Re: Grub get and set efi variables

[Ignat Korchagin]

> Assuming uint8 remains - should not you check that variable size is exactly 1 
> byte in this case?
There are reports of a buggy firmware returning 4 bytes size for uint8
variables, however did not encounter them myself.

> Do we really need unit8 at all? "hex" already provides exactly the same 
> functionality, not? Do you think there are cases when uint8 is really 
> required?
Well, when checking for SecureBoot variable in grub configuration file
hex mode makes it look weird and creates a point of confusion. For
example to check if SecureBoot (suppose the result of the our command
is stored in secure_boot env variable in hex mode) is enabled one
should write:
if [ secure_boot = "01" ]
...
uint8 just allows to do a more straightforward config
if [ secure_boot = 1] - this case would be false for hex mode -
possible security breach
...

Added goto err in the module as pointed, see patch below. I will do a
follow-up patch for documentation once we get this confirmed.

diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def
index 0cc40bb..aa7b927 100644
--- a/grub-core/Makefile.core.def
+++ b/grub-core/Makefile.core.def
@@ -735,6 +735,12 @@ module = {
 };

 module = {
+  name = efivar;
+  efi = commands/efi/efivar.c;
+  enable = efi;
+};
+
+module = {
   name = blocklist;
   common = commands/blocklist.c;
 };
diff --git a/grub-core/commands/efi/efivar.c b/grub-core/commands/efi/efivar.c
new file mode 100644
index 0000000..7f5a957
--- /dev/null
+++ b/grub-core/commands/efi/efivar.c
@@ -0,0 +1,251 @@
+/* efivar.c - Read EFI global variables. */
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2015 Free Software Foundation, Inc.
+ *  Copyright (C) 2015 CloudFlare, Inc.
+ *
+ *  GRUB is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  GRUB is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <grub/types.h>
+#include <grub/mm.h>
+#include <grub/misc.h>
+#include <grub/efi/api.h>
+#include <grub/efi/efi.h>
+#include <grub/extcmd.h>
+#include <grub/env.h>
+#include <grub/lib/hexdump.h>
+
+GRUB_MOD_LICENSE ("GPLv3+");
+
+static const struct grub_arg_option options[] = {
+  {"format", 'f', GRUB_ARG_OPTION_OPTIONAL, N_("Parse EFI_VAR in
specific format (hex, uint8, ascii, raw, dump). Default: hex."),
N_("FORMAT"), ARG_TYPE_STRING},
+  {"set", 's', GRUB_ARG_OPTION_OPTIONAL, N_("Save parsed result to
environment variable (does not work with dump)."), N_("ENV_VAR"),
ARG_TYPE_STRING},
+  {0, 0, 0, 0, 0, 0}
+};
+
+enum efi_var_type
+  {
+    EFI_VAR_ASCII = 0,
+    EFI_VAR_RAW,
+    EFI_VAR_UINT8,
+    EFI_VAR_HEX,
+    EFI_VAR_DUMP,
+    EFI_VAR_INVALID = -1
+  };
+
+static enum efi_var_type
+parse_efi_var_type (const char *type)
+{
+  if (!grub_strncmp (type, "ascii", sizeof("ascii")))
+    return EFI_VAR_ASCII;
+
+  if (!grub_strncmp (type, "raw", sizeof("raw")))
+    return EFI_VAR_ASCII;
+
+  if (!grub_strncmp (type, "uint8", sizeof("uint8")))
+    return EFI_VAR_UINT8;
+
+  if (!grub_strncmp (type, "hex", sizeof("hex")))
+    return EFI_VAR_HEX;
+
+  if (!grub_strncmp (type, "dump", sizeof("dump")))
+    return EFI_VAR_DUMP;
+
+  return EFI_VAR_INVALID;
+}
+
+static int
+grub_print_ascii (char *str, char c)
+{
+  if (grub_iscntrl (c))
+  {
+    switch (c)
+      {
+        case '\0':
+          str[0] = '\\';
+          str[1] = '0';
+          return 2;
+
+        case '\a':
+          str[0] = '\\';
+          str[1] = 'a';
+          return 2;
+
+        case '\b':
+          str[0] = '\\';
+          str[1] = 'b';
+          return 2;
+
+        case '\f':
+          str[0] = '\\';
+          str[1] = 'f';
+          return 2;
+
+        case '\n':
+          str[0] = '\\';
+          str[1] = 'n';
+          return 2;
+
+        case '\r':
+          str[0] = '\\';
+          str[1] = 'r';
+          return 2;
+
+        case '\t':
+          str[0] = '\\';
+          str[1] = 't';
+          return 2;
+
+        case '\v':
+          str[0] = '\\';
+          str[1] = 'v';
+          return 2;
+
+        default:
+          str[0] = '.'; /* as in hexdump -C */
+          return 1;
+      }
+  }
+
+  str[0] = c;
+  return 1;
+}
+
+static grub_err_t
+grub_cmd_get_efi_var (struct grub_extcmd_context *ctxt,
+  int argc, char **args)
+{
+  struct grub_arg_list *state = ctxt->state;
+  grub_err_t status;
+  void *efi_var = NULL;
+  grub_size_t efi_var_size = 0;
+  enum efi_var_type efi_type = EFI_VAR_HEX;
+  grub_efi_guid_t global = GRUB_EFI_GLOBAL_VARIABLE_GUID;
+  char *env_var = NULL;
+  grub_size_t i;
+  char *ptr;
+
+  if (1 != argc)
+    return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("one argument expected"));
+
+  if (state[0].set)
+    efi_type = parse_efi_var_type (state[0].arg);
+
+  if (EFI_VAR_INVALID == efi_type)
+    return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("invalid format specifier"));
+
+  efi_var = grub_efi_get_variable (args[0], &global, &efi_var_size);
+  if (!efi_var || !efi_var_size)
+    {
+      status = grub_error (GRUB_ERR_READ_ERROR, N_("cannot read variable"));
+      goto err;
+    }
+
+  switch (efi_type)
+  {
+    case EFI_VAR_ASCII:
+      env_var = grub_malloc (efi_var_size * 2 + 1);
+      if (!env_var)
+        {
+          status = grub_error (GRUB_ERR_OUT_OF_MEMORY, N_("out of memory"));
+          goto err;
+        }
+
+      ptr = env_var;
+
+      for (i = 0; i < efi_var_size; i++)
+        ptr += grub_print_ascii (ptr, ((const char *)efi_var)[i]);
+      *ptr = '\0';
+      break;
+
+    case EFI_VAR_RAW:
+      env_var = grub_malloc (efi_var_size + 1);
+      if (!env_var)
+        {
+          status = grub_error (GRUB_ERR_OUT_OF_MEMORY, N_("out of memory"));
+          goto err;
+        }
+      grub_memcpy (env_var, efi_var, efi_var_size);
+      env_var[efi_var_size] = '\0';
+      break;
+
+    case EFI_VAR_UINT8:
+      env_var = grub_malloc (4);
+      if (!env_var)
+        {
+          status = grub_error (GRUB_ERR_OUT_OF_MEMORY, N_("out of memory"));
+          goto err;
+        }
+      grub_snprintf (env_var, 4, "%u", *((grub_uint8_t *)efi_var));
+      break;
+
+    case EFI_VAR_HEX:
+      env_var = grub_malloc (efi_var_size * 2 + 1);
+      if (!env_var)
+        {
+          status = grub_error (GRUB_ERR_OUT_OF_MEMORY, N_("out of memory"));
+          goto err;
+        }
+      for (i = 0; i < efi_var_size; i++)
+        grub_snprintf (env_var + (i * 2), 3, "%02x", ((grub_uint8_t
*)efi_var)[i]);
+      break;
+
+    case EFI_VAR_DUMP:
+      if (state[1].set)
+        status = grub_error (GRUB_ERR_BAD_ARGUMENT, N_("cannot set
variable with dump format specifier"));
+      else
+        {
+          hexdump (0, (char *)efi_var, efi_var_size);
+          status = GRUB_ERR_NONE;
+        }
+      break;
+
+    default:
+      status = grub_error (GRUB_ERR_BUG, N_("should not happen (bug
in module?)"));
+      goto err;
+  }
+
+  if (efi_type != EFI_VAR_DUMP)
+    {
+      if (state[1].set)
+        status = grub_env_set (state[1].arg, env_var);
+      else
+        {
+          grub_printf ("%s\n", (const char *)env_var);
+          status = GRUB_ERR_NONE;
+        }
+    }
+
+err:
+
+  grub_free (env_var);
+  grub_free (efi_var);
+
+  return status;
+}
+
+static grub_extcmd_t cmd = NULL;
+
+GRUB_MOD_INIT (efivar)
+{
+  cmd = grub_register_extcmd ("get_efivar", grub_cmd_get_efi_var, 0,
N_("[-f FORMAT] [-s ENV_VAR] EFI_VAR"),
+ N_("Read EFI variable and print it or save its contents to
environment variable."), options);
+}
+
+GRUB_MOD_FINI (efivar)
+{
+  if (cmd)
+    grub_unregister_extcmd (cmd);
+}