52         assert(name);
  53
  54         p = efi_variable_path(vendor, name);
  55         if (!p)
  56                 return -ENOMEM;
  57
  58         if (!ret_value && !ret_size && !ret_attribute) {
  59                 /* If caller is not interested in anything, just check if the variable exists and is readable
  60                  * to us. */
  61                 if (access(p, R_OK) < 0)
  62                         return -errno;
  63
  64                 return 0;
  65         }
  66
  67         fd = open(p, O_RDONLY|O_NOCTTY|O_CLOEXEC);
  68         if (fd < 0)
  69                 return -errno;
  70
  71         if (fstat(fd, &st) < 0)
  72                 return -errno;
  73         if (st.st_size < 4)
  74                 return -ENODATA;
  75         if (st.st_size > 4*1024*1024 + 4)
  76                 return -E2BIG;
  77
  78         if (ret_value || ret_attribute) {
  79                 n = read(fd, &a, sizeof(a));
  80                 if (n < 0)
  81                         return -errno;
  82                 if (n != sizeof(a))
  83                         return -EIO;
  84         }
  85
  86         if (ret_value) {
  87                 buf = malloc(st.st_size - 4 + 2);
  88                 if (!buf)
  89                         return -ENOMEM;
  90
  91                 n = read(fd, buf, (size_t) st.st_size - 4);
  92                 if (n < 0)
  93                         return -errno;
  94                 if (n != st.st_size - 4)
  95                         return -EIO;
  96
  97                 /* Always NUL terminate (2 bytes, to protect UTF-16) */
  98                 ((char*) buf)[st.st_size - 4] = 0;
  99                 ((char*) buf)[st.st_size - 4 + 1] = 0;
 100         }
 101
 102         /* Note that efivarfs interestingly doesn't require ftruncate() to update an existing EFI variable
 103          * with a smaller value. */
 104
 105         if (ret_attribute)
 106                 *ret_attribute = a;
 107
 108         if (ret_value)
 109                 *ret_value = TAKE_PTR(buf);
 110
 111         if (ret_size)
 112                 *ret_size = (size_t) st.st_size - 4;
 113
 114         return 0;
 115 }
 116
 117 int efi_get_variable_string(sd_id128_t vendor, const char *name, char **p) {
 118         _cleanup_free_ void *s = NULL;
 119         size_t ss = 0;
 120         int r;
 121         char *x;
 122
 123         r = efi_get_variable(vendor, name, NULL, &s, &ss);
 124         if (r < 0)
 125                 return r;
 126
 127         x = utf16_to_utf8(s, ss);
 128         if (!x)
 129                 return -ENOMEM;
 130
 131         *p = x;
 132         return 0;
 133 }
 134
 135 int efi_set_variable(
 136                 sd_id128_t vendor,
 137                 const char *name,
 138                 const void *value,
 139                 size_t size) {
 140
 141         struct var {
 142                 uint32_t attr;
 143                 char buf[];
 144         } _packed_ * _cleanup_free_ buf = NULL;
 145         _cleanup_free_ char *p = NULL;
 146         _cleanup_close_ int fd = -1;
 147         bool saved_flags_valid = false;
 148         unsigned saved_flags;
 149         int r;
 150
 151         assert(name);
 152         assert(value || size == 0);
 153
 154         p = efi_variable_path(vendor, name);
 155         if (!p)
 156                 return -ENOMEM;
 157
 158         /* Newer efivarfs protects variables that are not in a whitelist with FS_IMMUTABLE_FL by default, to protect
 159          * them for accidental removal and modification. We are not changing these variables accidentally however,
 160          * hence let's unset the bit first. */
 161
 162         r = chattr_path(p, 0, FS_IMMUTABLE_FL, &saved_flags);
 163         if (r < 0 && r != -ENOENT)
 164                 log_debug_errno(r, "Failed to drop FS_IMMUTABLE_FL flag from '%s', ignoring: %m", p);
 165
 166         saved_flags_valid = r >= 0;
 167
 168         if (size == 0) {
 169                 if (unlink(p) < 0) {
 170                         r = -errno;
 171                         goto finish;
 172                 }
 173
 174                 return 0;
 175         }
 176
 177         fd = open(p, O_WRONLY|O_CREAT|O_NOCTTY|O_CLOEXEC, 0644);
 178         if (fd < 0) {
 179                 r = -errno;
 180                 goto finish;
 181         }
 182
 183         buf = malloc(sizeof(uint32_t) + size);
 184         if (!buf) {
 185                 r = -ENOMEM;
 186                 goto finish;
 187         }
 188
 189         buf->attr = EFI_VARIABLE_NON_VOLATILE|EFI_VARIABLE_BOOTSERVICE_ACCESS|EFI_VARIABLE_RUNTIME_ACCESS;
 190         memcpy(buf->buf, value, size);
 191
 192         r = loop_write(fd, buf, sizeof(uint32_t) + size, false);
 193         if (r < 0)
 194                 goto finish;
 195
 196         r = 0;
 197
 198 finish:
 199         if (saved_flags_valid) {
 200                 int q;
 201
 202                 /* Restore the original flags field, just in case */
 203                 if (fd < 0)
 204                         q = chattr_path(p, saved_flags, FS_IMMUTABLE_FL, NULL);
 205                 else
 206                         q = chattr_fd(fd, saved_flags, FS_IMMUTABLE_FL, NULL);
 207                 if (q < 0)
 208                         log_debug_errno(q, "Failed to restore FS_IMMUTABLE_FL on '%s', ignoring: %m", p);
 209         }
 210
 211         return r;
 212 }
 213
 214 int efi_set_variable_string(sd_id128_t vendor, const char *name, const char *v) {
 215         _cleanup_free_ char16_t *u16 = NULL;
 216
 217         u16 = utf8_to_utf16(v, strlen(v));
 218         if (!u16)
 219                 return -ENOMEM;
 220
 221         return efi_set_variable(vendor, name, u16, (char16_strlen(u16) + 1) * sizeof(char16_t));
 222 }
 223
 224 int efi_systemd_options_variable(char **line) {
 225         const char *e;
 226         int r;
 227
 228         assert(line);
 229
 230         /* For testing purposes it is sometimes useful to be able to override this */
 231         e = secure_getenv("SYSTEMD_EFI_OPTIONS");
 232         if (e) {
 233                 char *m;
 234
 235                 m = strdup(e);
 236                 if (!m)
 237                         return -ENOMEM;
 238
 239                 *line = m;
 240                 return 0;
 241         }
 242
 243         r = efi_get_variable_string(EFI_VENDOR_SYSTEMD, "SystemdOptions", line);
 244         if (r == -ENOENT)
 245                 return -ENODATA;
 246
 247         return r;
 248 }
 249 #endif