Question about the order of FDE steps with LUKS and LVM

submitted by umami_wasabi

I'm setting up FDE and wonders which one is better. "LVM over LUKS" or "LUKS over LVM"? Or something else? Does one is definitely better then the other? What are your preference?

Thanks.

Log in to comment

19 Comments

Max-P

It depends where you want your encryption. If you want all of your LVM volumes to be encrypted at once then you want LVM over LUKS. If you want volumes with different encryption, or no encryption, then you want LUKS over LVM. You can also do LUKS over LVM over LUKS if you must but that's kinda dumb.

LVM over LUKS is more common as generally people want to encrypt everything.

I use ZFS native encryption, so I guess that's closer to LUKS over LVM for personal preference.

umami_wasabi [OP]

Should the LVM partition layout considered as metadata leak in LUKS over LVM?

Max-P

Yes

umami_wasabi [OP]

Should I worried about it?

Max-P

Probably not. The metadata it leaks will be the name of the volumes, their sizes and possibly used space on them.

It really depends on your use case. If you're only using one key, I'd put LVM on top of LUKS just for the simplicity. Otherwise it becomes a threat model analysis: if someone steals your computer or drive, do you care that they know you have 5 volumes on them and roughly how much data is on there?

I need my desktop to boot unattended, and it's got 5 drives in it, so it made sense for me to have separate encryption. It boots and does its NAS duties on its own, then when I log in a dedicated dataset gets mounted for me with all my data on it. From there I might unlock some volumes for work by getting their key from an AWS Secrets Manager endpoint. My laptop is plain f2fs over LUKS.

umami_wasabi [OP]

I'm planning FDE on my laptop which have 2 drives. I originally plan to use LUKS on LVM as I can use LVM to join two drives into one. But now I wonders if my choice is right.

TMP_NKcYUEoM7kXg4qYe , edited

From the info I've gathered, it seems that LUKS over LVM is the "proper" way as ideally you'd only want to encrypt swap, /tmp and /var. (/tmp and /var are places for temporary files, ie. opening a .zip archive. Swap is just RAM on your hard drive, so a place where your passwords could be stored) Encrypting the root (equivalent of "program files" in Windows) won't make your system more secure, just slower. (If you live in a place where you need to keep the list of your installed apps private, you'd probably be fricced by using encryption anyways.) Home directory should obviously be encrypted but for the best performance you should use file level encryption instead of block level.

The thing is that setting it up this way is pretty hard so distros generally use 2 easier methods to setup encryption. Either encrypt the whole disk (LVM over LUKS) or encrypt only the home directory. I wonder whether the latter is secure enough though. Mint for example does not explicitly state that swap, /var and /tmp are encrypted when you select "encrypt home directory" but on Cinnamon there is not hibernation option so there is a chance that Swap is encrypted, just with a one-time password, which gets generated on boot and deleted after shutdown. <--- citation needed...edit: I've just tried hibernating in Mint without FDE and it didn't work, you just get a new session after resuming, so that's good.

Relevant article: https://www.linuxinsider.com/story/the-case-against-full-disk-encryption-86774.html

also: https://wiki.archlinux.org/title/Data-at-rest_encryption#Block_device_vs_stacked_filesystem_encryption

umami_wasabi [OP]

I though FDE is to thwart physical access to exfiltrate and or recover data. Making the root partition unencrypted surely will boost performance but I feel like this opens up an additional avenue for an attacker to exploit and defeat the purpose of doing FDE? It isn't just making "installed apps private" but literally replace some binaries with a backdoored version of it with then enables access to decrypted data.

TMP_NKcYUEoM7kXg4qYe , edited

If an attacker has physical access to your device, you should not use the device afterwards, ever. There are some mitigations like Secure Boot and Heads OS, but they only slow down the attacker. Given enough time, you cannot stop him. Heads OS is pretty much for giving your laptop to airport security temporary and Secure Boot has been hacked in a minute. Although that was using TMP outside of the CPU, I would not trust Secure Boot with TMP 2.0 for anything other than a quick customs check either.

Using FDE as a protection against physical attacks is just a false sense of security. Veracrypt for example go as far as to say that secure boot is false sense of security.

For maximum paranoia there is a use for FDE, though. If you install a crappy app that saves data outside of RAM, /home, /var and /tmp, the data won't get leaked. Though that would be a massive security issue because most linux computers are servers which cannot use FDE.

umami_wasabi [OP], edited

For secure boot bypasses I could only find BlackLotus is the only one capable to do this. I would like to have more details to support the claim "Secure Boot has been hacked in a minute." Also, I would like the explanation on secure boot is a false sense of security and points to suport such claim as BlackLotus is the only publicly known malware to bypass secure boot.

However, I do firmly believe that there ia no reason that servers can't use FDE as they are no differ than other typical computer.

EDIT: forgot the "boot" for secure boot

NaN , edited

I think people tend to get hung up on where you store the key material for a server. Hardware token and TPM being two options that are less secure, but network bound disk encryption is supported as well as a combination. So you could have it require the network key as well as the matching PCRs from the TPM for the proper software load before it will unseal.

Max-P

TPM has been bypassed. Researches found a lot of laptops where you can just attach wires to the TPM communication lines and you can just listen and wait for the TPM to spit out the key.

It's a hardware attack so game over. But still worth doing especially on servers and desktops because then it's still much more of a skilled attack than someone just stealing the drives. Especially servers with their front drive bays you can literally just pop the drive. And if the drive dies and you can't erase it, it's fine, you can throw it away and not care because it's FDE so you can just throw away the keys.

koper , edited

The most common physical attacks will be you misplacing your device or some friend/burglar/cop taking it. FDE works great in those scenarios.

Max-P

If you're not careful /etc can also contain passwords and other sensitive files. My WiFi password is there for example because it needs to be in the wpa_supplicant config file. On servers that's TLS certificates and keys.

In my experience block level is faster, and less of a hassle, and can support hibernation properly. Also much easier if you want just one big partition to not waste space on separate root home and var.

mvirts

i prefer just luck, ie good luck using my crappy credit for anything if you steal my machine 😹.

for real though, i had a family member pass away and getting their crypto keys was problematic despite good planning on their part. Does anyone else have a plan for passing on access to encrypted data?