[PULL 35/37] docs/system/s390x: Add secure IPL documentation

[Eric Farman <farman@linux.ibm.com>]

From: Zhuoying Cai <zycai@linux.ibm.com>

Add documentation for secure IPL

Signed-off-by: Collin Walling <walling@linux.ibm.com>
Signed-off-by: Zhuoying Cai <zycai@linux.ibm.com>
Reviewed-by: Joshua Daley <jdaley@linux.ibm.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Link: https://lore.kernel.org/qemu-devel/20260730214624.2328883-34-zycai@linux.ibm.com
Signed-off-by: Eric Farman <farman@linux.ibm.com>
---
 docs/system/s390x/secure-ipl.rst | 103 +++++++++++++++++++++++++++++++
 1 file changed, 103 insertions(+)

diff --git a/docs/system/s390x/secure-ipl.rst b/docs/system/s390x/secure-ipl.rst
index c8fb887ac0..67de20f47a 100644
--- a/docs/system/s390x/secure-ipl.rst
+++ b/docs/system/s390x/secure-ipl.rst
@@ -1,5 +1,22 @@
 .. SPDX-License-Identifier: GPL-2.0-or-later
 
+s390 Secure IPL
+===============
+
+Secure IPL, also known as secure boot, enables s390-ccw virtual machines to
+verify the integrity of guest kernels.
+
+For technical details of this feature, see the
+:doc:`specs document </specs/s390x-secure-ipl>`.
+
+This document explains how to use secure IPL with s390x in QEMU. It covers
+the command line options for providing certificates and enabling secure IPL,
+the different IPL modes (Normal, Audit, and Secure), and system requirements.
+
+A quickstart guide is provided to demonstrate how to generate certificates,
+sign images, and start a guest in Secure Mode.
+
+
 Secure IPL Command Line Options
 -------------------------------
 
@@ -79,3 +96,89 @@ Configuration:
 .. code-block:: shell
 
     qemu-system-s390x -machine s390-ccw-virtio,secure-boot=on,boot-certs.0.path=/.../qemu/certs,boot-certs.1.path=/another/path/cert.pem ...
+
+
+Constraints
+-----------
+
+The following constraints apply when attempting to boot an s390x guest in secure
+mode:
+
+- z16 or "qemu" CPU model
+- certificates must be in X.509 PEM format
+- only support for SCSI scheme of virtio-blk/virtio-scsi devices
+- a boot device must be specified
+- any unsupported devices (e.g., ECKD and VFIO) or non-eligible devices (e.g.,
+  network) will cause the entire boot process to terminate early, with an error
+  logged to the console.
+
+
+Secure IPL Quickstart
+---------------------
+
+Build QEMU with gnutls enabled
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: shell
+
+    ./configure … --enable-gnutls
+
+Generate certificate (e.g. via certtool)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+A private key is required before generating a certificate. This key must be kept
+secure and confidential.
+
+Use an RSA private key for signing.
+
+.. code-block:: shell
+
+    certtool --generate-privkey > key.pem
+
+A self-signed certificate requires the organization name. Use the ``cert.info``
+template to pre-fill values and avoid interactive prompts from certtool.
+
+.. code-block:: shell
+
+    cat > cert.info <<EOF
+    cn = "My Name"
+    expiration_days = 365
+    cert_signing_key
+    EOF
+
+    certtool --generate-self-signed \
+             --load-privkey key.pem \
+             --template cert.info \
+             --hash=SHA256 \
+             --outfile cert.pem
+
+Sign Images (e.g. via sign-file)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+- signing must be performed on a guest filesystem
+- sign-file script used in the example below is located within the kernel source
+  repo
+
+.. code-block:: shell
+
+    ./sign-file sha256 key.pem cert.pem /boot/vmlinuz-…
+    ./sign-file sha256 key.pem cert.pem /usr/lib/s390-tools/stage3.bin
+
+Note: re-signing a component will not verify correctly; the existing signature
+must be stripped before a new one is applied.
+
+Run zipl with secure boot enabled
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+- zipl must be performed on a guest filesystem
+
+.. code-block:: shell
+
+    zipl --secure 1 -V
+
+Command line options for starting the guest
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: shell
+
+    qemu-system-s390x -machine s390-ccw-virtio,secure-boot=on,boot-certs.0.path=cert.pem ...
-- 
2.55.0