[PATCH v5 2/2] powerpc: Add support to initialize ima policy rules

[Nayna Jain <nayna@linux.ibm.com>]

POWER 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           |  2 ++
 arch/powerpc/kernel/Makefile   |  2 +-
 arch/powerpc/kernel/ima_arch.c | 50 ++++++++++++++++++++++++++++++++++
 include/linux/ima.h            |  3 +-
 4 files changed, 55 insertions(+), 2 deletions(-)
 create mode 100644 arch/powerpc/kernel/ima_arch.c

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index c902a39124dc..42109682b727 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -917,6 +917,8 @@ config PPC_SECURE_BOOT
 	bool
 	default n
 	depends on PPC64
+	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
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index d310ebb4e526..520b1c814197 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -157,7 +157,7 @@ endif
 obj-$(CONFIG_EPAPR_PARAVIRT)	+= epapr_paravirt.o epapr_hcalls.o
 obj-$(CONFIG_KVM_GUEST)		+= kvm.o kvm_emul.o
 
-obj-$(CONFIG_PPC_SECURE_BOOT)	+= secboot.o
+obj-$(CONFIG_PPC_SECURE_BOOT)	+= secboot.o ima_arch.o
 
 # Disable GCOV, KCOV & sanitizers in odd or sensitive code
 GCOV_PROFILE_prom_init.o := n
diff --git a/arch/powerpc/kernel/ima_arch.c b/arch/powerpc/kernel/ima_arch.c
new file mode 100644
index 000000000000..ac90fac83338
--- /dev/null
+++ b/arch/powerpc/kernel/ima_arch.c
@@ -0,0 +1,50 @@
+// 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)
+{
+	return get_powerpc_secureboot();
+}
+
+/*
+ * File signature verification is not needed, include only measurements
+ */
+static const char *const default_arch_rules[] = {
+	"measure func=KEXEC_KERNEL_CHECK",
+	"measure func=MODULE_CHECK",
+	NULL
+};
+
+/* Both file signature verification and measurements are needed */
+static const char *const sb_arch_rules[] = {
+	"measure func=KEXEC_KERNEL_CHECK template=ima-modsig",
+	"appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig|modsig",
+#if IS_ENABLED(CONFIG_MODULE_SIG)
+	"measure func=MODULE_CHECK",
+#else
+	"measure func=MODULE_CHECK template=ima-modsig",
+	"appraise func=MODULE_CHECK appraise_type=imasig|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 a20ad398d260..10af09b5b478 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -29,7 +29,8 @@ extern void ima_kexec_cmdline(const void *buf, int size);
 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