[PATCH v3 0/3] powerpc: Enabling IMA arch specific secure boot policies

[PATCH v3 0/3] powerpc: Enabling IMA arch specific secure boot policies

[Nayna Jain]

This patch set, previously named "powerpc: Enabling secure boot on powernv
systems - Part 1", is part of a series that implements secure boot on
PowerNV systems.

In order to verify the OS kernel on PowerNV, secure boot requires X.509
certificates trusted by the platform, the secure boot modes, and several
other pieces of information. These are stored in secure variables
controlled by OPAL, also known as OPAL secure variables.

The IMA architecture specific policy support on POWER is dependent on OPAL
runtime services to access secure variables. OPAL APIs in skiboot are
modified to define generic interface compatible to any backend. This
patchset is consequently updated to be compatible with new OPAL API
interface. This has cleaned up any EFIsms in the arch specific code.
Further, the ima arch specific policies are updated to be able to support
appended signatures. They also now use per policy template.

Exposing the OPAL secure variables to userspace will be posted as a
separate patch set, allowing the IMA architecture specific policy on POWER
to be upstreamed independently.

This patch set adds the following features:

1. Add support for OPAL Runtime API to access secure variables controlled
by OPAL.
2. Define IMA arch-specific policies based on the secure boot state and
mode of the system. On secure boot enabled PowerNV systems, the OS kernel
signature will be verified by IMA appraisal.

Pre-requisites for this patchset are:
1. OPAL APIs in Skiboot[1]
2. Appended signature support in IMA [2]
3. Per policy template support in IMA [3]

[1] https://patchwork.ozlabs.org/project/skiboot/list/?series=112868 
[2] https://patchwork.ozlabs.org/cover/1087361/. Updated version will be
posted soon
[3] Repo: https://kernel.googlesource.com/pub/scm/linux/kernel/git/zohar/linux-integrity
Branch: next-queued-testing. Commit: f241bb1f42aa95

----------------------------------------------------------------------------------

Original Cover Letter:

This patch set is part of a series that implements secure boot on PowerNV
systems.

In order to verify the OS kernel on PowerNV, secure boot requires X.509
certificates trusted by the platform, the secure boot modes, and several
other pieces of information. These are stored in secure variables
controlled by OPAL, also known as OPAL secure variables.

The IMA architecture specific policy support on Power is dependent on OPAL
runtime services to access secure variables. Instead of directly accessing
the OPAL runtime services, version 3 of this patch set relied upon the
EFI hooks. This version drops that dependency and calls the OPAL runtime
services directly. Skiboot OPAL APIs are due to be posted soon.

Exposing the OPAL secure variables to userspace will be posted as a
separate patch set, allowing the IMA architecture specific policy on Power
to be upstreamed independently.

This patch set adds the following features:

1. Add support for OPAL Runtime API to access secure variables controlled
by OPAL.
2. Define IMA arch-specific policies based on the secure boot state and
mode of the system. On secure boot enabled powernv systems, the OS kernel
signature will be verified by IMA appraisal.

[1] https://patchwork.kernel.org/cover/10882149/

Changelog:

v3:
* OPAL APIs in Patch 1 are updated to provide generic interface based on
key/keylen. This patchset updates kernel OPAL APIs to be compatible with
generic interface.
* Patch 2 is cleaned up to use new OPAL APIs. 
* Since OPAL can support different types of backend which can vary in the
variable interpretation, the Patch 2 is updated to add a check for the
backend version
* OPAL API now expects consumer to first check the supported backend version
before calling other secvar OPAL APIs. This check is now added in patch 2.
* IMA policies in Patch 3 is updated to specify appended signature and
per policy template.
* The patches now are free of any EFIisms.

v2:

* Removed Patch 1: powerpc/include: Override unneeded early ioremap
functions
* Updated Subject line and patch description of the Patch 1 of this series
* Removed dependency of OPAL_SECVAR on EFI, CPU_BIG_ENDIAN and UCS2_STRING
* Changed OPAL APIs from static to non-static. Added opal-secvar.h for the
same
* Removed EFI hooks from opal_secvar.c
* Removed opal_secvar_get_next(), opal_secvar_enqueue() and
opal_query_variable_info() function
* get_powerpc_sb_mode() in secboot.c now directly calls OPAL Runtime API
rather than via EFI hooks.
* Fixed log messages in get_powerpc_sb_mode() function.
* Added dependency for PPC_SECURE_BOOT on configs PPC64 and OPAL_SECVAR
* Replaced obj-$(CONFIG_IMA) with obj-$(CONFIG_PPC_SECURE_BOOT) in
arch/powerpc/kernel/Makefile

Claudio Carvalho (1):
  powerpc/powernv: Add OPAL API interface to get secureboot state

Nayna Jain (2):
  powerpc/powernv: detect the secure boot mode of the system
  powerpc: Add support to initialize ima policy rules

 arch/powerpc/Kconfig                         | 14 ++++
 arch/powerpc/include/asm/opal-api.h          |  4 +-
 arch/powerpc/include/asm/opal-secvar.h       | 23 ++++++
 arch/powerpc/include/asm/opal.h              |  6 ++
 arch/powerpc/include/asm/secboot.h           | 21 +++++
 arch/powerpc/kernel/Makefile                 |  1 +
 arch/powerpc/kernel/ima_arch.c               | 54 +++++++++++++
 arch/powerpc/platforms/powernv/Kconfig       |  6 ++
 arch/powerpc/platforms/powernv/Makefile      |  2 +
 arch/powerpc/platforms/powernv/opal-call.c   |  2 +
 arch/powerpc/platforms/powernv/opal-secvar.c | 85 ++++++++++++++++++++
 arch/powerpc/platforms/powernv/secboot.c     | 61 ++++++++++++++
 include/linux/ima.h                          |  3 +-
 13 files changed, 280 insertions(+), 2 deletions(-)
 create mode 100644 arch/powerpc/include/asm/opal-secvar.h
 create mode 100644 arch/powerpc/include/asm/secboot.h
 create mode 100644 arch/powerpc/kernel/ima_arch.c
 create mode 100644 arch/powerpc/platforms/powernv/opal-secvar.c
 create mode 100644 arch/powerpc/platforms/powernv/secboot.c

-- 
2.20.1

[PATCH v3 1/3] powerpc/powernv: Add OPAL API interface to get secureboot state

[Nayna Jain]

From: Claudio Carvalho <cclaudio@linux.ibm.com>

The X.509 certificates trusted by the platform and other information
required to secure boot the OS kernel are wrapped in secure variables,
which are controlled by OPAL.

This patch adds support to read OPAL secure variables through
OPAL_SECVAR_GET call. It returns the metadata and data for a given secure
variable based on the unique key.

Since OPAL can support different types of backend which can vary in the
variable interpretation, a new OPAL API call named OPAL_SECVAR_BACKEND, is
added to retrieve the supported backend version. This helps the consumer
to know how to interpret the variable.

This support can be enabled using CONFIG_OPAL_SECVAR

Signed-off-by: Claudio Carvalho <cclaudio@linux.ibm.com>
Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
---
This patch depends on a new OPAL call that is being added to skiboot.
The patch set that implements the new call has been posted to
https://patchwork.ozlabs.org/project/skiboot/list/?series=112868

 arch/powerpc/include/asm/opal-api.h          |  4 +-
 arch/powerpc/include/asm/opal-secvar.h       | 23 ++++++
 arch/powerpc/include/asm/opal.h              |  6 ++
 arch/powerpc/platforms/powernv/Kconfig       |  6 ++
 arch/powerpc/platforms/powernv/Makefile      |  1 +
 arch/powerpc/platforms/powernv/opal-call.c   |  2 +
 arch/powerpc/platforms/powernv/opal-secvar.c | 85 ++++++++++++++++++++
 7 files changed, 126 insertions(+), 1 deletion(-)
 create mode 100644 arch/powerpc/include/asm/opal-secvar.h
 create mode 100644 arch/powerpc/platforms/powernv/opal-secvar.c

diff --git a/arch/powerpc/include/asm/opal-api.h b/arch/powerpc/include/asm/opal-api.h
index e1577cfa7186..a505e669b4b6 100644
--- a/arch/powerpc/include/asm/opal-api.h
+++ b/arch/powerpc/include/asm/opal-api.h
@@ -212,7 +212,9 @@
 #define OPAL_HANDLE_HMI2			166
 #define	OPAL_NX_COPROC_INIT			167
 #define OPAL_XIVE_GET_VP_STATE			170
-#define OPAL_LAST				170
+#define OPAL_SECVAR_GET                         173
+#define OPAL_SECVAR_BACKEND                     177
+#define OPAL_LAST				177
 
 #define QUIESCE_HOLD			1 /* Spin all calls at entry */
 #define QUIESCE_REJECT			2 /* Fail all calls with OPAL_BUSY */
diff --git a/arch/powerpc/include/asm/opal-secvar.h b/arch/powerpc/include/asm/opal-secvar.h
new file mode 100644
index 000000000000..b677171a0368
--- /dev/null
+++ b/arch/powerpc/include/asm/opal-secvar.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * PowerNV definitions for secure variables OPAL API.
+ *
+ * Copyright (C) 2019 IBM Corporation
+ * Author: Claudio Carvalho <cclaudio@linux.ibm.com>
+ *
+ */
+#ifndef OPAL_SECVAR_H
+#define OPAL_SECVAR_H
+
+enum {
+	BACKEND_NONE = 0,
+	BACKEND_TC_COMPAT_V1,
+};
+
+extern int opal_get_variable(u8 *key, unsigned long ksize,
+			     u8 *metadata, unsigned long *mdsize,
+			     u8 *data, unsigned long *dsize);
+
+extern int opal_variable_version(unsigned long *backend);
+
+#endif
diff --git a/arch/powerpc/include/asm/opal.h b/arch/powerpc/include/asm/opal.h
index 4cc37e708bc7..57d2c2356eda 100644
--- a/arch/powerpc/include/asm/opal.h
+++ b/arch/powerpc/include/asm/opal.h
@@ -394,6 +394,12 @@ void opal_powercap_init(void);
 void opal_psr_init(void);
 void opal_sensor_groups_init(void);
 
+extern int opal_secvar_get(uint64_t k_key, uint64_t k_key_len,
+			   uint64_t k_metadata, uint64_t k_metadata_size,
+			   uint64_t k_data, uint64_t k_data_size);
+
+extern int opal_secvar_backend(uint64_t k_backend);
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_POWERPC_OPAL_H */
diff --git a/arch/powerpc/platforms/powernv/Kconfig b/arch/powerpc/platforms/powernv/Kconfig
index 850eee860cf2..65b060539b5c 100644
--- a/arch/powerpc/platforms/powernv/Kconfig
+++ b/arch/powerpc/platforms/powernv/Kconfig
@@ -47,3 +47,9 @@ config PPC_VAS
 	  VAS adapters are found in POWER9 based systems.
 
 	  If unsure, say N.
+
+config OPAL_SECVAR
+	bool "OPAL Secure Variables"
+	depends on PPC_POWERNV
+	help
+	  This enables the kernel to access OPAL secure variables.
diff --git a/arch/powerpc/platforms/powernv/Makefile b/arch/powerpc/platforms/powernv/Makefile
index da2e99efbd04..6651c742e530 100644
--- a/arch/powerpc/platforms/powernv/Makefile
+++ b/arch/powerpc/platforms/powernv/Makefile
@@ -16,3 +16,4 @@ obj-$(CONFIG_PERF_EVENTS) += opal-imc.o
 obj-$(CONFIG_PPC_MEMTRACE)	+= memtrace.o
 obj-$(CONFIG_PPC_VAS)	+= vas.o vas-window.o vas-debug.o
 obj-$(CONFIG_OCXL_BASE)	+= ocxl.o
+obj-$(CONFIG_OPAL_SECVAR) += opal-secvar.o
diff --git a/arch/powerpc/platforms/powernv/opal-call.c b/arch/powerpc/platforms/powernv/opal-call.c
index 36c8fa3647a2..0445980f294f 100644
--- a/arch/powerpc/platforms/powernv/opal-call.c
+++ b/arch/powerpc/platforms/powernv/opal-call.c
@@ -288,3 +288,5 @@ OPAL_CALL(opal_pci_set_pbcq_tunnel_bar,		OPAL_PCI_SET_PBCQ_TUNNEL_BAR);
 OPAL_CALL(opal_sensor_read_u64,			OPAL_SENSOR_READ_U64);
 OPAL_CALL(opal_sensor_group_enable,		OPAL_SENSOR_GROUP_ENABLE);
 OPAL_CALL(opal_nx_coproc_init,			OPAL_NX_COPROC_INIT);
+OPAL_CALL(opal_secvar_get,                      OPAL_SECVAR_GET);
+OPAL_CALL(opal_secvar_backend,                  OPAL_SECVAR_BACKEND);
diff --git a/arch/powerpc/platforms/powernv/opal-secvar.c b/arch/powerpc/platforms/powernv/opal-secvar.c
new file mode 100644
index 000000000000..dba441dd5af1
--- /dev/null
+++ b/arch/powerpc/platforms/powernv/opal-secvar.c
@@ -0,0 +1,85 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * PowerNV code for secure variables
+ *
+ * Copyright (C) 2019 IBM Corporation
+ * Author: Claudio Carvalho <cclaudio@linux.ibm.com>
+ *
+ */
+
+/*
+ * The opal wrappers in this file treat the @name, @vendor, and @data
+ * parameters as little endian blobs.
+ * @name is a ucs2 string
+ * @vendor is the vendor GUID. It is converted to LE in the kernel
+ * @data variable data, which layout may be different for each variable
+ */
+
+#define pr_fmt(fmt) "secvar: "fmt
+
+#include <linux/types.h>
+#include <asm/opal.h>
+#include <asm/opal-secvar.h>
+
+static bool is_opal_secvar_supported(void)
+{
+	static bool opal_secvar_supported;
+	static bool initialized;
+
+	if (initialized)
+		return opal_secvar_supported;
+
+	if (!opal_check_token(OPAL_SECVAR_GET)
+	    || !opal_check_token(OPAL_SECVAR_BACKEND)) {
+		pr_err("OPAL doesn't support secure variables\n");
+		opal_secvar_supported = false;
+	} else {
+		opal_secvar_supported = true;
+	}
+
+	initialized = true;
+
+	return opal_secvar_supported;
+}
+
+int opal_get_variable(u8 *key, unsigned long ksize, u8 *metadata,
+		      unsigned long *mdsize, u8 *data, unsigned long *dsize)
+{
+	int rc;
+
+	if (!is_opal_secvar_supported())
+		return OPAL_UNSUPPORTED;
+
+	if (mdsize)
+		*mdsize = cpu_to_be64(*mdsize);
+	if (dsize)
+		*dsize = cpu_to_be64(*dsize);
+
+	rc = opal_secvar_get(__pa(key), ksize, __pa(metadata), __pa(mdsize),
+			     __pa(data), __pa(dsize));
+
+	if (mdsize)
+		*mdsize = be64_to_cpu(*mdsize);
+	if (dsize)
+		*dsize = be64_to_cpu(*dsize);
+
+	return rc;
+}
+
+int opal_variable_version(unsigned long *backend)
+{
+	int rc;
+
+	if (!is_opal_secvar_supported())
+		return OPAL_UNSUPPORTED;
+
+	if (backend)
+		*backend = cpu_to_be64(*backend);
+
+	rc = opal_secvar_backend(__pa(backend));
+
+	if (backend)
+		*backend = be64_to_cpu(*backend);
+
+	return rc;
+}
-- 
2.20.1

[PATCH v3 2/3] powerpc/powernv: detect the secure boot mode of the system

[Nayna Jain]

PowerNV secure boot defines different IMA policies based on the secure
boot state of the system.

This patch defines a function to detect the secure boot state of the
system.

Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
---
 arch/powerpc/include/asm/secboot.h       | 21 ++++++++
 arch/powerpc/platforms/powernv/Makefile  |  3 +-
 arch/powerpc/platforms/powernv/secboot.c | 61 ++++++++++++++++++++++++
 3 files changed, 84 insertions(+), 1 deletion(-)
 create mode 100644 arch/powerpc/include/asm/secboot.h
 create mode 100644 arch/powerpc/platforms/powernv/secboot.c

diff --git a/arch/powerpc/include/asm/secboot.h b/arch/powerpc/include/asm/secboot.h
new file mode 100644
index 000000000000..1904fb4a3352
--- /dev/null
+++ b/arch/powerpc/include/asm/secboot.h
@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * PowerPC secure boot definitions
+ *
+ * Copyright (C) 2019 IBM Corporation
+ * Author: Nayna Jain <nayna@linux.ibm.com>
+ *
+ */
+#ifndef POWERPC_SECBOOT_H
+#define POWERPC_SECBOOT_H
+
+#if defined(CONFIG_OPAL_SECVAR)
+extern bool get_powerpc_sb_mode(void);
+#else
+static inline bool get_powerpc_sb_mode(void)
+{
+	return false;
+}
+#endif
+
+#endif
diff --git a/arch/powerpc/platforms/powernv/Makefile b/arch/powerpc/platforms/powernv/Makefile
index 6651c742e530..74705a3fc474 100644
--- a/arch/powerpc/platforms/powernv/Makefile
+++ b/arch/powerpc/platforms/powernv/Makefile
@@ -4,6 +4,7 @@ obj-y			+= idle.o opal-rtc.o opal-nvram.o opal-lpc.o opal-flash.o
 obj-y			+= rng.o opal-elog.o opal-dump.o opal-sysparam.o opal-sensor.o
 obj-y			+= opal-msglog.o opal-hmi.o opal-power.o opal-irqchip.o
 obj-y			+= opal-kmsg.o opal-powercap.o opal-psr.o opal-sensor-groups.o
+obj-y			+= secboot.o
 
 obj-$(CONFIG_SMP)	+= smp.o subcore.o subcore-asm.o
 obj-$(CONFIG_PCI)	+= pci.o pci-ioda.o npu-dma.o pci-ioda-tce.o
@@ -16,4 +17,4 @@ obj-$(CONFIG_PERF_EVENTS) += opal-imc.o
 obj-$(CONFIG_PPC_MEMTRACE)	+= memtrace.o
 obj-$(CONFIG_PPC_VAS)	+= vas.o vas-window.o vas-debug.o
 obj-$(CONFIG_OCXL_BASE)	+= ocxl.o
-obj-$(CONFIG_OPAL_SECVAR) += opal-secvar.o
+obj-$(CONFIG_OPAL_SECVAR) += opal-secvar.o secboot.o
diff --git a/arch/powerpc/platforms/powernv/secboot.c b/arch/powerpc/platforms/powernv/secboot.c
new file mode 100644
index 000000000000..9199e520ebed
--- /dev/null
+++ b/arch/powerpc/platforms/powernv/secboot.c
@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2019 IBM Corporation
+ * Author: Nayna Jain <nayna@linux.ibm.com>
+ *
+ * secboot.c
+ *      - util function to get powerpc secboot state
+ */
+#include <linux/uuid.h>
+#include <asm/opal.h>
+#include <asm/secboot.h>
+#include <asm/opal-secvar.h>
+
+bool get_powerpc_sb_mode(void)
+{
+	u8 secure_boot_name[] = "SecureBoot";
+	u8 setup_mode_name[] = "SetupMode";
+	u8 secboot, setupmode;
+	unsigned long size = sizeof(secboot);
+	int status;
+	unsigned long version;
+
+	status = opal_variable_version(&version);
+	if ((status != OPAL_SUCCESS) || (version != BACKEND_TC_COMPAT_V1)) {
+		pr_info("secboot: error retrieving compatible backend\n");
+		return false;
+	}
+
+	status = opal_get_variable(secure_boot_name, sizeof(secure_boot_name),
+				   NULL, NULL, &secboot, &size);
+
+	/*
+	 * For now assume all failures reading the SecureBoot variable implies
+	 * secure boot is not enabled. Later differentiate failure types.
+	 */
+	if (status != OPAL_SUCCESS) {
+		secboot = 0;
+		setupmode = 0;
+		goto out;
+	}
+
+	size = sizeof(setupmode);
+	status = opal_get_variable(setup_mode_name, sizeof(setup_mode_name),
+				   NULL, NULL,  &setupmode, &size);
+
+	/*
+	 * Failure to read the SetupMode variable does not prevent
+	 * secure boot mode
+	 */
+	if (status != OPAL_SUCCESS)
+		setupmode = 0;
+
+out:
+	if ((secboot == 0) || (setupmode == 1)) {
+		pr_info("secboot: secureboot mode disabled\n");
+		return false;
+	}
+
+	pr_info("secboot: secureboot mode enabled\n");
+	return true;
+}
-- 
2.20.1

[PATCH v3 3/3] powerpc: Add support to initialize ima policy rules

[Nayna Jain]

PowerNV secure boot relies on the kernel IMA security subsystem to
perform the OS kernel image signature verification. Since each secure
boot mode has different IMA policy requirements, dynamic definition of
the policy rules based on the runtime secure boot mode of the system is
required. On systems that support secure boot, but have it disabled,
only measurement policy rules of the kernel image and modules are
defined.

This patch defines the arch-specific implementation to retrieve the
secure boot mode of the system and accordingly configures the IMA policy
rules.

This patch provides arch-specific IMA policies if PPC_SECURE_BOOT
config is enabled.

Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
---
 arch/powerpc/Kconfig           | 14 +++++++++
 arch/powerpc/kernel/Makefile   |  1 +
 arch/powerpc/kernel/ima_arch.c | 54 ++++++++++++++++++++++++++++++++++
 include/linux/ima.h            |  3 +-
 4 files changed, 71 insertions(+), 1 deletion(-)
 create mode 100644 arch/powerpc/kernel/ima_arch.c

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 8c1c636308c8..9de77bb14f54 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -902,6 +902,20 @@ config PPC_MEM_KEYS
 
 	  If unsure, say y.
 
+config PPC_SECURE_BOOT
+	prompt "Enable PowerPC Secure Boot"
+	bool
+	default n
+	depends on PPC64
+	depends on OPAL_SECVAR
+	depends on IMA
+	depends on IMA_ARCH_POLICY
+	help
+	  Linux on POWER with firmware secure boot enabled needs to define
+	  security policies to extend secure boot to the OS.This config
+	  allows user to enable OS Secure Boot on PowerPC systems that
+	  have firmware secure boot support.
+
 endmenu
 
 config ISA_DMA_API
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index 0ea6c4aa3a20..75c929b41341 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -131,6 +131,7 @@ ifdef CONFIG_IMA
 obj-y				+= ima_kexec.o
 endif
 endif
+obj-$(CONFIG_PPC_SECURE_BOOT)	+= ima_arch.o
 
 obj-$(CONFIG_AUDIT)		+= audit.o
 obj64-$(CONFIG_AUDIT)		+= compat_audit.o
diff --git a/arch/powerpc/kernel/ima_arch.c b/arch/powerpc/kernel/ima_arch.c
new file mode 100644
index 000000000000..1767bf6e6550
--- /dev/null
+++ b/arch/powerpc/kernel/ima_arch.c
@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2019 IBM Corporation
+ * Author: Nayna Jain <nayna@linux.ibm.com>
+ *
+ * ima_arch.c
+ *      - initialize ima policies for PowerPC Secure Boot
+ */
+
+#include <linux/ima.h>
+#include <asm/secboot.h>
+
+bool arch_ima_get_secureboot(void)
+{
+	bool sb_mode;
+
+	sb_mode = get_powerpc_sb_mode();
+	if (sb_mode)
+		return true;
+	else
+		return false;
+}
+
+/*
+ * File signature verification is not needed, include only measurements
+ */
+static const char *const default_arch_rules[] = {
+	"measure func=KEXEC_KERNEL_CHECK template=ima-modsig",
+	"measure func=MODULE_CHECK template=ima-modsig",
+	NULL
+};
+
+/* Both file signature verification and measurements are needed */
+static const char *const sb_arch_rules[] = {
+	"measure func=KEXEC_KERNEL_CHECK template=ima-modsig",
+	"measure func=MODULE_CHECK template=ima-modsig",
+	"appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig|modsig template=ima-modsig",
+#if !IS_ENABLED(CONFIG_MODULE_SIG)
+	"appraise func=MODULE_CHECK appraise_type=imasig|modsig template=ima-modsig",
+#endif
+	NULL
+};
+
+/*
+ * On PowerPC, file measurements are to be added to the IMA measurement list
+ * irrespective of the secure boot state of the system. Signature verification
+ * is conditionally enabled based on the secure boot state.
+ */
+const char *const *arch_get_ima_policy(void)
+{
+	if (IS_ENABLED(CONFIG_IMA_ARCH_POLICY) && arch_ima_get_secureboot())
+		return sb_arch_rules;
+	return default_arch_rules;
+}
diff --git a/include/linux/ima.h b/include/linux/ima.h
index fd9f7cf4cdf5..a01df076ecae 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -31,7 +31,8 @@ extern void ima_post_path_mknod(struct dentry *dentry);
 extern void ima_add_kexec_buffer(struct kimage *image);
 #endif
 
-#if (defined(CONFIG_X86) && defined(CONFIG_EFI)) || defined(CONFIG_S390)
+#if (defined(CONFIG_X86) && defined(CONFIG_EFI)) || defined(CONFIG_S390) \
+	|| defined(CONFIG_PPC_SECURE_BOOT)
 extern bool arch_ima_get_secureboot(void);
 extern const char * const *arch_get_ima_policy(void);
 #else
-- 
2.20.1

Re: [PATCH v3 3/3] powerpc: Add support to initialize ima policy rules

[Satheesh Rajendran]

On Mon, Jun 10, 2019 at 04:33:57PM -0400, Nayna Jain wrote:
> PowerNV secure boot relies on the kernel IMA security subsystem to
> perform the OS kernel image signature verification. Since each secure
> boot mode has different IMA policy requirements, dynamic definition of
> the policy rules based on the runtime secure boot mode of the system is
> required. On systems that support secure boot, but have it disabled,
> only measurement policy rules of the kernel image and modules are
> defined.
> 
> This patch defines the arch-specific implementation to retrieve the
> secure boot mode of the system and accordingly configures the IMA policy
> rules.
> 
> This patch provides arch-specific IMA policies if PPC_SECURE_BOOT
> config is enabled.
> 
> Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
> ---
>  arch/powerpc/Kconfig           | 14 +++++++++
>  arch/powerpc/kernel/Makefile   |  1 +
>  arch/powerpc/kernel/ima_arch.c | 54 ++++++++++++++++++++++++++++++++++
>  include/linux/ima.h            |  3 +-
>  4 files changed, 71 insertions(+), 1 deletion(-)
>  create mode 100644 arch/powerpc/kernel/ima_arch.c

Hi,

This series failed to build against linuxppc/merge tree with `ppc64le_defconfig`,

arch/powerpc/platforms/powernv/secboot.c:14:6: error: redefinition of 'get_powerpc_sb_mode'
   14 | bool get_powerpc_sb_mode(void)
      |      ^~~~~~~~~~~~~~~~~~~
In file included from arch/powerpc/platforms/powernv/secboot.c:11:
./arch/powerpc/include/asm/secboot.h:15:20: note: previous definition of 'get_powerpc_sb_mode' was here
   15 | static inline bool get_powerpc_sb_mode(void)
      |                    ^~~~~~~~~~~~~~~~~~~
make[3]: *** [scripts/Makefile.build:278: arch/powerpc/platforms/powernv/secboot.o] Error 1
make[3]: *** Waiting for unfinished jobs....
make[2]: *** [scripts/Makefile.build:489: arch/powerpc/platforms/powernv] Error 2
make[1]: *** [scripts/Makefile.build:489: arch/powerpc/platforms] Error 2
make: *** [Makefile:1071: arch/powerpc] Error 2
make: *** Waiting for unfinished jobs....

Regards,
-Satheesh

> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 8c1c636308c8..9de77bb14f54 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -902,6 +902,20 @@ config PPC_MEM_KEYS
> 
>  	  If unsure, say y.
> 
> +config PPC_SECURE_BOOT
> +	prompt "Enable PowerPC Secure Boot"
> +	bool
> +	default n
> +	depends on PPC64
> +	depends on OPAL_SECVAR
> +	depends on IMA
> +	depends on IMA_ARCH_POLICY
> +	help
> +	  Linux on POWER with firmware secure boot enabled needs to define
> +	  security policies to extend secure boot to the OS.This config
> +	  allows user to enable OS Secure Boot on PowerPC systems that
> +	  have firmware secure boot support.
> +
>  endmenu
> 
>  config ISA_DMA_API
> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> index 0ea6c4aa3a20..75c929b41341 100644
> --- a/arch/powerpc/kernel/Makefile
> +++ b/arch/powerpc/kernel/Makefile
> @@ -131,6 +131,7 @@ ifdef CONFIG_IMA
>  obj-y				+= ima_kexec.o
>  endif
>  endif
> +obj-$(CONFIG_PPC_SECURE_BOOT)	+= ima_arch.o
> 
>  obj-$(CONFIG_AUDIT)		+= audit.o
>  obj64-$(CONFIG_AUDIT)		+= compat_audit.o
> diff --git a/arch/powerpc/kernel/ima_arch.c b/arch/powerpc/kernel/ima_arch.c
> new file mode 100644
> index 000000000000..1767bf6e6550
> --- /dev/null
> +++ b/arch/powerpc/kernel/ima_arch.c
> @@ -0,0 +1,54 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2019 IBM Corporation
> + * Author: Nayna Jain <nayna@linux.ibm.com>
> + *
> + * ima_arch.c
> + *      - initialize ima policies for PowerPC Secure Boot
> + */
> +
> +#include <linux/ima.h>
> +#include <asm/secboot.h>
> +
> +bool arch_ima_get_secureboot(void)
> +{
> +	bool sb_mode;
> +
> +	sb_mode = get_powerpc_sb_mode();
> +	if (sb_mode)
> +		return true;
> +	else
> +		return false;
> +}
> +
> +/*
> + * File signature verification is not needed, include only measurements
> + */
> +static const char *const default_arch_rules[] = {
> +	"measure func=KEXEC_KERNEL_CHECK template=ima-modsig",
> +	"measure func=MODULE_CHECK template=ima-modsig",
> +	NULL
> +};
> +
> +/* Both file signature verification and measurements are needed */
> +static const char *const sb_arch_rules[] = {
> +	"measure func=KEXEC_KERNEL_CHECK template=ima-modsig",
> +	"measure func=MODULE_CHECK template=ima-modsig",
> +	"appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig|modsig template=ima-modsig",
> +#if !IS_ENABLED(CONFIG_MODULE_SIG)
> +	"appraise func=MODULE_CHECK appraise_type=imasig|modsig template=ima-modsig",
> +#endif
> +	NULL
> +};
> +
> +/*
> + * On PowerPC, file measurements are to be added to the IMA measurement list
> + * irrespective of the secure boot state of the system. Signature verification
> + * is conditionally enabled based on the secure boot state.
> + */
> +const char *const *arch_get_ima_policy(void)
> +{
> +	if (IS_ENABLED(CONFIG_IMA_ARCH_POLICY) && arch_ima_get_secureboot())
> +		return sb_arch_rules;
> +	return default_arch_rules;
> +}
> diff --git a/include/linux/ima.h b/include/linux/ima.h
> index fd9f7cf4cdf5..a01df076ecae 100644
> --- a/include/linux/ima.h
> +++ b/include/linux/ima.h
> @@ -31,7 +31,8 @@ extern void ima_post_path_mknod(struct dentry *dentry);
>  extern void ima_add_kexec_buffer(struct kimage *image);
>  #endif
> 
> -#if (defined(CONFIG_X86) && defined(CONFIG_EFI)) || defined(CONFIG_S390)
> +#if (defined(CONFIG_X86) && defined(CONFIG_EFI)) || defined(CONFIG_S390) \
> +	|| defined(CONFIG_PPC_SECURE_BOOT)
>  extern bool arch_ima_get_secureboot(void);
>  extern const char * const *arch_get_ima_policy(void);
>  #else
> -- 
> 2.20.1
> 

Re: [PATCH v3 3/3] powerpc: Add support to initialize ima policy rules

[Nayna]

On 06/11/2019 01:19 AM, Satheesh Rajendran wrote:
> On Mon, Jun 10, 2019 at 04:33:57PM -0400, Nayna Jain wrote:
>> PowerNV secure boot relies on the kernel IMA security subsystem to
>> perform the OS kernel image signature verification. Since each secure
>> boot mode has different IMA policy requirements, dynamic definition of
>> the policy rules based on the runtime secure boot mode of the system is
>> required. On systems that support secure boot, but have it disabled,
>> only measurement policy rules of the kernel image and modules are
>> defined.
>>
>> This patch defines the arch-specific implementation to retrieve the
>> secure boot mode of the system and accordingly configures the IMA policy
>> rules.
>>
>> This patch provides arch-specific IMA policies if PPC_SECURE_BOOT
>> config is enabled.
>>
>> Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
>> ---
>>   arch/powerpc/Kconfig           | 14 +++++++++
>>   arch/powerpc/kernel/Makefile   |  1 +
>>   arch/powerpc/kernel/ima_arch.c | 54 ++++++++++++++++++++++++++++++++++
>>   include/linux/ima.h            |  3 +-
>>   4 files changed, 71 insertions(+), 1 deletion(-)
>>   create mode 100644 arch/powerpc/kernel/ima_arch.c
> Hi,
>
> This series failed to build against linuxppc/merge tree with `ppc64le_defconfig`,
>
> arch/powerpc/platforms/powernv/secboot.c:14:6: error: redefinition of 'get_powerpc_sb_mode'
>     14 | bool get_powerpc_sb_mode(void)
>        |      ^~~~~~~~~~~~~~~~~~~
> In file included from arch/powerpc/platforms/powernv/secboot.c:11:
> ./arch/powerpc/include/asm/secboot.h:15:20: note: previous definition of 'get_powerpc_sb_mode' was here
>     15 | static inline bool get_powerpc_sb_mode(void)
>        |                    ^~~~~~~~~~~~~~~~~~~
> make[3]: *** [scripts/Makefile.build:278: arch/powerpc/platforms/powernv/secboot.o] Error 1
> make[3]: *** Waiting for unfinished jobs....
> make[2]: *** [scripts/Makefile.build:489: arch/powerpc/platforms/powernv] Error 2
> make[1]: *** [scripts/Makefile.build:489: arch/powerpc/platforms] Error 2
> make: *** [Makefile:1071: arch/powerpc] Error 2
> make: *** Waiting for unfinished jobs....


Thanks for reporting. I have fixed it and reposted as v4.

Please retry.

Thanks & Regards,
      - Nayna

Re: [PATCH v3 1/3] powerpc/powernv: Add OPAL API interface to get secureboot state

[Daniel Axtens]

Nayna Jain <nayna@linux.ibm.com> writes:

> From: Claudio Carvalho <cclaudio@linux.ibm.com>
>
> The X.509 certificates trusted by the platform and other information
> required to secure boot the OS kernel are wrapped in secure variables,
> which are controlled by OPAL.
>
> This patch adds support to read OPAL secure variables through
> OPAL_SECVAR_GET call. It returns the metadata and data for a given secure
> variable based on the unique key.
>
> Since OPAL can support different types of backend which can vary in the
> variable interpretation, a new OPAL API call named OPAL_SECVAR_BACKEND, is
> added to retrieve the supported backend version. This helps the consumer
> to know how to interpret the variable.
>

(Firstly, apologies that I haven't got around to asking about this yet!)

Are pluggable/versioned backend a good idea?

There are a few things that worry me about the idea:

 - It adds complexity in crypto (or crypto-adjacent) code, and that
   increases the likelihood that we'll accidentally add a bug with bad
   consequences.

 - Under what circumstances would would we change the kernel-visible
   behaviour of skiboot? Are we expecting to change the behaviour,
   content or names of the variables in future? Otherwise the only
   relevant change I can think of is a change to hardware platforms, and
   I'm not sure how a change in hardware would lead to change in
   behaviour in the kernel. Wouldn't Skiboot hide h/w differences?

 - If we are worried about a long-term-future change to how secure-boot
   works, would it be better to just add more get/set calls to opal at
   the point at which we actually implement the new system?
   
 - UEFI added EFI_VARIABLE_AUTHENTICATION_3 in a way that - as far
   as I know - didn't break backwards compatibility. Is there a reason
   we cannot add features that way instead? (It also dropped v1 of the
   authentication header.)
   
 - What is the correct fallback behaviour if a kernel receives a result
   that it does not expect? If a kernel expecting BackendV1 is instead
   informed that it is running on BackendV2, then the cannot access the
   secure variable at all, so it cannot load keys that are potentially
   required to successfully boot (e.g. to validate the module for
   network card or graphics!)

Kind regards,
Daniel

> This support can be enabled using CONFIG_OPAL_SECVAR
>
> Signed-off-by: Claudio Carvalho <cclaudio@linux.ibm.com>
> Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
> ---
> This patch depends on a new OPAL call that is being added to skiboot.
> The patch set that implements the new call has been posted to
> https://patchwork.ozlabs.org/project/skiboot/list/?series=112868
>
>  arch/powerpc/include/asm/opal-api.h          |  4 +-
>  arch/powerpc/include/asm/opal-secvar.h       | 23 ++++++
>  arch/powerpc/include/asm/opal.h              |  6 ++
>  arch/powerpc/platforms/powernv/Kconfig       |  6 ++
>  arch/powerpc/platforms/powernv/Makefile      |  1 +
>  arch/powerpc/platforms/powernv/opal-call.c   |  2 +
>  arch/powerpc/platforms/powernv/opal-secvar.c | 85 ++++++++++++++++++++
>  7 files changed, 126 insertions(+), 1 deletion(-)
>  create mode 100644 arch/powerpc/include/asm/opal-secvar.h
>  create mode 100644 arch/powerpc/platforms/powernv/opal-secvar.c
>
> diff --git a/arch/powerpc/include/asm/opal-api.h b/arch/powerpc/include/asm/opal-api.h
> index e1577cfa7186..a505e669b4b6 100644
> --- a/arch/powerpc/include/asm/opal-api.h
> +++ b/arch/powerpc/include/asm/opal-api.h
> @@ -212,7 +212,9 @@
>  #define OPAL_HANDLE_HMI2			166
>  #define	OPAL_NX_COPROC_INIT			167
>  #define OPAL_XIVE_GET_VP_STATE			170
> -#define OPAL_LAST				170
> +#define OPAL_SECVAR_GET                         173
> +#define OPAL_SECVAR_BACKEND                     177
> +#define OPAL_LAST				177
>  
>  #define QUIESCE_HOLD			1 /* Spin all calls at entry */
>  #define QUIESCE_REJECT			2 /* Fail all calls with OPAL_BUSY */
> diff --git a/arch/powerpc/include/asm/opal-secvar.h b/arch/powerpc/include/asm/opal-secvar.h
> new file mode 100644
> index 000000000000..b677171a0368
> --- /dev/null
> +++ b/arch/powerpc/include/asm/opal-secvar.h
> @@ -0,0 +1,23 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * PowerNV definitions for secure variables OPAL API.
> + *
> + * Copyright (C) 2019 IBM Corporation
> + * Author: Claudio Carvalho <cclaudio@linux.ibm.com>
> + *
> + */
> +#ifndef OPAL_SECVAR_H
> +#define OPAL_SECVAR_H
> +
> +enum {
> +	BACKEND_NONE = 0,
> +	BACKEND_TC_COMPAT_V1,
> +};
> +
> +extern int opal_get_variable(u8 *key, unsigned long ksize,
> +			     u8 *metadata, unsigned long *mdsize,
> +			     u8 *data, unsigned long *dsize);
> +
> +extern int opal_variable_version(unsigned long *backend);
> +
> +#endif
> diff --git a/arch/powerpc/include/asm/opal.h b/arch/powerpc/include/asm/opal.h
> index 4cc37e708bc7..57d2c2356eda 100644
> --- a/arch/powerpc/include/asm/opal.h
> +++ b/arch/powerpc/include/asm/opal.h
> @@ -394,6 +394,12 @@ void opal_powercap_init(void);
>  void opal_psr_init(void);
>  void opal_sensor_groups_init(void);
>  
> +extern int opal_secvar_get(uint64_t k_key, uint64_t k_key_len,
> +			   uint64_t k_metadata, uint64_t k_metadata_size,
> +			   uint64_t k_data, uint64_t k_data_size);
> +
> +extern int opal_secvar_backend(uint64_t k_backend);
> +
>  #endif /* __ASSEMBLY__ */
>  
>  #endif /* _ASM_POWERPC_OPAL_H */
> diff --git a/arch/powerpc/platforms/powernv/Kconfig b/arch/powerpc/platforms/powernv/Kconfig
> index 850eee860cf2..65b060539b5c 100644
> --- a/arch/powerpc/platforms/powernv/Kconfig
> +++ b/arch/powerpc/platforms/powernv/Kconfig
> @@ -47,3 +47,9 @@ config PPC_VAS
>  	  VAS adapters are found in POWER9 based systems.
>  
>  	  If unsure, say N.
> +
> +config OPAL_SECVAR
> +	bool "OPAL Secure Variables"
> +	depends on PPC_POWERNV
> +	help
> +	  This enables the kernel to access OPAL secure variables.
> diff --git a/arch/powerpc/platforms/powernv/Makefile b/arch/powerpc/platforms/powernv/Makefile
> index da2e99efbd04..6651c742e530 100644
> --- a/arch/powerpc/platforms/powernv/Makefile
> +++ b/arch/powerpc/platforms/powernv/Makefile
> @@ -16,3 +16,4 @@ obj-$(CONFIG_PERF_EVENTS) += opal-imc.o
>  obj-$(CONFIG_PPC_MEMTRACE)	+= memtrace.o
>  obj-$(CONFIG_PPC_VAS)	+= vas.o vas-window.o vas-debug.o
>  obj-$(CONFIG_OCXL_BASE)	+= ocxl.o
> +obj-$(CONFIG_OPAL_SECVAR) += opal-secvar.o
> diff --git a/arch/powerpc/platforms/powernv/opal-call.c b/arch/powerpc/platforms/powernv/opal-call.c
> index 36c8fa3647a2..0445980f294f 100644
> --- a/arch/powerpc/platforms/powernv/opal-call.c
> +++ b/arch/powerpc/platforms/powernv/opal-call.c
> @@ -288,3 +288,5 @@ OPAL_CALL(opal_pci_set_pbcq_tunnel_bar,		OPAL_PCI_SET_PBCQ_TUNNEL_BAR);
>  OPAL_CALL(opal_sensor_read_u64,			OPAL_SENSOR_READ_U64);
>  OPAL_CALL(opal_sensor_group_enable,		OPAL_SENSOR_GROUP_ENABLE);
>  OPAL_CALL(opal_nx_coproc_init,			OPAL_NX_COPROC_INIT);
> +OPAL_CALL(opal_secvar_get,                      OPAL_SECVAR_GET);
> +OPAL_CALL(opal_secvar_backend,                  OPAL_SECVAR_BACKEND);
> diff --git a/arch/powerpc/platforms/powernv/opal-secvar.c b/arch/powerpc/platforms/powernv/opal-secvar.c
> new file mode 100644
> index 000000000000..dba441dd5af1
> --- /dev/null
> +++ b/arch/powerpc/platforms/powernv/opal-secvar.c
> @@ -0,0 +1,85 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * PowerNV code for secure variables
> + *
> + * Copyright (C) 2019 IBM Corporation
> + * Author: Claudio Carvalho <cclaudio@linux.ibm.com>
> + *
> + */
> +
> +/*
> + * The opal wrappers in this file treat the @name, @vendor, and @data
> + * parameters as little endian blobs.
> + * @name is a ucs2 string
> + * @vendor is the vendor GUID. It is converted to LE in the kernel
> + * @data variable data, which layout may be different for each variable
> + */
> +
> +#define pr_fmt(fmt) "secvar: "fmt
> +
> +#include <linux/types.h>
> +#include <asm/opal.h>
> +#include <asm/opal-secvar.h>
> +
> +static bool is_opal_secvar_supported(void)
> +{
> +	static bool opal_secvar_supported;
> +	static bool initialized;
> +
> +	if (initialized)
> +		return opal_secvar_supported;
> +
> +	if (!opal_check_token(OPAL_SECVAR_GET)
> +	    || !opal_check_token(OPAL_SECVAR_BACKEND)) {
> +		pr_err("OPAL doesn't support secure variables\n");
> +		opal_secvar_supported = false;
> +	} else {
> +		opal_secvar_supported = true;
> +	}
> +
> +	initialized = true;
> +
> +	return opal_secvar_supported;
> +}
> +
> +int opal_get_variable(u8 *key, unsigned long ksize, u8 *metadata,
> +		      unsigned long *mdsize, u8 *data, unsigned long *dsize)
> +{
> +	int rc;
> +
> +	if (!is_opal_secvar_supported())
> +		return OPAL_UNSUPPORTED;
> +
> +	if (mdsize)
> +		*mdsize = cpu_to_be64(*mdsize);
> +	if (dsize)
> +		*dsize = cpu_to_be64(*dsize);
> +
> +	rc = opal_secvar_get(__pa(key), ksize, __pa(metadata), __pa(mdsize),
> +			     __pa(data), __pa(dsize));
> +
> +	if (mdsize)
> +		*mdsize = be64_to_cpu(*mdsize);
> +	if (dsize)
> +		*dsize = be64_to_cpu(*dsize);
> +
> +	return rc;
> +}
> +
> +int opal_variable_version(unsigned long *backend)
> +{
> +	int rc;
> +
> +	if (!is_opal_secvar_supported())
> +		return OPAL_UNSUPPORTED;
> +
> +	if (backend)
> +		*backend = cpu_to_be64(*backend);
> +
> +	rc = opal_secvar_backend(__pa(backend));
> +
> +	if (backend)
> +		*backend = be64_to_cpu(*backend);
> +
> +	return rc;
> +}
> -- 
> 2.20.1

Re: [PATCH v3 1/3] powerpc/powernv: Add OPAL API interface to get secureboot state

[Daniel Axtens]

Hi Nayna,

>>> Since OPAL can support different types of backend which can vary in the
>>> variable interpretation, a new OPAL API call named OPAL_SECVAR_BACKEND, is
>>> added to retrieve the supported backend version. This helps the consumer
>>> to know how to interpret the variable.
>>>
>> (Firstly, apologies that I haven't got around to asking about this yet!)
>>
>> Are pluggable/versioned backend a good idea?
>>
>> There are a few things that worry me about the idea:
>>
>>   - It adds complexity in crypto (or crypto-adjacent) code, and that
>>     increases the likelihood that we'll accidentally add a bug with bad
>>     consequences.
>
> Sorry, I think I am not clear on what exactly you mean here.Can you 
> please elaborate or give specifics ?

Cryptosystems with greater flexibility can have new kinds of
vulnerabilities arise from the greater complexity. The first sort of
thing that comes to mind is a downgrade attack like from TLS. I think
you're protected from this because the mode cannot be negotiatied at run
time, but in general it's security sensitive code so I'd like it to be
as simple as possible.

>>   - If we are worried about a long-term-future change to how secure-boot
>>     works, would it be better to just add more get/set calls to opal at
>>     the point at which we actually implement the new system?
>
> The intention is to avoid to re-implement the key/value interface for 
> each scheme. Do you mean to deprecate the old APIs and add new APIs with 
> every scheme ?

Yes, because I expect the scheme would change very, very rarely.

>>   - Under what circumstances would would we change the kernel-visible
>>     behaviour of skiboot? Are we expecting to change the behaviour,
>>     content or names of the variables in future? Otherwise the only
>>     relevant change I can think of is a change to hardware platforms, and
>>     I'm not sure how a change in hardware would lead to change in
>>     behaviour in the kernel. Wouldn't Skiboot hide h/w differences?
>
> Backends are intended to be an agreement for firmware, kernel and 
> userspace on what the format of variables are, what variables should be 
> expected, how they should be signed, etc. Though we don't expect it to 
> happen very often, we want to anticipate possible changes in the 
> firmware which may affect the kernel such as new features, support of 
> new authentication mechanisms, addition of new variables. Corresponding 
> skiboot patches are on - 
> https://lists.ozlabs.org/pipermail/skiboot/2019-June/014641.html

I still feel like this is holding onto ongoing complexity for very
little gain, but perhaps this is because I can't picture a specific
change that would actually require a wholesale change to the scheme.

You mention new features, support for new authentication mechanisms, and
addition of new variables.

 - New features is a bit too generic to answer specifically. In general
   I accept that there exists some new feature that would be
   sufficiently backwards-incompatible as to require a new version. I
   just can't think of one off the top of my head and so I'm not
   convinced it's worth the complexity. Did you have something in mind?

 - By support for new authentication mechanisms, I assume you mean new
   mechanisms for authenticating variable updates? This is communicated
   in edk2 via the attributes field. Looking at patch 5 from the skiboot
   series:

+ * When the attribute EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS is set,
+ * then the Data buffer shall begin with an instance of a complete (and
+ * serialized) EFI_VARIABLE_AUTHENTICATION_2 descriptor.

   Could a new authentication scheme be communicated by setting a
   different attribute value? Or are we not carrying attributes in the
   metadata blob?

 - For addition of new variables, I'm confused as to why this would
   require a new API - wouldn't it just be exposed in the normal way via
   opal_secvar_get(_next)?

I guess I also somewhat object to calling it a 'backend' if we're using
it as a version scheme. I think the skiboot storage backends are true
backends - they provide different implementations of the same
functionality with the same API, but this seems like you're using it to
indicate different functionality. It seems like we're using it as if it
were called OPAL_SECVAR_VERSION.

>>   - What is the correct fallback behaviour if a kernel receives a result
>>     that it does not expect? If a kernel expecting BackendV1 is instead
>>     informed that it is running on BackendV2, then the cannot access the
>>     secure variable at all, so it cannot load keys that are potentially
>>     required to successfully boot (e.g. to validate the module for
>>     network card or graphics!)
>
> The backend is declaredby the firmware, and is set at compile-time. The 
> kernel queriesfirmware on whichbackend is in use, and the backend will 
> not change at runtime.If the backend in use by the firmware is not 
> supported by the kernel (e.g. kernel is too old), the kernel does not 
> attempt to read any secure variables, as it won't understand what the 
> format is. This is a secure boot failure condition, as we cannot verify 
> the next kernel. With addition of new backends in the skiboot, the 
> support will be added to the kernel. Note: skiboot and skiroot should 
> always be in sync with backend support.

Seems reasonable. I'm thinking specifically about the kernel loaded
after skiroot; and yes, on reflection just failing to boot is the only
sensible thing you can do.

Regards,
Daniel

Re: [PATCH v3 1/3] powerpc/powernv: Add OPAL API interface to get secureboot state

[Nayna]

On 06/12/2019 07:04 PM, Daniel Axtens wrote:
> Hi Nayna,
>
>>>> Since OPAL can support different types of backend which can vary in the
>>>> variable interpretation, a new OPAL API call named OPAL_SECVAR_BACKEND, is
>>>> added to retrieve the supported backend version. This helps the consumer
>>>> to know how to interpret the variable.
>>>>
>>> (Firstly, apologies that I haven't got around to asking about this yet!)
>>>
>>> Are pluggable/versioned backend a good idea?
>>>
>>> There are a few things that worry me about the idea:
>>>
>>>    - It adds complexity in crypto (or crypto-adjacent) code, and that
>>>      increases the likelihood that we'll accidentally add a bug with bad
>>>      consequences.
>> Sorry, I think I am not clear on what exactly you mean here.Can you
>> please elaborate or give specifics ?
> Cryptosystems with greater flexibility can have new kinds of
> vulnerabilities arise from the greater complexity. The first sort of
> thing that comes to mind is a downgrade attack like from TLS. I think
> you're protected from this because the mode cannot be negotiatied at run
> time, but in general it's security sensitive code so I'd like it to be
> as simple as possible.
>
>>>    - If we are worried about a long-term-future change to how secure-boot
>>>      works, would it be better to just add more get/set calls to opal at
>>>      the point at which we actually implement the new system?
>> The intention is to avoid to re-implement the key/value interface for
>> each scheme. Do you mean to deprecate the old APIs and add new APIs with
>> every scheme ?
> Yes, because I expect the scheme would change very, very rarely.

So, the design is not making the assumption that a particular scheme 
will change often. It is just allowing the flexibility for addition of 
new schemes or enhancements if needed.

>
>>>    - Under what circumstances would would we change the kernel-visible
>>>      behaviour of skiboot? Are we expecting to change the behaviour,
>>>      content or names of the variables in future? Otherwise the only
>>>      relevant change I can think of is a change to hardware platforms, and
>>>      I'm not sure how a change in hardware would lead to change in
>>>      behaviour in the kernel. Wouldn't Skiboot hide h/w differences?
>> Backends are intended to be an agreement for firmware, kernel and
>> userspace on what the format of variables are, what variables should be
>> expected, how they should be signed, etc. Though we don't expect it to
>> happen very often, we want to anticipate possible changes in the
>> firmware which may affect the kernel such as new features, support of
>> new authentication mechanisms, addition of new variables. Corresponding
>> skiboot patches are on -
>> https://lists.ozlabs.org/pipermail/skiboot/2019-June/014641.html
> I still feel like this is holding onto ongoing complexity for very
> little gain, but perhaps this is because I can't picture a specific
> change that would actually require a wholesale change to the scheme.

That is the exact reason for having pluggable backend, because we cannot 
determine now if there will be a need of new scheme in future or not.


>
> You mention new features, support for new authentication mechanisms, and
> addition of new variables.
>
>   - New features is a bit too generic to answer specifically. In general
>     I accept that there exists some new feature that would be
>     sufficiently backwards-incompatible as to require a new version. I
>     just can't think of one off the top of my head and so I'm not
>     convinced it's worth the complexity. Did you have something in mind?

That is the idea to keep the design flexible to be able to handle future 
additions with maximum reuse. Example, supporting new algorithms or a 
different handling of secure variable updates by different vendors.


>
>   - By support for new authentication mechanisms, I assume you mean new
>     mechanisms for authenticating variable updates? This is communicated
>     in edk2 via the attributes field. Looking at patch 5 from the skiboot
>     series:
>
> + * When the attribute EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS is set,
> + * then the Data buffer shall begin with an instance of a complete (and
> + * serialized) EFI_VARIABLE_AUTHENTICATION_2 descriptor.
>
>     Could a new authentication scheme be communicated by setting a
>     different attribute value? Or are we not carrying attributes in the
>     metadata blob?
>
>   - For addition of new variables, I'm confused as to why this would
>     require a new API - wouldn't it just be exposed in the normal way via
>     opal_secvar_get(_next)?

Sorry, probably it wasn't clear. By addition of new variables, we meant 
that over time we might have to add new "volatile" variables that "fine 
tunes" secure boot state. This might impact the kernel if it needs to 
understand new variables to define its policies. However, this will not 
result in change of API, it will result in change of the version.


>
> I guess I also somewhat object to calling it a 'backend' if we're using
> it as a version scheme. I think the skiboot storage backends are true
> backends - they provide different implementations of the same
> functionality with the same API, but this seems like you're using it to
> indicate different functionality. It seems like we're using it as if it
> were called OPAL_SECVAR_VERSION.

We are changing how we are exposing the version to the kernel. The 
version will be exposed as device-tree entry rather than a OPAL runtime 
service. We are not tied to the name "backend", we can switch to calling 
it as "scheme" unless there is a better name.

Thanks & Regards,
       - Nayna

Re: [PATCH v3 1/3] powerpc/powernv: Add OPAL API interface to get secureboot state

[Daniel Axtens]

Hi Nayna,

>> I guess I also somewhat object to calling it a 'backend' if we're using
>> it as a version scheme. I think the skiboot storage backends are true
>> backends - they provide different implementations of the same
>> functionality with the same API, but this seems like you're using it to
>> indicate different functionality. It seems like we're using it as if it
>> were called OPAL_SECVAR_VERSION.
>
> We are changing how we are exposing the version to the kernel. The 
> version will be exposed as device-tree entry rather than a OPAL runtime 
> service. We are not tied to the name "backend", we can switch to calling 
> it as "scheme" unless there is a better name.

This sounds like a good approach to me.

Kind regards,
Daniel

>
> Thanks & Regards,
>        - Nayna