powerpc/ima: Add support to initialize ima policy rules

PowerNV systems use a Linux-based bootloader, which rely on the IMA
subsystem to enforce different secure boot modes. Since the
verification policy may differ based on the secure boot mode of the
system, the policies must be defined at runtime.

This patch implements arch-specific support to define IMA policy rules
based on the runtime secure boot mode of the system.

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

Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1572492694-6520-3-git-send-email-zohar@linux.ibm.com

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 56ea0019b61677f21685d89cb4d3bc540f091ea2..c795039bdc73b6aeecee7f610a4ea42f7e3d0afa 100644 (file)
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -938,6 +938,7 @@ config PPC_SECURE_BOOT
        prompt "Enable secure boot support"
        bool
        depends on PPC_POWERNV
+       depends on IMA_ARCH_POLICY
        help
          Systems with firmware secure boot enabled need to define security
          policies to extend secure boot to the OS. This config allows a user

diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index e2a54fa240ac787ea4fcc83a70670ffde89ed419..e8eb2955b7d5edcac056509b55adfeeaf438c699 100644 (file)
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -161,7 +161,7 @@ ifneq ($(CONFIG_PPC_POWERNV)$(CONFIG_PPC_SVM),)
 obj-y                          += ucall.o
 endif
 
-obj-$(CONFIG_PPC_SECURE_BOOT)  += secure_boot.o
+obj-$(CONFIG_PPC_SECURE_BOOT)  += secure_boot.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 (file)
index 0000000..d88913d
--- /dev/null
+++ b/arch/powerpc/kernel/ima_arch.c
@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2019 IBM Corporation
+ * Author: Nayna Jain
+ */
+
+#include <linux/ima.h>
+#include <asm/secure_boot.h>
+
+bool arch_ima_get_secureboot(void)
+{
+       return is_ppc_secureboot_enabled();
+}
+
+/*
+ * The "secure_rules" are enabled only on "secureboot" enabled systems.
+ * These rules verify the file signatures against known good values.
+ * The "appraise_type=imasig|modsig" option allows the known good signature
+ * to be stored as an xattr or as an appended signature.
+ *
+ * To avoid duplicate signature verification as much as possible, the IMA
+ * policy rule for module appraisal is added only if CONFIG_MODULE_SIG_FORCE
+ * is not enabled.
+ */
+static const char *const secure_rules[] = {
+       "appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig|modsig",
+#ifndef CONFIG_MODULE_SIG_FORCE
+       "appraise func=MODULE_CHECK appraise_type=imasig|modsig",
+#endif
+       NULL
+};
+
+/*
+ * Returns the relevant IMA arch-specific policies based on the system secure
+ * boot state.
+ */
+const char *const *arch_get_ima_policy(void)
+{
+       if (is_ppc_secureboot_enabled())
+               return secure_rules;
+
+       return NULL;
+}

diff --git a/include/linux/ima.h b/include/linux/ima.h
index 1c37f17f72035bb0437670168bfa2bfc01bbe72d..6d904754d858bd7a27145c49a1abf4145d5ce707 100644 (file)
--- 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