Re: Grub get and set efi variables

[Ignat Korchagin]

Actually, I submitted similar patch recently as well. It provides read
function for variables and accepts a hint on how to process them. The
original patch is here:
https://lists.gnu.org/archive/html/grub-devel/2015-09/msg00043.html.

Probably, I forgot to enable plain-text mode, so it got there as a
binary attachment. I will repeat it here for convenience.

diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def
index 9764cd2..49fa3ec 100644
--- a/grub-core/Makefile.core.def
+++ b/grub-core/Makefile.core.def
@@ -728,6 +728,12 @@ 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..ca206eb
--- /dev/null
+++ b/grub-core/commands/efi/efivar.c
@@ -0,0 +1,146 @@
+/* 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>
+
+GRUB_MOD_LICENSE ("GPLv3+");
+
+static const struct grub_arg_option options[] = {
+  {"type", 't', GRUB_ARG_OPTION_OPTIONAL, N_("Parse EFI_VAR as
specific type (hex, uint8, string). Default: hex."), N_("TYPE"),
ARG_TYPE_STRING},
+  {0, 0, 0, 0, 0, 0}
+};
+
+enum efi_var_type
+  {
+    EFI_VAR_STRING = 0,
+    EFI_VAR_UINT8,
+    EFI_VAR_HEX,
+    EFI_VAR_INVALID = -1
+  };
+
+static enum efi_var_type
+parse_efi_var_type (const char *type)
+{
+  if (!grub_strncmp (type, "string", sizeof("string")))
+    return EFI_VAR_STRING;
+
+  if (!grub_strncmp (type, "uint8", sizeof("uint8")))
+    return EFI_VAR_UINT8;
+
+  if (!grub_strncmp (type, "hex", sizeof("hex")))
+    return EFI_VAR_HEX;
+
+  return EFI_VAR_INVALID;
+}
+
+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;
+
+  if (2 != argc)
+    return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("two arguments 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 EFI variable type"));
+
+  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"));
+
+  switch (efi_type)
+  {
+    case EFI_VAR_STRING:
+      env_var = grub_malloc (efi_var_size + 1);
+      if (!env_var)
+        {
+          status = grub_error (GRUB_ERR_OUT_OF_MEMORY, N_("out of memory"));
+          break;
+        }
+      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"));
+          break;
+        }
+      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"));
+          break;
+        }
+      for (i = 0; i < efi_var_size; i++)
+        grub_snprintf (env_var + (i * 2), 3, "%02x", ((grub_uint8_t
*)efi_var)[i]);
+      break;
+
+    default:
+      status = grub_error (GRUB_ERR_BUG, N_("should not happen (bug
in module?)"));
+  }
+
+  status = grub_env_set (args[1], env_var);
+
+  if (env_var)
+    grub_free (env_var);
+
+  if (efi_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_("[-t TYPE] EFI_VAR ENV_VAR"),
+ N_("Read EFI variable and put its contents in environment
variable."), options);
+}
+
+GRUB_MOD_FINI (efivar)
+{
+  if (cmd)
+    grub_unregister_extcmd (cmd);
+}


On Thu, Nov 5, 2015 at 10:25 AM, SevenBits <address@hidden> wrote:
> On Wednesday, November 4, 2015, Andrei Borzenkov <address@hidden>
> wrote:
>>
>> 04.11.2015 02:05, Mat Troi пишет:
>>>
>>> Hi SevenBits,
>>>
>>> Thanks for letting me know.  Out of curiosity, any particular reason why
>>> this patch did not get merged?  It looks to be a useful feature.
>>>
>>
>> First, this patch was reverse patch :)
>
>
> Yeah, I think I had accidentally passed the arguments to the diff command in
> the wrong order.
>
>>
>>
>> I am not convinced making it easy to set EFI variable from within GRUB is
>> good thing, because there are known reports about systems rendered
>> unbootable by writing too much into EFI flash. What is your use case that
>> absolutely requires setting EFI variables? How are you going to implement it
>> on other platforms?
>
>
> I should probably note that I wrote this patch for a specific project of
> mine which required the ability to read UEFI variables. I added in write
> functionality for good measure because I could. But I agree, this would only
> encourage tinkering and users messing with their systems and potentially
> bricking it, which would of course be blamed on GRUB.
>
>>
>>
>> Reading does not harm and may be useful, but then it should provide
>> generic interface to access arbitrary vendor namespace, not only EFI global
>> variables, and handle arbitrary binary data, even if initial implementation
>> handles only subset of them. Once someone starts to use it changing it will
>> be much more difficult.
>>
>> Maybe it should take hints how to interpret variable values, or have
>> format option akin to printf.
>
>
> I would be happy to resume work on this, and debase it on the current code,
> if GRUB has a clear need for such functionality. I would prefer to have it
> be clear what the patch should consist of, though.
>
> A key question would be how to e.g. handle arbitrary data stored in
> variables if it is not something easily represent able like a string. Right
> now, the patch stores it's value into an environment variable specified by
> the user. Unless the powers that be think otherwise, I think this is the
> best way to go.
>
>>
>>
>>> Thanks,
>>> Mat
>>>
>>> On Tue, Nov 3, 2015 at 12:12 PM, SevenBits <address@hidden>
>>> wrote:
>>>
>>>> On Tuesday, November 3, 2015, Mat Troi <address@hidden> wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> Searching through google, I see there was an email thread to add a
>>>>> patch
>>>>> for getting and setting efi variable in GRUB2.
>>>>> https://lists.gnu.org/archive/html/grub-devel/2013-11/msg00328.html
>>>>>
>>>>> However, looking at the tree, it doesn't look like this patch was
>>>>> added,
>>>>> am I missing something?  Does anyone know if we have command to get/set
>>>>> efi
>>>>> variables in GRUB2?
>>>>>
>>>>>
>>>>>
>>>>> http://git.savannah.gnu.org/gitweb/?p=grub.git;a=tree;f=grub-core/commands/efi;h=005fd2efc9a2eede2a1eb1cab8081c360219107b;hb=HEAD
>>>>>
>>>>>
>>>> I'm the author of that patch. No, it was never merged into the tree. As
>>>> far as I know, there is no equivalent functionality; GRUB does not
>>>> support
>>>> this feature.
>>>>
>>>>
>>>>> Thanks,
>>>>> Mat
>>>>>
>>>>
>>>> _______________________________________________
>>>> Grub-devel mailing list
>>>> address@hidden
>>>> https://lists.gnu.org/mailman/listinfo/grub-devel
>>>>
>>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> Grub-devel mailing list
>>> address@hidden
>>> https://lists.gnu.org/mailman/listinfo/grub-devel
>>>
>>
>>
>> _______________________________________________
>> Grub-devel mailing list
>> address@hidden
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>
>
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