90 lines
2.9 KiB
Diff
90 lines
2.9 KiB
Diff
|
From b7e2fb6a680447b7bb7eb18bb7570afa8d2b7f09 Mon Sep 17 00:00:00 2001
|
||
|
|
From: Gary Lin <glin@suse.com>
|
||
|
|
Date: Thu, 10 Aug 2023 10:19:29 +0800
|
||
|
|
Subject: [PATCH 4/4] diskfilter: look up cryptodisk devices first
|
||
|
|
|
||
|
|
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>
|
||
|
|
---
|
||
|
|
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 61a311efd..94832c8dd 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
|
||
|
|
|