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Re: Support for plain dm-crypt and detached LUKS header

From: Andrei Borzenkov
Subject: Re: Support for plain dm-crypt and detached LUKS header
Date: Sun, 9 Apr 2017 09:29:29 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0

Thank you for the patch. Unfortunately it does not solve fundamental
problem - grub-install is expected to auto-detect everything that is
required to access /boot/grub (it violates it now for encrypted /boot,
but I plan to submit patch after release to decouple it from
/etc/default/grub). So any solution that integrates plain
dm-crypt/detached header into grub-install needs to work without user
intervention and provides some means to auto-detect this.

Although we already have some options that cannot be autodetected (e.g.
keys). So may be this can be relaxed.

But at the very least it needs to check whether LUKS device has detached
header and abort by default if it has, otherwise we cannot even find
device to open at boot time. It also needs code to detect underlying
block device and again abort if partition map does not support PTUUID
(i.e. is not MSDOS or GPT), as this is the only means to find it.

In generally, if grub-install completed without error grub should boot -
otherwise we have a bug.

08.04.2017 19:16, Mat628 пишет:
> Hi, I'd like to first say thanks to the additions you made to cryptomount. I 
> came across your patches 2-3 months ago when I was looking to do FDE 
> including /boot for LVM on LUKS. I created a few patches outlined with their 
> features below. I would have messaged sooner but I didn't know about these 
> posts on grub-help until after finding the link from your github. After also 
> coming across the problem of having no way to reliably predict what a device 
> (hd0,msdos1) will map to, I ended up creating an add-on command, that uses 
> the partition UUID/GUID, to search (--pt-uuid) and an accompanying module 
> search.pt_uuid. These two commands mirror the search --fs-uuid and 
> search.fs_uuid where given a uuid it will return the device. When given a 
> disk/partition UUID/GUID that corresponds to a disk that is either a biosdisk 
> or efidisk, or a partition with a partmap name of either "msdos" or "gpt" on 
> one of the previous disks it will return that device.
> Patch 1 stops search from printing same device twice if called multiple times.
> Patch 2 allows this--->Added module search_pt_uuid. When given a disk/part 
> UUID/GUID it will return the associated device.
> On a biosdisk/mbr it will return the same value for the device 
> (hd0)/(hd0,msdos1) as lsblk -o PARTUUID returns. This should be the same as 
> the NT disk signature located at mbr.code[440] for 4 bytes in little endian 
> format plus the partition number appended if applicable xxxxxxxx-yy. On an 
> efidisk/gpt it will return the same value for the device (hd0)/(hd0,gpt1) as 
> lsblk -o PARTUUID returns. This will be the disk/partition UUID/GUID.
> An example of using this command inside load.cfg or directly on the grub 
> command line. This example is for a detached header LUKS volume on 
> (hdX,msdosY) which corresponds to a partuuid of 12345678-01 with the header 
> file stored on a plain text partition either on the same device or a 
> different one with a fs_uuid=5432-7654.
> From your site this would look like
> cryptomount -H (hd0,1)/header hd1,1
> But with my patch it would be.
> search.fs_uuid 5432-7654 header_file_device ----Line for setting (hd0,1)
> search.pt_uuid 12345678-01 cryptodevice ----Line for setting (hd1,1)
> cryptomount ($cryptodevice) --header=($header_file_device)/header.bin
> Or if the header file is in a separate encrypted LUKS volume. LUKS volume 
> UUID is 12345678-1234-1234-1234-1234567890ab. When the LUKS volume is open 
> the mounted fs_uuid is 11112222-3333-4444-5555-123456654321 for a ext4 
> partition.
> cryptomount -u 12345678-1234-1234-1234-1234567890ab ----Line for opening the 
> LUKS volume with the header file in it.
> search.fs_uuid 11112222-3333-4444-5555-123456654321 header_file_device 
> ----Line for setting (hd0,1)
> search.pt_uuid 12345678-01 cryptodevice ----Line for setting (hd1,1)
> cryptomount ($cryptodevice) --header=($header_file_device)/header.bin 
> ----Line for opening LUKS volume with /boot
> Patch 3 allows this---->Inclusion of altered "load.cfg" to 
> grub-install/mkconfig.
> mattle_opts (More Advanced Than Traditional LUKS Encryption Options). Added 
> mattle_opts.cfg file which allows the user to customize load.cfg to allow for 
> extra options for cryptomount. mattle_opts.cfg is located in 
> user-defined/etc/ folder. Same folder as crypttab and fstab. Only affects 
> cryptomount options in load.cfg and only if 
> GRUB_ENABLE_CRYPTODISK_MATTLE_OPTS=y is set in grub.cfg. If not set then 
> normal 'cryptomount -u $uuid' is printed to load.cfg. I altered grub-install 
> and grub-mkconfig to allow it to have essentially an alternate load.cfg 
> (mattle_opts.cfg) to be easily editted by the user prior to running 
> grub-install to allow grub-install to then read from this file and then 
> fprint this alternate files contents into load.cfg to allow your alternate 
> cryptomount commands to be run during boot up. This does not interfere with 
> any of grub-install's other actions with load.cfg it merely replaces the 
> normal 'cryptomount -u $uuid' that is printed from grub-install into 
> load.cfg. This makes it so you don't have to do grub-mkimage and the 
> associated commands. Also added command line options for 
> grub-install/mkconfig to allow an alternate mattle_opts.cfg to allow the user 
> to quickly install grub to another device without having to modify the 
> default mattle_opts.cfg.
> Patch 4 allows this----> grub-install and grub-mkconfig magic for /boot on a 
> detached header LUKS volume
> Added grub-install magic for a crypto-device that is on a disk with either an 
> msdos or gpt partition table and either on a biosdisk or efidisk. 
> Grub-install magic works with grub-mkconfig for booting a detached header 
> LUKS volume when used with --crypto-device and --crypto-header. By reading 
> the actual header file that corresponds to that partitcular LUKS volume this 
> allows grub-install/mkconfig to have the proper modules loaded by grub. The 
> grub-install command for /boot located on /dev/sda1 where /dev/sda1 is a 
> detached header LUKS volume and the header is located on the root / directory 
> and we are installing to /dev/sda.
> grub-install --boot-directory=/boot --crypto-device=/dev/sda1 
> --crypto-header=/header.bin /dev/sda
> grub-mkconfig -o /boot/grub/grub.cfg
> For above patch 4 grub-install needs to be run prior to grub-mkconfig so the 
> proper *.cfg files are created and configured to allow cryptodisk.c and luk.c 
> to create a cryptodisk based off the stated crypto-device.
> A few notes: mattle_opts.cfg is read only by grub-install/mkconfig and must 
> be edited outside of grub using nano/text editor.
> The command line options for grub-install do not alter mattle_opts.cfg so if 
> installing to two different devices i.e a usb stick and a hard drive, 
> mattle_opts.cfg may need to be edited. i.e. depending on where header/key 
> files are stored.
> The easiest setup seems to be /boot/grub on the rootfs and only have the 
> applicable header/key files on the usb either in plain text or in an 
> encrypted partition, and have the boot.img and core.img installed to the usb 
> as well.
> The changes to luks.c should only be in effect for grub utils and not in 
> effect during booting.
> I've also included your first 3 LUKS patches as they would apply after my 
> patches. These patches are based off of grub-2.02-rc2. I tested these to work 
> on x64 version of Ubuntu 16.04 LTS running bios. For the efi with gpt it was 
> tested on a virtual machine x64 Ubuntu 16.04 LTS.
> Best regards,
> Matt
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