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- From 968de8c23c1cba0f18230f778ebcf6c412ec8ec5 Mon Sep 17 00:00:00 2001
- From: Dimitri John Ledkov <xnox@ubuntu.com>
- Date: Sat, 20 Feb 2021 17:10:34 +0000
- Subject: [PATCH] shim_lock: Only skip loading shim_lock verifier with explicit
- consent
- Commit 32ddc42c (efi: Only register shim_lock verifier if shim_lock
- protocol is found and SB enabled) reintroduced CVE-2020-15705 which
- previously only existed in the out-of-tree linuxefi patches and was
- fixed as part of the BootHole patch series.
- Under Secure Boot enforce loading shim_lock verifier. Allow skipping
- shim_lock verifier if SecureBoot/MokSBState EFI variables indicate
- skipping validations, or if GRUB image is built with --disable-shim-lock.
- Fixes: 132ddc42c (efi: Only register shim_lock verifier if shim_lock
- protocol is found and SB enabled)
- Fixes: CVE-2020-15705
- Fixes: CVE-2021-3418
- Reported-by: Dimitri John Ledkov <xnox@ubuntu.com>
- Signed-off-by: Dimitri John Ledkov <xnox@ubuntu.com>
- Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
- Signed-off-by: Stefan Sørensen <stefan.sorensen@spectralink.com>
- ---
- docs/grub.texi | 5 ++++-
- grub-core/kern/efi/sb.c | 17 ++++++++++++++++-
- include/grub/kernel.h | 3 ++-
- include/grub/util/install.h | 7 +++++--
- util/grub-install-common.c | 12 +++++++++---
- util/grub-mkimage.c | 8 +++++++-
- util/mkimage.c | 15 ++++++++++++++-
- 7 files changed, 57 insertions(+), 10 deletions(-)
- diff --git a/docs/grub.texi b/docs/grub.texi
- index bff6dfc..e302797 100644
- --- a/docs/grub.texi
- +++ b/docs/grub.texi
- @@ -5787,7 +5787,10 @@ secure boot chain.
- The GRUB, except the @command{chainloader} command, works with the UEFI secure
- boot and the shim. This functionality is provided by the shim_lock verifier. It
- is built into the @file{core.img} and is registered if the UEFI secure boot is
- -enabled.
- +enabled. The @samp{shim_lock} variable is set to @samp{y} when shim_lock verifier
- +is registered. If it is desired to use UEFI secure boot without shim, one can
- +disable shim_lock by disabling shim verification with MokSbState UEFI variable
- +or by building grub image with @samp{--disable-shim-lock} option.
-
- All GRUB modules not stored in the @file{core.img}, OS kernels, ACPI tables,
- Device Trees, etc. have to be signed, e.g, using PGP. Additionally, the commands
- diff --git a/grub-core/kern/efi/sb.c b/grub-core/kern/efi/sb.c
- index 5d7210a..41dadcd 100644
- --- a/grub-core/kern/efi/sb.c
- +++ b/grub-core/kern/efi/sb.c
- @@ -21,9 +21,11 @@
- #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>
- @@ -160,14 +162,27 @@ struct grub_file_verifier shim_lock_verifier =
- 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)
- - return;
- + {
- + 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/kernel.h b/include/grub/kernel.h
- index 133a37c..abbca5e 100644
- --- a/include/grub/kernel.h
- +++ b/include/grub/kernel.h
- @@ -29,7 +29,8 @@ enum
- OBJ_TYPE_CONFIG,
- OBJ_TYPE_PREFIX,
- OBJ_TYPE_PUBKEY,
- - OBJ_TYPE_DTB
- + OBJ_TYPE_DTB,
- + OBJ_TYPE_DISABLE_SHIM_LOCK
- };
-
- /* The module header. */
- diff --git a/include/grub/util/install.h b/include/grub/util/install.h
- index 8cb5056..11a8df8 100644
- --- a/include/grub/util/install.h
- +++ b/include/grub/util/install.h
- @@ -65,6 +65,8 @@
- N_("embed FILE as public key for signature checking"), 0}, \
- { "sbat", GRUB_INSTALL_OPTIONS_SBAT, N_("FILE"), 0, \
- N_("SBAT metadata"), 0 }, \
- + { "disable-shim-lock", GRUB_INSTALL_OPTIONS_DISABLE_SHIM_LOCK, 0, 0, \
- + N_("disable shim_lock verifier"), 0 }, \
- { "verbose", 'v', 0, 0, \
- N_("print verbose messages."), 1 }
-
- @@ -125,7 +127,8 @@ enum grub_install_options {
- GRUB_INSTALL_OPTIONS_GRUB_MKIMAGE,
- GRUB_INSTALL_OPTIONS_INSTALL_CORE_COMPRESS,
- GRUB_INSTALL_OPTIONS_DTB,
- - GRUB_INSTALL_OPTIONS_SBAT
- + GRUB_INSTALL_OPTIONS_SBAT,
- + GRUB_INSTALL_OPTIONS_DISABLE_SHIM_LOCK
- };
-
- extern char *grub_install_source_directory;
- @@ -187,7 +190,7 @@ grub_install_generate_image (const char *dir, const char *prefix,
- const struct grub_install_image_target_desc *image_target,
- int note,
- grub_compression_t comp, const char *dtb_file,
- - const char *sbat_path);
- + const char *sbat_path, const int disable_shim_lock);
-
- const struct grub_install_image_target_desc *
- grub_install_get_image_target (const char *arg);
- diff --git a/util/grub-install-common.c b/util/grub-install-common.c
- index 1fcccd2..13d9fe9 100644
- --- a/util/grub-install-common.c
- +++ b/util/grub-install-common.c
- @@ -308,6 +308,7 @@ handle_install_list (struct install_list *il, const char *val,
- static char **pubkeys;
- static size_t npubkeys;
- static char *sbat;
- +static int disable_shim_lock;
- static grub_compression_t compression;
-
- int
- @@ -344,6 +345,9 @@ grub_install_parse (int key, char *arg)
-
- sbat = xstrdup (arg);
- return 1;
- + case GRUB_INSTALL_OPTIONS_DISABLE_SHIM_LOCK:
- + disable_shim_lock = 1;
- + return 1;
-
- case GRUB_INSTALL_OPTIONS_VERBOSITY:
- verbosity++;
- @@ -506,10 +510,11 @@ grub_install_make_image_wrap_file (const char *dir, const char *prefix,
- " --output '%s' "
- " --dtb '%s' "
- "--sbat '%s' "
- - "--format '%s' --compression '%s' %s %s\n",
- + "--format '%s' --compression '%s' %s %s %s\n",
- dir, prefix,
- outname, dtb ? : "", sbat ? : "", mkimage_target,
- - compnames[compression], note ? "--note" : "", s);
- + compnames[compression], note ? "--note" : "",
- + disable_shim_lock ? "--disable-shim-lock" : "", s);
- free (s);
-
- tgt = grub_install_get_image_target (mkimage_target);
- @@ -519,7 +524,8 @@ grub_install_make_image_wrap_file (const char *dir, const char *prefix,
- grub_install_generate_image (dir, prefix, fp, outname,
- modules.entries, memdisk_path,
- pubkeys, npubkeys, config_path, tgt,
- - note, compression, dtb, sbat);
- + note, compression, dtb, sbat,
- + disable_shim_lock);
- while (dc--)
- grub_install_pop_module ();
- }
- diff --git a/util/grub-mkimage.c b/util/grub-mkimage.c
- index 75b8847..c0d5599 100644
- --- a/util/grub-mkimage.c
- +++ b/util/grub-mkimage.c
- @@ -82,6 +82,7 @@ static struct argp_option options[] = {
- {"format", 'O', N_("FORMAT"), 0, 0, 0},
- {"compression", 'C', "(xz|none|auto)", 0, N_("choose the compression to use for core image"), 0},
- {"sbat", 's', N_("FILE"), 0, N_("SBAT metadata"), 0},
- + {"disable-shim-lock", GRUB_INSTALL_OPTIONS_DISABLE_SHIM_LOCK, 0, 0, N_("disable shim_lock verifier"), 0},
- {"verbose", 'v', 0, 0, N_("print verbose messages."), 0},
- { 0, 0, 0, 0, 0, 0 }
- };
- @@ -126,6 +127,7 @@ struct arguments
- char *config;
- char *sbat;
- int note;
- + int disable_shim_lock;
- const struct grub_install_image_target_desc *image_target;
- grub_compression_t comp;
- };
- @@ -233,6 +235,10 @@ argp_parser (int key, char *arg, struct argp_state *state)
- arguments->sbat = xstrdup (arg);
- break;
-
- + case GRUB_INSTALL_OPTIONS_DISABLE_SHIM_LOCK:
- + arguments->disable_shim_lock = 1;
- + break;
- +
- case 'v':
- verbosity++;
- break;
- @@ -319,7 +325,7 @@ main (int argc, char *argv[])
- arguments.npubkeys, arguments.config,
- arguments.image_target, arguments.note,
- arguments.comp, arguments.dtb,
- - arguments.sbat);
- + arguments.sbat, arguments.disable_shim_lock);
-
- if (grub_util_file_sync (fp) < 0)
- grub_util_error (_("cannot sync `%s': %s"), arguments.output ? : "stdout",
- diff --git a/util/mkimage.c b/util/mkimage.c
- index b354ec1..a26cf76 100644
- --- a/util/mkimage.c
- +++ b/util/mkimage.c
- @@ -870,7 +870,7 @@ grub_install_generate_image (const char *dir, const char *prefix,
- size_t npubkeys, char *config_path,
- const struct grub_install_image_target_desc *image_target,
- int note, grub_compression_t comp, const char *dtb_path,
- - const char *sbat_path)
- + const char *sbat_path, int disable_shim_lock)
- {
- char *kernel_img, *core_img;
- size_t total_module_size, core_size;
- @@ -929,6 +929,9 @@ grub_install_generate_image (const char *dir, const char *prefix,
- if (sbat_path != NULL && image_target->id != IMAGE_EFI)
- grub_util_error (_(".sbat section can be embedded into EFI images only"));
-
- + if (disable_shim_lock)
- + total_module_size += sizeof (struct grub_module_header);
- +
- if (config_path)
- {
- config_size = ALIGN_ADDR (grub_util_get_image_size (config_path) + 1);
- @@ -1065,6 +1068,16 @@ grub_install_generate_image (const char *dir, const char *prefix,
- offset += dtb_size;
- }
-
- + if (disable_shim_lock)
- + {
- + struct grub_module_header *header;
- +
- + header = (struct grub_module_header *) (kernel_img + offset);
- + header->type = grub_host_to_target32 (OBJ_TYPE_DISABLE_SHIM_LOCK);
- + header->size = grub_host_to_target32 (sizeof (*header));
- + offset += sizeof (*header);
- + }
- +
- if (config_path)
- {
- struct grub_module_header *header;
- --
- 2.14.2
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