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[PATCH v12 18/20] diskfilter: look up cryptodisk devices first
From: |
Gary Lin |
Subject: |
[PATCH v12 18/20] diskfilter: look up cryptodisk devices first |
Date: |
Fri, 19 Apr 2024 16:31:02 +0800 |
When using disk auto-unlocking with TPM 2.0, the typical grub.cfg may
look like this:
tpm2_key_protector_init --tpm2key=(hd0,gpt1)/boot/grub2/sealed.tpm
cryptomount -u <PART-UUID> -P tpm2
search --fs-uuid --set=root <FS-UUID>
Since the disk search order is based on the order of module loading, the
attacker could insert a malicious disk with the same FS-UUID root to
trick grub2 to boot into th malicious root and further dump memory to
steal the unsealed key.
To defend such attack, we can specify the hint provided by 'grub-probe'
to search the encrypted partition first:
search --fs-uuid --set=root --hint='cryptouuid/<PART-UUID>' <FS-UUID>
However, for LVM on a encrypted partition, the search hint provided by
'grub-probe' is:
--hint='lvmid/<VG-UUID>/<LV-UUID>'
It doesn't guarantee to look up the logical volume from the encrypted
partition, so the attacker may have the chance to fool grub2 to boot
into the malicious disk.
To mininize the attack surface, this commit tweaks the disk device search
in diskfilter to look up cryptodisk devices first and then others, so
that the auto-unlocked disk will be found first, not the attacker's disk.
Signed-off-by: Gary Lin <glin@suse.com>
Cc: Fabian Vogt <fvogt@suse.com>
---
grub-core/disk/diskfilter.c | 35 ++++++++++++++++++++++++++---------
1 file changed, 26 insertions(+), 9 deletions(-)
diff --git a/grub-core/disk/diskfilter.c b/grub-core/disk/diskfilter.c
index 21e239511..df1992305 100644
--- a/grub-core/disk/diskfilter.c
+++ b/grub-core/disk/diskfilter.c
@@ -226,15 +226,32 @@ scan_devices (const char *arname)
int need_rescan;
for (pull = 0; pull < GRUB_DISK_PULL_MAX; pull++)
- for (p = grub_disk_dev_list; p; p = p->next)
- if (p->id != GRUB_DISK_DEVICE_DISKFILTER_ID
- && p->disk_iterate)
- {
- if ((p->disk_iterate) (scan_disk_hook, NULL, pull))
- return;
- if (arname && is_lv_readable (find_lv (arname), 1))
- return;
- }
+ {
+ /* look up the crytodisk devices first */
+ for (p = grub_disk_dev_list; p; p = p->next)
+ if (p->id == GRUB_DISK_DEVICE_CRYPTODISK_ID
+ && p->disk_iterate)
+ {
+ if ((p->disk_iterate) (scan_disk_hook, NULL, pull))
+ return;
+ if (arname && is_lv_readable (find_lv (arname), 1))
+ return;
+ break;
+ }
+
+ /* check the devices other than crytodisk */
+ for (p = grub_disk_dev_list; p; p = p->next)
+ if (p->id == GRUB_DISK_DEVICE_CRYPTODISK_ID)
+ continue;
+ else if (p->id != GRUB_DISK_DEVICE_DISKFILTER_ID
+ && p->disk_iterate)
+ {
+ if ((p->disk_iterate) (scan_disk_hook, NULL, pull))
+ return;
+ if (arname && is_lv_readable (find_lv (arname), 1))
+ return;
+ }
+ }
scan_depth = 0;
need_rescan = 1;
--
2.35.3
- [PATCH v12 00/20] Automatic Disk Unlock with TPM2, Gary Lin, 2024/04/19
- [PATCH v12 01/20] posix_wrap: tweaks in preparation for libtasn1, Gary Lin, 2024/04/19
- [PATCH v12 03/20] libtasn1: disable code not needed in grub, Gary Lin, 2024/04/19
- [PATCH v12 02/20] libtasn1: import libtasn1-4.19.0, Gary Lin, 2024/04/19
- [PATCH v12 04/20] libtasn1: changes for grub compatibility, Gary Lin, 2024/04/19
- [PATCH v12 05/20] libtasn1: fix the potential buffer overrun, Gary Lin, 2024/04/19
- [PATCH v12 09/20] key_protector: Add key protectors framework, Gary Lin, 2024/04/19
- [PATCH v12 06/20] libtasn1: compile into asn1 module, Gary Lin, 2024/04/19
- [PATCH v12 10/20] tpm2: Add TPM Software Stack (TSS), Gary Lin, 2024/04/19
- [PATCH v12 18/20] diskfilter: look up cryptodisk devices first,
Gary Lin <=
- [PATCH v12 20/20] tests: Add tpm2_test, Gary Lin, 2024/04/19
- [PATCH v12 11/20] key_protector: Add TPM2 Key Protector, Gary Lin, 2024/04/19
- [PATCH v12 07/20] asn1_test: test module for libtasn1, Gary Lin, 2024/04/19
- [PATCH v12 08/20] libtasn1: Add the documentation, Gary Lin, 2024/04/19
- [PATCH v12 12/20] cryptodisk: Support key protectors, Gary Lin, 2024/04/19