[Skiboot] [RFC 7/8] secvar/backend: add a switchable-mode edk2-based backend

[Eric Richter]

This patch introduces a new backend driver that wraps the existing
edk2-compat-v1 driver and the new edk2-compat-static driver, to switch
functionality based on the secure boot mode as exposed by the secboot_tpm
storage driver.

If the secure boot mode is set to SYSTEM_MODE, all hooks will be passed to
the edk2-compat-static driver. Otherwise, if the mode is USER_MODE, the
regular edk2-compat-v1 driver hooks are called.

As with the secboot_tpm_switchable driver, asserting physical presence
will switch between modes: clear-os-keys will disable secure boot and enter
USER_MODE, while reset-default-keys will enforce secure boot with default
keys via the edk2-compat-static driver.

RFC NOTE: I don't like how this driver has to directly interact with a
specific storage driver. I am considering instead leaving a crumb in the
device tree for this driver to inspect. That way, if documented as an
interface, a future "switchable" storage driver may also be compatible
with this switchable backend driver.

The name "switchable" is subject to change, I did not put a lot of time
into coming up with good names, so consider all of them placeholders.

Signed-off-by: Eric Richter <erichte at linux.ibm.com>
---
 include/secvar.h                        |  1 +
 libstb/secvar/backend/Makefile.inc      |  2 +-
 libstb/secvar/backend/edk2-switchable.c | 46 +++++++++++++++++++++++++
 3 files changed, 48 insertions(+), 1 deletion(-)
 create mode 100644 libstb/secvar/backend/edk2-switchable.c

diff --git a/include/secvar.h b/include/secvar.h
index 3b439eaf..2aa52ec2 100644
--- a/include/secvar.h
+++ b/include/secvar.h
@@ -41,6 +41,7 @@ extern struct secvar_storage_driver secboot_tpm_driver;
 extern struct secvar_storage_driver secboot_tpm_switchable_driver;
 extern struct secvar_backend_driver edk2_compatible_v1;
 extern struct secvar_backend_driver edk2_compatible_v1_static;
+extern struct secvar_backend_driver edk2_switchable_driver;
 
 int secvar_main(struct secvar_storage_driver, struct secvar_backend_driver);
 
diff --git a/libstb/secvar/backend/Makefile.inc b/libstb/secvar/backend/Makefile.inc
index b929769f..b60efe83 100644
--- a/libstb/secvar/backend/Makefile.inc
+++ b/libstb/secvar/backend/Makefile.inc
@@ -5,7 +5,7 @@ SECVAR_BACKEND_DIR = libstb/secvar/backend
 
 SUBDIRS += $(SECVAR_BACKEND_DIR)
 
-SECVAR_BACKEND_OBJS = edk2-compat.o edk2-compat-process.o edk2-compat-reset.o edk2-compat-static.o
+SECVAR_BACKEND_OBJS = edk2-compat.o edk2-compat-process.o edk2-compat-reset.o edk2-compat-static.o edk2-switchable.o
 SECVAR_BACKEND = $(SECVAR_BACKEND_DIR)/built-in.a
 
 $(SECVAR_BACKEND): $(SECVAR_BACKEND_OBJS:%=$(SECVAR_BACKEND_DIR)/%)
diff --git a/libstb/secvar/backend/edk2-switchable.c b/libstb/secvar/backend/edk2-switchable.c
new file mode 100644
index 00000000..f2883928
--- /dev/null
+++ b/libstb/secvar/backend/edk2-switchable.c
@@ -0,0 +1,46 @@
+#include <opal.h>
+#include <secvar.h>
+#include "../storage/secboot_tpm_switchable.h"
+#include "../secvar.h"
+
+static int switchable_pre_process(struct list_head *variable_bank,
+                                  struct list_head *update_bank)
+{
+        if (mode_value == USER_MODE)
+                return edk2_compatible_v1.pre_process(variable_bank, update_bank);
+        return edk2_compatible_v1_static.pre_process(variable_bank, update_bank);
+}
+
+
+static int switchable_process(struct list_head *variable_bank,
+                              struct list_head *update_bank)
+{
+        if (mode_value == USER_MODE)
+                return edk2_compatible_v1.process(variable_bank, update_bank);
+        return edk2_compatible_v1_static.process(variable_bank, update_bank);
+}
+
+static int switchable_post_process(struct list_head *variable_bank,
+                                   struct list_head *update_bank)
+{
+        if (mode_value == USER_MODE)
+                return edk2_compatible_v1.post_process(variable_bank, update_bank);
+        return edk2_compatible_v1_static.post_process(variable_bank, update_bank);
+}
+
+static int switchable_validate(struct secvar *var)
+{
+        if (mode_value == USER_MODE)
+                return edk2_compatible_v1.validate(var);
+        return edk2_compatible_v1_static.validate(var);
+};
+
+struct secvar_backend_driver edk2_switchable_driver = {
+	.pre_process = switchable_pre_process,
+	.process = switchable_process,
+	.post_process = switchable_post_process,
+	.validate = switchable_validate,
+        // TODO: perhaps this should also be a composite compatible?
+        // The interface isn't changing, but it might be useful to know if using a switchable backend
+	.compatible = "ibm,edk2-compat-v1",
+};
-- 
2.33.0