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Subject[PATCH 4/4] x86/ima: define arch_get_ima_policy() for x86
Date
This patch implements an example arch-specific IMA policy for x86 to enable
measurement and appraisal of any kernel images loaded for kexec, and
disables the kexec_load syscall.

To avoid conflicting with the existing CONFIG_KERNEL_VERIFY_SIG option, the
policy only "appraises" the target image on kexec_load. Without this, the
target kexec image would have to be verified by both the above option as
well as by IMA appraisal.

Since signature verification for kexec_load is not possible via appraisal
(or VERIFY_SIG), this results in a failure and thus effectively prevents
the kexec_load syscall from succeeding when set.

Signed-off-by: Eric Richter <erichte@linux.vnet.ibm.com>
---
arch/x86/kernel/Makefile | 2 ++
arch/x86/kernel/ima_arch.c | 27 +++++++++++++++++++++++++++
include/linux/ima.h | 8 ++++++++
security/integrity/ima/Kconfig | 8 ++++++++
4 files changed, 45 insertions(+)
create mode 100644 arch/x86/kernel/ima_arch.c

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 02d6f5cf4e7..f3e1d76ed9b 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -149,3 +149,5 @@ ifeq ($(CONFIG_X86_64),y)
obj-$(CONFIG_MMCONF_FAM10H) += mmconf-fam10h_64.o
obj-y += vsmp_64.o
endif
+
+obj-$(CONFIG_IMA_ARCH_POLICY) += ima_arch.o
diff --git a/arch/x86/kernel/ima_arch.c b/arch/x86/kernel/ima_arch.c
new file mode 100644
index 00000000000..5eb10e29db0
--- /dev/null
+++ b/arch/x86/kernel/ima_arch.c
@@ -0,0 +1,27 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (C) 2018 IBM Corporation
+ */
+#include <linux/efi.h>
+#include <linux/ima.h>
+
+extern struct boot_params boot_params;
+
+/* arch rules for audit and user mode */
+static const char * const sb_arch_rules[] = {
+#ifdef CONFIG_KEXEC_VERIFY_SIG
+ "appraise func=KEXEC_ORIG_KERNEL_CHECK appraise_type=imasig",
+#else
+ "appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig",
+#endif /* CONFIG_KEXEC_VERIFY_SIG */
+ "measure func=KEXEC_KERNEL_CHECK",
+ NULL
+};
+
+const char * const *arch_get_ima_policy(void)
+{
+ if (efi_enabled(EFI_BOOT) &&
+ (boot_params.secure_boot == efi_secureboot_mode_enabled))
+ return sb_arch_rules;
+ return NULL;
+}
diff --git a/include/linux/ima.h b/include/linux/ima.h
index 7fd272f0b1f..495fa290b14 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -30,10 +30,14 @@ extern void ima_post_path_mknod(struct dentry *dentry);
extern void ima_add_kexec_buffer(struct kimage *image);
#endif

+#if defined(CONFIG_IMA_ARCH_POLICY) && defined(CONFIG_X86)
+extern const char * const *arch_get_ima_policy(void);
+#else
static inline const char * const *arch_get_ima_policy(void)
{
return NULL;
}
+#endif

#else
static inline int ima_bprm_check(struct linux_binprm *bprm)
@@ -77,6 +81,10 @@ static inline void ima_post_path_mknod(struct dentry *dentry)
return;
}

+static inline const char * const *arch_get_ima_policy(void)
+{
+ return NULL;
+}
#endif /* CONFIG_IMA */

#ifndef CONFIG_IMA_KEXEC
diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index 13b446328dd..18de132bbda 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -157,6 +157,14 @@ config IMA_APPRAISE
<http://linux-ima.sourceforge.net>
If unsure, say N.

+config IMA_ARCH_POLICY
+ bool "Enable loading an IMA architecture specific policy"
+ depends on IMA_APPRAISE && INTEGRITY_ASYMMETRIC_KEYS
+ default n
+ help
+ This option enables loading an IMA architecture specific policy
+ based on run time secure boot flags.
+
config IMA_APPRAISE_BUILD_POLICY
bool "IMA build time configured policy rules"
depends on IMA_APPRAISE && INTEGRITY_ASYMMETRIC_KEYS
--
2.14.4
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