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