blog: add sealed images deploying post

Fourth post in the sealed images series, covering deployment via
bcvk and verification that the full security chain is active.

Assisted-by: OpenCode (claude-opus-4-6)
Signed-off-by: John Eckersberg <jeckersb@redhat.com>

Author: jeckersb

content/blog/2026-apr-30-sealed-images-deploying.md

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+title = "Sealed images: deploying and verifying a sealed image"
+date = 2026-04-30
+slug = "2026-apr-30-sealed-images-deploying"
+
+[extra]
+author = "jeckersb"
++++
+
+# Sealed images: deploying and verifying a sealed image
+
+In the [previous post](@/blog/2026-apr-29-sealed-images-building.md)
+we built a sealed, signed container image.  Now it's time to deploy
+it to a virtual machine and verify that the full security chain is
+active.
+
+## bcvk: a tool for running bootc VMs
+
+[bcvk](https://github.com/bootc-dev/bcvk) (bootc virtualization kit)
+is a tool that makes it easy to run bootc container images as virtual
+machines.  Under the hood, it calls `bootc install to-disk` to create
+a bootable disk image, then manages the VM lifecycle via libvirt.
+For sealed images, bcvk also handles Secure Boot key enrollment into
+the VM's UEFI firmware automatically using
+[virt-firmware](https://gitlab.com/kraxel/virt-firmware).
+
+bcvk is available as a package on Fedora and EPEL:
+
+```
+$ dnf install bcvk
+```
+
+## Deploying the image
+
+With the sealed image built from the previous post and keys generated
+from the key management post, deploying is a single command:
+
+```
+$ bcvk libvirt run \
+    --ssh-wait \
+    --name sealed-demo \
+    --filesystem=ext4 \
+    --secure-boot-keys target/keys \
+    localhost/sealed-host:latest
+```
+
+Let's break down what's happening here:
+
+- `--filesystem=ext4` tells `bootc install` to use ext4 for the root
+  filesystem.  The default root filesystem may be XFS, which does not
+  support fs-verity, so we explicitly select ext4 here.  (fs-verity
+  is supported on ext4 and btrfs.)
+- `--secure-boot-keys target/keys` points bcvk to the directory
+  containing our PK, KEK, and db certificates.  bcvk uses
+  `virt-fw-vars` to enroll these keys into a copy of the OVMF
+  firmware variable store, so the VM boots with Secure Boot enabled
+  and configured to trust our signing key.
+- `--ssh-wait` tells bcvk to wait until SSH is available before
+  returning, so we know the system has fully booted.
+
+If you're using the
+[examples repository](https://github.com/redhat-cop/rhel-bootc-examples/tree/main/sealing),
+this is wrapped up in a convenient `just` recipe:
+
+```
+$ just bcvk-ssh
+```
+
+This builds the image, boots the VM, waits for it to reach
+`multi-user.target`, and opens an interactive SSH session.
+
+## Verifying the seal
+
+Once the system is booted and we have an SSH session, we can verify
+that the full security chain is active.
+
+### Check the kernel command line
+
+```
+$ cat /proc/cmdline
+composefs=3a7f... (128-character SHA-512 hex digest) rw
+```
+
+The presence of `composefs=<digest>` in the kernel command line
+confirms that the initramfs received the composefs digest from the
+signed UKI.  This is the digest that was computed during the build
+and embedded in the UKI's command line section.
+
+### Check the root mount
+
+```
+$ findmnt -t overlay /
+TARGET SOURCE                    FSTYPE  OPTIONS
+/      overlay[/sysroot/state..] overlay ro,relatime,...,verity=require,...
+```
+
+The key thing to look for is `verity=require` in the mount options.
+This confirms that the kernel is enforcing fs-verity verification
+on every file access through the composefs mount.  Any file in the
+operating system whose content doesn't match its expected fs-verity
+digest will produce an I/O error when read.
+
+### Check Secure Boot status
+
+```
+$ mokutil --sb-state
+SecureBoot enabled
+```
+
+This confirms that the firmware verified the bootloader and UKI
+signatures before allowing them to execute.
+
+### What this tells us
+
+These three checks together confirm the full chain from the
+[first post](@/blog/2026-apr-27-sealed-images-security-chain.md):
+
+1. Secure Boot verified the bootloader and UKI (`mokutil --sb-state`)
+2. The UKI delivered the composefs digest to the initramfs
+   (`/proc/cmdline`)
+3. The kernel is enforcing per-file verification against that digest
+   (`verity=require`)
+
+## What happens if something is tampered with?
+
+It's worth understanding why tampering with a sealed system is
+difficult in practice.
+
+The operating system files are stored in a content-addressed object
+store on disk.  Each object has fs-verity enabled, which means the
+kernel has recorded a cryptographic hash of its contents.  The files
+are immutable: you cannot write to an fs-verity protected file.  Any
+attempt to open a verity-protected file for writing will fail.
+
+Even if an attacker were to bypass the filesystem and corrupt data
+directly on the underlying block device, the kernel would detect
+the corruption.  When a process attempts to read the tampered file,
+the kernel verifies the data against the stored hash before
+returning it.  If the data doesn't match, the read fails with
+`EIO`.  The corrupted data is never served to any process.
+
+This is a meaningful distinction from a system where tampered files
+are silently served.  On a sealed system, corruption doesn't go
+unnoticed -- it causes an immediate, visible failure.
+
+## Conclusion
+
+Over the course of this series, we've walked through the complete
+lifecycle of a sealed image:
+
+1. [The security chain](@/blog/2026-apr-27-sealed-images-security-chain.md)
+   from firmware to filesystem that makes sealed images possible
+2. [Key management](@/blog/2026-apr-28-sealed-images-key-management.md)
+   for generating and enrolling Secure Boot keys
+3. [Building a sealed image](@/blog/2026-apr-29-sealed-images-building.md)
+   with a multi-stage container build
+4. Deploying and verifying the seal (this post)
+
+The complete working example is available in the
+[rhel-bootc-examples](https://github.com/redhat-cop/rhel-bootc-examples)
+repository under the
+[sealing](https://github.com/redhat-cop/rhel-bootc-examples/tree/main/sealing)
+directory.