integrity: Eliminate weak definition of arch_get_secureboot()

security/integrity/secure_boot.c contains a single __weak function,
which breaks recordmcount when building with clang:

  $ make -skj"$(nproc)" ARCH=powerpc LLVM=1 ppc64_defconfig security/integrity/secure_boot.o
  Cannot find symbol for section 2: .text.
  security/integrity/secure_boot.o: failed

Introduce a Kconfig symbol, CONFIG_HAVE_ARCH_GET_SECUREBOOT, to indicate
that an architecture provides a definition of arch_get_secureboot().
Provide a static inline stub when this symbol is not defined to achieve
the same effect as the __weak function, allowing secure_boot.c to be
removed altogether. Move the s390 definition of arch_get_secureboot()
out of the CONFIG_KEXEC_FILE block to ensure it is always available, as
it does not actually depend on KEXEC_FILE.

Reported-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 31a6a07 ("integrity: Make arch_ima_get_secureboot integrity-wide")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

Author: nathanchance

arch/Kconfig

@@ -1841,4 +1841,7 @@ config ARCH_WANTS_PRE_LINK_VMLINUX
 config ARCH_HAS_CPU_ATTACK_VECTORS
 	bool
 
+config HAVE_ARCH_GET_SECUREBOOT
+	def_bool EFI
+
 endmenu

arch/powerpc/Kconfig

@@ -1061,6 +1061,7 @@ config PPC_SECURE_BOOT
 	depends on IMA_ARCH_POLICY
 	imply IMA_SECURE_AND_OR_TRUSTED_BOOT
 	select PSERIES_PLPKS if PPC_PSERIES
+	select HAVE_ARCH_GET_SECUREBOOT
 	help
 	  Systems with firmware secure boot enabled need to define security
 	  policies to extend secure boot to the OS. This config allows a user

arch/s390/Kconfig

@@ -181,6 +181,7 @@ config S390
 	select GENERIC_IOREMAP if PCI
 	select HAVE_ALIGNED_STRUCT_PAGE
 	select HAVE_ARCH_AUDITSYSCALL
+	select HAVE_ARCH_GET_SECUREBOOT
 	select HAVE_ARCH_JUMP_LABEL
 	select HAVE_ARCH_JUMP_LABEL_RELATIVE
 	select HAVE_ARCH_KASAN

arch/s390/kernel/ipl.c

@@ -2388,6 +2388,11 @@ void __no_stack_protector s390_reset_system(void)
 	diag_amode31_ops.diag308_reset();
 }
 
+bool arch_get_secureboot(void)
+{
+	return ipl_secure_flag;
+}
+
 #ifdef CONFIG_KEXEC_FILE
 
 int ipl_report_add_component(struct ipl_report *report, struct kexec_buf *kbuf,
@@ -2505,11 +2510,6 @@ void *ipl_report_finish(struct ipl_report *report)
 	return buf;
 }
 
-bool arch_get_secureboot(void)
-{
-	return ipl_secure_flag;
-}
-
 int ipl_report_free(struct ipl_report *report)
 {
 	struct ipl_report_component *comp, *ncomp;

include/linux/secure_boot.h

@@ -10,10 +10,14 @@
 
 #include <linux/types.h>
 
+#ifdef CONFIG_HAVE_ARCH_GET_SECUREBOOT
 /*
  * Returns true if the platform secure boot is enabled.
  * Returns false if disabled or not supported.
  */
 bool arch_get_secureboot(void);
+#else
+static inline bool arch_get_secureboot(void) { return false; }
+#endif
 
 #endif /* _LINUX_SECURE_BOOT_H */

security/integrity/Makefile

@@ -5,7 +5,7 @@
 
 obj-$(CONFIG_INTEGRITY) += integrity.o
 
-integrity-y := iint.o secure_boot.o
+integrity-y := iint.o
 integrity-$(CONFIG_INTEGRITY_AUDIT) += integrity_audit.o
 integrity-$(CONFIG_INTEGRITY_SIGNATURE) += digsig.o
 integrity-$(CONFIG_INTEGRITY_ASYMMETRIC_KEYS) += digsig_asymmetric.o