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
---
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;