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[PATCH v10 18/20] diskfilter: look up cryptodisk devices first
From: |
Gary Lin |
Subject: |
[PATCH v10 18/20] diskfilter: look up cryptodisk devices first |
Date: |
Tue, 9 Apr 2024 16:30:50 +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 v10 09/20] key_protector: Add key protectors framework, (continued)
- [PATCH v10 09/20] key_protector: Add key protectors framework, Gary Lin, 2024/04/09
- [PATCH v10 10/20] tpm2: Add TPM Software Stack (TSS), Gary Lin, 2024/04/09
- [PATCH v10 11/20] key_protector: Add TPM2 Key Protector, Gary Lin, 2024/04/09
- [PATCH v10 12/20] cryptodisk: Support key protectors, Gary Lin, 2024/04/09
- [PATCH v10 13/20] util/grub-protect: Add new tool, Gary Lin, 2024/04/09
- [PATCH v10 15/20] tpm2: Implement NV index, Gary Lin, 2024/04/09
- [PATCH v10 14/20] tpm2: Support authorized policy, Gary Lin, 2024/04/09
- [PATCH v10 16/20] cryptodisk: Fallback to passphrase, Gary Lin, 2024/04/09
- [PATCH v10 18/20] diskfilter: look up cryptodisk devices first,
Gary Lin <=
- [PATCH v10 17/20] cryptodisk: wipe out the cached keys from protectors, Gary Lin, 2024/04/09
- [PATCH v10 19/20] tpm2: Enable tpm2 module for grub-emu, Gary Lin, 2024/04/09
- [PATCH v10 20/20] tests: Add tpm2_test, Gary Lin, 2024/04/09
- Re: [PATCH v10 00/20] Automatic Disk Unlock with TPM2, Gary Lin, 2024/04/12