[PATCH v7 28/29] docs/specs: Add secure IPL documentation

[Zhuoying Cai <zycai@linux.ibm.com>]

Add documentation for secure IPL

Signed-off-by: Collin Walling <walling@linux.ibm.com>
---
 docs/specs/s390x-secure-ipl.rst | 55 +++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/docs/specs/s390x-secure-ipl.rst b/docs/specs/s390x-secure-ipl.rst
index 70388d77d8..45f58ab49d 100644
--- a/docs/specs/s390x-secure-ipl.rst
+++ b/docs/specs/s390x-secure-ipl.rst
@@ -1,5 +1,60 @@
 .. SPDX-License-Identifier: GPL-2.0-or-later
 
+s390 Secure IPL
+===============
+
+Secure IPL (a.k.a. secure boot) enables s390-ccw virtual machines to
+leverage qcrypto libraries and z/Architecture emulations to verify the
+integrity of signed kernels. The qcrypto libraries are used to perform
+certificate validation and signature-verification, whereas the
+z/Architecture emulations are used to ensure secure IPL data has not
+been tampered with, convey data between QEMU and userspace, and set up
+the relevant secure IPL data structures with verification results.
+
+To find out more about using this feature, see
+``docs/system/s390x/secure-ipl.rst``.
+
+Note that "userspace" will refer to the s390-ccw BIOS unless stated
+otherwise.
+
+Both QEMU and userspace work in tandem to perform secure IPL. The Secure
+Loading Attributes Facility (SCLAF) is used to check the Secure Code
+Loading Attribute Block (SCLAB) and ensure that secure IPL data has not
+been tampered with. DIAGNOSE 'X'320' is invoked by userspace to query
+the certificate store info and retrieve specific certificates from QEMU.
+DIAGNOSE 'X'508' is used by userspace to leverage qcrypto libraries to
+perform signature-verification in QEMU. Lastly, userspace generates and
+appends an IPL Information Report Block (IIRB) at the end of the IPL
+Parameter Block, which is used by the kernel to store signed and
+verified entries.
+
+The logical steps are as follows:
+
+- Userspace reads data payload from disk (e.g. stage3 boot loader, kernel)
+- Userspace checks the validity of the SCLAB
+- Userspace invokes DIAG 508 subcode 1 and provides it the payload
+- QEMU handles DIAG 508 request by reading the payload and retrieving the
+  certificate store
+- QEMU DIAG 508 utilizes qcrypto libraries to perform signature-verification on
+  the payload, attempting with each cert in the store (until success or
+  exhausted)
+- QEMU DIAG 508 returns:
+
+  - success: index of cert used to verify payload
+  - failure: error code
+
+- Userspace responds to this operation:
+
+  - success: retrieves cert from store via DIAG 320 using returned index
+  - failure: reports with warning (audit mode), aborts with error (secure mode)
+
+- Userspace appends IIRB at the end of the IPLB
+- Userspace kicks off IPL
+
+More information regarding the respective DIAGNOSE commands and IPL data
+structures are outlined within this document.
+
+
 s390 Certificate Store and Functions
 ====================================
 
-- 
2.51.1