Re: Grub get and set efi variables

[Andrei Borzenkov <arvidjaar@gmail.com>]

17.11.2015 14:48, Ignat Korchagin пишет:
> Please, see updated patch below. I tried to reuse GRUB hexdump
> function, so as a result dump will not work with setting vatiables -
> just dumping to stdout. But it doesn't make sense to assign dump to a
> variable anyway.
> 
> diff --git a/grub-core/commands/efi/efivar.c b/grub-core/commands/efi/efivar.c
> new file mode 100644
> index 0000000..3ffd5ca
> --- /dev/null
> +++ b/grub-core/commands/efi/efivar.c
> @@ -0,0 +1,253 @@
> +/* 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;
> +

Should not this be strcmp, not str*n*cmp?

> +  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_("two arguments expected"));

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"));
> +          break;
> +        }
> +
> +      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"));
> +          break;
> +        }
> +      grub_memcpy (env_var, efi_var, efi_var_size);
> +      env_var[efi_var_size] = '\0';

That would be wrong ("raw" implies no modification) but I am not keen on
keeping "raw" as was discussed.

> +      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;
> +
> +    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?)"));
> +  }
> +
> +  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:
> +
> +  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_("[-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);
> +}
> diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def
> index a6101de..2c8f023 100644
> --- a/grub-core/Makefile.core.def
> +++ b/grub-core/Makefile.core.def
> @@ -728,6 +728,12 @@
>  };
> 
>  module = {
> +  name = efivar;
> +  efi = commands/efi/efivar.c;
> +  enable = efi;
> +};
> +
> +module = {
>    name = blocklist;
>    common = commands/blocklist.c;
>  };
> 
> On Sat, Nov 14, 2015 at 4:03 AM, Andrei Borzenkov <arvidjaar@gmail.com> wrote:
>> 13.11.2015 22:42, Ignat Korchagin пишет:
>>>>>>
>>>>>> +static enum efi_var_type
>>>>>> +parse_efi_var_type (const char *type)
>>>>>> +{
>>>>>> +  if (!grub_strncmp (type, "string", sizeof("string")))
>>>>>> +    return EFI_VAR_STRING;
>>>>>> +
>>>>>
>>>>>
>>>>>
>>>>> I think this should be "ascii" or "utf8". "string" is too ambiguous in
>>>>> UEFI
>>>>> environment, it can also mean sequence of UCS-2 characters.
>>>>
>>>> I'm still not sure how exactly GRUB + UEFI interprets "raw buffers"
>>>> when printing. Maybe, to avoid confusion, it might be better to
>>>> completely remove this option. Basically, you do not want to interpret
>>>> raw buffers as strings. For best compatibility "hex" mode should be
>>>> promoted, I guess. What do you think?
>>>
>>> Checked again the UEFI spec. For globally defined variables which are
>>> strings they specify ASCII. So if we leave this option, ascii is the
>>> best name.
>>>
>>
>> What about
>>
>>   - ascii - print ASCII characters verbatim, escape non-ASCII in usual way
>> (similar to "od -c")
>>
>>   - raw - simply put raw variable without any interpretation.
>>
>> This is better aligned with argument describing output formatting rather
>> than attempting to "type" variable.
>>
>> Alternative (or in addition to) ascii - dump which prints usual pretty hex
>> dump of content (hexdump -C). This is handy to interactively look at
>> variable content.
>>
>> Or, and change name from --type to --format :)
>>
>>
>> _______________________________________________
>> Grub-devel mailing list
>> Grub-devel@gnu.org
>> https://lists.gnu.org/mailman/listinfo/grub-devel
> 
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