1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
|
From 6fe755c5c07bb386fda58306bfd19e4a1c974c53 Mon Sep 17 00:00:00 2001
From: Julian Andres Klode <julian.klode@canonical.com>
Date: Thu, 2 Dec 2021 15:03:53 +0100
Subject: kern/efi/sb: Reject non-kernel files in the shim_lock verifier
Upstream-Status: Backport [https://git.savannah.gnu.org/cgit/grub.git/commit/?id=6fe755c5c07bb386fda58306bfd19e4a1c974c53]
CVE: CVE-2022-28735
Signed-off-by: Hitendra Prajapati <hprajapati@mvista.com>
We must not allow other verifiers to pass things like the GRUB modules.
Instead of maintaining a blocklist, maintain an allowlist of things
that we do not care about.
This allowlist really should be made reusable, and shared by the
lockdown verifier, but this is the minimal patch addressing
security concerns where the TPM verifier was able to mark modules
as verified (or the OpenPGP verifier for that matter), when it
should not do so on shim-powered secure boot systems.
Fixes: CVE-2022-28735
Signed-off-by: Julian Andres Klode <julian.klode@canonical.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
grub-core/kern/efi/sb.c | 221 ++++++++++++++++++++++++++++++++++++++++
include/grub/verify.h | 1 +
2 files changed, 222 insertions(+)
create mode 100644 grub-core/kern/efi/sb.c
diff --git a/grub-core/kern/efi/sb.c b/grub-core/kern/efi/sb.c
new file mode 100644
index 0000000..89c4bb3
--- /dev/null
+++ b/grub-core/kern/efi/sb.c
@@ -0,0 +1,221 @@
+/*
+ * GRUB -- GRand Unified Bootloader
+ * Copyright (C) 2020 Free Software Foundation, 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/>.
+ *
+ * UEFI Secure Boot related checkings.
+ */
+
+#include <grub/efi/efi.h>
+#include <grub/efi/pe32.h>
+#include <grub/efi/sb.h>
+#include <grub/env.h>
+#include <grub/err.h>
+#include <grub/file.h>
+#include <grub/i386/linux.h>
+#include <grub/kernel.h>
+#include <grub/mm.h>
+#include <grub/types.h>
+#include <grub/verify.h>
+
+static grub_efi_guid_t shim_lock_guid = GRUB_EFI_SHIM_LOCK_GUID;
+
+/*
+ * Determine whether we're in secure boot mode.
+ *
+ * Please keep the logic in sync with the Linux kernel,
+ * drivers/firmware/efi/libstub/secureboot.c:efi_get_secureboot().
+ */
+grub_uint8_t
+grub_efi_get_secureboot (void)
+{
+ static grub_efi_guid_t efi_variable_guid = GRUB_EFI_GLOBAL_VARIABLE_GUID;
+ grub_efi_status_t status;
+ grub_efi_uint32_t attr = 0;
+ grub_size_t size = 0;
+ grub_uint8_t *secboot = NULL;
+ grub_uint8_t *setupmode = NULL;
+ grub_uint8_t *moksbstate = NULL;
+ grub_uint8_t secureboot = GRUB_EFI_SECUREBOOT_MODE_UNKNOWN;
+ const char *secureboot_str = "UNKNOWN";
+
+ status = grub_efi_get_variable ("SecureBoot", &efi_variable_guid,
+ &size, (void **) &secboot);
+
+ if (status == GRUB_EFI_NOT_FOUND)
+ {
+ secureboot = GRUB_EFI_SECUREBOOT_MODE_DISABLED;
+ goto out;
+ }
+
+ if (status != GRUB_EFI_SUCCESS)
+ goto out;
+
+ status = grub_efi_get_variable ("SetupMode", &efi_variable_guid,
+ &size, (void **) &setupmode);
+
+ if (status != GRUB_EFI_SUCCESS)
+ goto out;
+
+ if ((*secboot == 0) || (*setupmode == 1))
+ {
+ secureboot = GRUB_EFI_SECUREBOOT_MODE_DISABLED;
+ goto out;
+ }
+
+ /*
+ * See if a user has put the shim into insecure mode. If so, and if the
+ * variable doesn't have the runtime attribute set, we might as well
+ * honor that.
+ */
+ status = grub_efi_get_variable_with_attributes ("MokSBState", &shim_lock_guid,
+ &size, (void **) &moksbstate, &attr);
+
+ /* If it fails, we don't care why. Default to secure. */
+ if (status != GRUB_EFI_SUCCESS)
+ {
+ secureboot = GRUB_EFI_SECUREBOOT_MODE_ENABLED;
+ goto out;
+ }
+
+ if (!(attr & GRUB_EFI_VARIABLE_RUNTIME_ACCESS) && *moksbstate == 1)
+ {
+ secureboot = GRUB_EFI_SECUREBOOT_MODE_DISABLED;
+ goto out;
+ }
+
+ secureboot = GRUB_EFI_SECUREBOOT_MODE_ENABLED;
+
+ out:
+ grub_free (moksbstate);
+ grub_free (setupmode);
+ grub_free (secboot);
+
+ if (secureboot == GRUB_EFI_SECUREBOOT_MODE_DISABLED)
+ secureboot_str = "Disabled";
+ else if (secureboot == GRUB_EFI_SECUREBOOT_MODE_ENABLED)
+ secureboot_str = "Enabled";
+
+ grub_dprintf ("efi", "UEFI Secure Boot state: %s\n", secureboot_str);
+
+ return secureboot;
+}
+
+static grub_err_t
+shim_lock_verifier_init (grub_file_t io __attribute__ ((unused)),
+ enum grub_file_type type,
+ void **context __attribute__ ((unused)),
+ enum grub_verify_flags *flags)
+{
+ *flags = GRUB_VERIFY_FLAGS_NONE;
+
+ switch (type & GRUB_FILE_TYPE_MASK)
+ {
+ /* Files we check. */
+ case GRUB_FILE_TYPE_LINUX_KERNEL:
+ case GRUB_FILE_TYPE_MULTIBOOT_KERNEL:
+ case GRUB_FILE_TYPE_BSD_KERNEL:
+ case GRUB_FILE_TYPE_XNU_KERNEL:
+ case GRUB_FILE_TYPE_PLAN9_KERNEL:
+ case GRUB_FILE_TYPE_EFI_CHAINLOADED_IMAGE:
+ *flags = GRUB_VERIFY_FLAGS_SINGLE_CHUNK;
+ return GRUB_ERR_NONE;
+
+ /* Files that do not affect secureboot state. */
+ case GRUB_FILE_TYPE_NONE:
+ case GRUB_FILE_TYPE_LOOPBACK:
+ case GRUB_FILE_TYPE_LINUX_INITRD:
+ case GRUB_FILE_TYPE_OPENBSD_RAMDISK:
+ case GRUB_FILE_TYPE_XNU_RAMDISK:
+ case GRUB_FILE_TYPE_SIGNATURE:
+ case GRUB_FILE_TYPE_PUBLIC_KEY:
+ case GRUB_FILE_TYPE_PUBLIC_KEY_TRUST:
+ case GRUB_FILE_TYPE_PRINT_BLOCKLIST:
+ case GRUB_FILE_TYPE_TESTLOAD:
+ case GRUB_FILE_TYPE_GET_SIZE:
+ case GRUB_FILE_TYPE_FONT:
+ case GRUB_FILE_TYPE_ZFS_ENCRYPTION_KEY:
+ case GRUB_FILE_TYPE_CAT:
+ case GRUB_FILE_TYPE_HEXCAT:
+ case GRUB_FILE_TYPE_CMP:
+ case GRUB_FILE_TYPE_HASHLIST:
+ case GRUB_FILE_TYPE_TO_HASH:
+ case GRUB_FILE_TYPE_KEYBOARD_LAYOUT:
+ case GRUB_FILE_TYPE_PIXMAP:
+ case GRUB_FILE_TYPE_GRUB_MODULE_LIST:
+ case GRUB_FILE_TYPE_CONFIG:
+ case GRUB_FILE_TYPE_THEME:
+ case GRUB_FILE_TYPE_GETTEXT_CATALOG:
+ case GRUB_FILE_TYPE_FS_SEARCH:
+ case GRUB_FILE_TYPE_LOADENV:
+ case GRUB_FILE_TYPE_SAVEENV:
+ case GRUB_FILE_TYPE_VERIFY_SIGNATURE:
+ *flags = GRUB_VERIFY_FLAGS_SKIP_VERIFICATION;
+ return GRUB_ERR_NONE;
+
+ /* Other files. */
+ default:
+ return grub_error (GRUB_ERR_ACCESS_DENIED, N_("prohibited by secure boot policy"));
+ }
+}
+
+static grub_err_t
+shim_lock_verifier_write (void *context __attribute__ ((unused)), void *buf, grub_size_t size)
+{
+ grub_efi_shim_lock_protocol_t *sl = grub_efi_locate_protocol (&shim_lock_guid, 0);
+
+ if (!sl)
+ return grub_error (GRUB_ERR_ACCESS_DENIED, N_("shim_lock protocol not found"));
+
+ if (sl->verify (buf, size) != GRUB_EFI_SUCCESS)
+ return grub_error (GRUB_ERR_BAD_SIGNATURE, N_("bad shim signature"));
+
+ return GRUB_ERR_NONE;
+}
+
+struct grub_file_verifier shim_lock_verifier =
+ {
+ .name = "shim_lock_verifier",
+ .init = shim_lock_verifier_init,
+ .write = shim_lock_verifier_write
+ };
+
+void
+grub_shim_lock_verifier_setup (void)
+{
+ struct grub_module_header *header;
+ grub_efi_shim_lock_protocol_t *sl =
+ grub_efi_locate_protocol (&shim_lock_guid, 0);
+
+ /* shim_lock is missing, check if GRUB image is built with --disable-shim-lock. */
+ if (!sl)
+ {
+ FOR_MODULES (header)
+ {
+ if (header->type == OBJ_TYPE_DISABLE_SHIM_LOCK)
+ return;
+ }
+ }
+
+ /* Secure Boot is off. Do not load shim_lock. */
+ if (grub_efi_get_secureboot () != GRUB_EFI_SECUREBOOT_MODE_ENABLED)
+ return;
+
+ /* Enforce shim_lock_verifier. */
+ grub_verifier_register (&shim_lock_verifier);
+
+ grub_env_set ("shim_lock", "y");
+ grub_env_export ("shim_lock");
+}
diff --git a/include/grub/verify.h b/include/grub/verify.h
index cd129c3..672ae16 100644
--- a/include/grub/verify.h
+++ b/include/grub/verify.h
@@ -24,6 +24,7 @@
enum grub_verify_flags
{
+ GRUB_VERIFY_FLAGS_NONE = 0,
GRUB_VERIFY_FLAGS_SKIP_VERIFICATION = 1,
GRUB_VERIFY_FLAGS_SINGLE_CHUNK = 2,
/* Defer verification to another authority. */
--
2.25.1
|
