SEV-ES with LUKS

Kickstart file to install Fedora 37 with luks encrypted root

login is root:root
luks passphrase is MY-LUKS-PASSPHRASE
/etc/crypttab setup to autounlock LUKS when we inject SEV secret

luks.ks:

rootpw --plaintext root
firstboot --disable
timezone America/New_York --utc
keyboard --vckeymap=us --xlayouts='us'
lang en_US.UTF-8
reboot
text
skipx

ignoredisk --only-use=vda
clearpart --all --initlabel --disklabel=gpt --drives=vda
part /boot/efi --size=512 --fstype=efi
part /boot --size=512 --fstype=xfs --label=boot
part / --fstype="xfs" --ondisk=vda --encrypted --label=root --luks-version=luks2 --grow --passphrase MY-LUKS-PASSPHRASE

%packages
@^server-product-environment
%end

%post
# Set the secret path as a crypttab keyfile
# Append `keyfile-erase` option to unlink it after unlock
cat /etc/crypttab | awk '{print $1" "$2" /sys/kernel/security/secrets/coco/736869e5-84f0-4973-92ec-06879ce3da0b "$4",keyfile-erase"}' | tee /etc/crypttab
# Put `efi_secret` driver in the initrd
echo 'add_drivers+=" efi_secret "' > /etc/dracut.conf.d/99-efi_secret.conf
# Trigger initrd rebuild
dnf reinstall -y kernel\*
%end

Install the VM on f36 host with the following differences:

latest libvirt-daemon-kvm, qemu-system-x86, edk2-ovmf from virt-preview repo
cargo install sevctl
virt-manager/virt-install from git as of Nov 27 2022
libvirt.git as of Nov 27 2022

# virt-preview packages on f36 host:
# $ rpm -q libvirt-daemon qemu-system-x86 edk2-ovmf
# libvirt-daemon-8.8.0-1.fc36.x86_64
# qemu-system-x86-7.1.0-3.fc36.x86_64
# edk2-ovmf-20220826gitba0e0e4c6a17-1.fc36.noarch

# libvirt.git as of Nov 27 2022
VALIDATE="$HOME/src/libvirt/tools/virt-qemu-sev-validate"

# From virt-manager.git
VIRTXML="$HOME/src/virt-manager/virt-xml"
VIRTINSTALL="$HOME/src/virt-manager/virt-install"

VMNAME=lukstest

# Install the VM, full automated
# SEV is not enabled at this point
sudo $VIRTINSTALL \
    --name $VMNAME --ram 8096 --disk size=20 \
    --nographics \
    --location https://dl.fedoraproject.org/pub/fedora/linux/development/37/Server/x86_64/os/ \
    --noreboot \
    --initrd-inject luks.ks \
    --extra-args "inst.ks=file:/luks.ks console=ttyS0" \
    --tpm none \
    --boot firmware=efi,loader.stateless=yes \
    --memorybacking locked=on \
    --launchSecurity sev,policy=$POLICY,kernelHashes=on,session=$SESSION,dhCert=$DHCERT \
    --debug

Now we extract the kernel + initrd + cmdline. This needs to be done every time the kernel is updated inside the VM. You should be prompted for the LUKS password.

sudo virt-get-kernel -d $VMNAME --prefix $VMNAME > get-kernel.txt
KERNEL=$(basename $(cat get-kernel.txt | grep vmlin | cut -f4 -d ' '))
INITRD=$(basename $(cat get-kernel.txt | grep initr | cut -f4 -d ' '))
sudo mv $KERNEL $INITRD /var/lib/libvirt/images

# Pull kernel cmdline out of /boot/loader/entries
sudo virt-copy-out -d $VMNAME /boot/loader/entries .
sudo chown $UID entries
CMDLINE=$(sudo cat entries/* | grep options | tail -1 | cut -f 2- -d ' ')

# Update VM config to boot off external kernel+initrd
sudo $VIRTXML $VMNAME --edit \
    --boot kernel=/var/lib/libvirt/images/$KERNEL,initrd=/var/lib/libvirt/images/$INITRD,cmdline="$CMDLINE"

The following is the validation process.

Session blob must be regenerated for every VM run
Ensure SEV is enabled in the VM config and appropriate firmware config is used
Use virt-qemu-sev-validate to inject the LUKS key

POLICY=5
CERTDIR=$HOME/src/sevcerts/$VMNAME
SEVCTL=$HOME/.cargo/bin/sevctl

# Generate SEV VM config. Must be run on SEV host
rm -rf $CERTDIR; mkdir -p $CERTDIR
sudo $SEVCTL export -f $CERTDIR/sevctl-export.chain
sudo $SEVCTL session $CERTDIR/sevctl-export.chain $POLICY --name $CERTDIR/$VMNAME
DHCERT=`cat $CERTDIR/${VMNAME}_godh.b64`
SESSION=`cat $CERTDIR/${VMNAME}_session.b64`

# Enable SEV and insert session info into the XML
sudo $VIRTXML $VMNAME --edit \
    --launchSecurity sev,policy=$POLICY,kernelHashes=on,session=$SESSION,dhCert=$DHCERT

# Switch to OVMF.amdsev.fd firmware
sudo rm -rf /var/lib/libvirt/qemu/nvram/${VMNAME}_VARS.fd
sudo $VIRTXML $VMNAME --edit \
    --boot firmware=efi,loader.stateless=yes

# Validate the VM
echo -n MY-LUKS-PASSPHRASE > $HOME/secret.txt
sudo virsh start --paused $VMNAME

sudo $VALIDATE \
--domain $VMNAME \
--tek $CERTDIR/${VMNAME}_tek.bin \
--tik $CERTDIR/${VMNAME}_tik.bin \
--inject-secret 736869e5-84f0-4973-92ec-06879ce3da0b:$HOME/secret.txt \
--insecure \
--debug

# Should go to login prompt, no LUKS passphrase needed
sudo virsh console $VMNAME

crobinso/sev_with_luks.md