a4356538d0
Currently if an EFI firmware fails to do a TPM measurement for a file, the error will be propagated to the verifiers framework which will prevent it to be opened. This mean that buggy firmwares will lead to the system not booting because files won't be allowed to be loaded. But a failure to do a TPM measurement isn't expected to be a fatal error that causes the system to be unbootable. To avoid this, don't return errors from .write and .verify_string callbacks and just print a debug message in the case of a TPM measurement failure. Add an environment variable, tpm_fail_fatal, to restore the previous behavior. Also-authored-by: Javier Martinez Canillas <javierm@redhat.com> Signed-off-by: Javier Martinez Canillas <javierm@redhat.com> Signed-off-by: Robbie Harwood <rharwood@redhat.com> Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
113 lines
3.0 KiB
C
113 lines
3.0 KiB
C
/*
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* GRUB -- GRand Unified Bootloader
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* Copyright (C) 2018 Free Software Foundation, Inc.
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*
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* GRUB is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* GRUB is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with GRUB. If not, see <http://www.gnu.org/licenses/>.
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*
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* Core TPM support code.
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*/
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#include <grub/env.h>
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#include <grub/err.h>
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#include <grub/i18n.h>
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#include <grub/misc.h>
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#include <grub/mm.h>
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#include <grub/tpm.h>
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#include <grub/term.h>
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#include <grub/verify.h>
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#include <grub/dl.h>
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GRUB_MOD_LICENSE ("GPLv3+");
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static grub_err_t
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grub_tpm_verify_init (grub_file_t io,
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enum grub_file_type type __attribute__ ((unused)),
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void **context, enum grub_verify_flags *flags)
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{
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*context = io->name;
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*flags |= GRUB_VERIFY_FLAGS_SINGLE_CHUNK;
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return GRUB_ERR_NONE;
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}
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static inline bool
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is_tpm_fail_fatal (void)
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{
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return grub_env_get_bool ("tpm_fail_fatal", false);
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}
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static grub_err_t
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grub_tpm_verify_write (void *context, void *buf, grub_size_t size)
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{
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grub_err_t status = grub_tpm_measure (buf, size, GRUB_BINARY_PCR, context);
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if (status == GRUB_ERR_NONE)
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return GRUB_ERR_NONE;
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grub_dprintf ("tpm", "Measuring buffer failed: %d\n", status);
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return is_tpm_fail_fatal () ? status : GRUB_ERR_NONE;
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}
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static grub_err_t
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grub_tpm_verify_string (char *str, enum grub_verify_string_type type)
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{
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const char *prefix = NULL;
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char *description;
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grub_err_t status;
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switch (type)
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{
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case GRUB_VERIFY_KERNEL_CMDLINE:
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prefix = "kernel_cmdline: ";
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break;
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case GRUB_VERIFY_MODULE_CMDLINE:
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prefix = "module_cmdline: ";
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break;
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case GRUB_VERIFY_COMMAND:
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prefix = "grub_cmd: ";
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break;
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}
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description = grub_malloc (grub_strlen (str) + grub_strlen (prefix) + 1);
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if (!description)
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return grub_errno;
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grub_memcpy (description, prefix, grub_strlen (prefix));
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grub_memcpy (description + grub_strlen (prefix), str,
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grub_strlen (str) + 1);
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status =
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grub_tpm_measure ((unsigned char *) str, grub_strlen (str),
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GRUB_STRING_PCR, description);
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grub_free (description);
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if (status == GRUB_ERR_NONE)
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return GRUB_ERR_NONE;
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grub_dprintf ("tpm", "Measuring string %s failed: %d\n", str, status);
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return is_tpm_fail_fatal () ? status : GRUB_ERR_NONE;
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}
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struct grub_file_verifier grub_tpm_verifier = {
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.name = "tpm",
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.init = grub_tpm_verify_init,
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.write = grub_tpm_verify_write,
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.verify_string = grub_tpm_verify_string,
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};
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GRUB_MOD_INIT (tpm)
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{
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grub_verifier_register (&grub_tpm_verifier);
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}
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GRUB_MOD_FINI (tpm)
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{
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grub_verifier_unregister (&grub_tpm_verifier);
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}
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