[PATCH] os: deprecate the -enable-fips option and QEMU's FIPS enforcement

["Daniel P. Berrangé" <berrange@redhat.com>]

The -enable-fips option was added a long time ago to prevent the use of
single DES when VNC when FIPS mode is enabled. It should never have been
added, because apps are supposed to unconditionally honour FIPS mode
based on the '/proc/sys/crypto/fips_enabled' file contents.

In addition there is more to achieving FIPS compliance than merely
blocking use of certain algorithms. Those algorithms which are used
need to perform self-tests at runtime.

QEMU's built-in cryptography provider has no support for self-tests,
and neither does the nettle library.

If QEMU is required to be used in a FIPS enabled host, then it must be
built with the libgcrypt library enabled, which will unconditionally
enforce FIPS compliance in any algorithm usage.

Thus there is no need to keep either the -enable-fips option in QEMU, or
QEMU's internal FIPS checking methods.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 docs/system/deprecated.rst | 11 +++++++++++
 os-posix.c                 |  3 +++
 2 files changed, 14 insertions(+)

diff --git a/docs/system/deprecated.rst b/docs/system/deprecated.rst
index 905628f3a0..faa2bc49b1 100644
--- a/docs/system/deprecated.rst
+++ b/docs/system/deprecated.rst
@@ -158,6 +158,17 @@ devices.  It is possible to use drives the board doesn't pick up with
 -device.  This usage is now deprecated.  Use ``if=none`` instead.
 
 
+``--enable-fips`` (since 5.2)
+
+This option restricts usage of certain cryptographic algorithms when
+the host is operating in FIPS mode.
+
+If FIPS compliance is required, QEMU should be built with the ``libgcrypt``
+library enabled as a cryptography provider.
+
+Neither the ``nettle`` library, or the built-in cryptography provider are
+supported on FIPS enabled hosts.
+
 QEMU Machine Protocol (QMP) commands
 ------------------------------------
 
diff --git a/os-posix.c b/os-posix.c
index 1de2839554..a6846f51c1 100644
--- a/os-posix.c
+++ b/os-posix.c
@@ -153,6 +153,9 @@ int os_parse_cmd_args(int index, const char *optarg)
         break;
 #if defined(CONFIG_LINUX)
     case QEMU_OPTION_enablefips:
+        warn_report("-enable-fips is deprecated, please build QEMU with "
+                    "the `libgcrypt` library as the cryptography provider "
+                    "to enable FIPS compliance");
         fips_set_state(true);
         break;
 #endif
-- 
2.26.2