7 files changed, 76 insertions, 5 deletions
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index a492376d6e3f..115b8cddefee 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -585,6 +585,7 @@ config KERNEL_NOBP
 
 config EXPOLINE
 	def_bool n
+	depends on $(cc-option,-mindirect-branch=thunk)
 	prompt "Avoid speculative indirect branches in the kernel"
 	help
 	  Compile the kernel with the expoline compiler options to guard
@@ -595,6 +596,20 @@ config EXPOLINE
 
 	  If unsure, say N.
 
+config EXPOLINE_EXTERN
+	def_bool n
+	depends on EXPOLINE
+	depends on HAVE_MARCH_Z10_FEATURES
+	depends on CC_IS_GCC && GCC_VERSION >= 110200
+	depends on $(success,$(srctree)/arch/s390/tools/gcc-thunk-extern.sh $(CC))
+	prompt "Generate expolines as extern functions."
+	help
+	  This option is required for some tooling like kpatch. The kernel is
+	  compiled with -mindirect-branch=thunk-extern and requires a newer
+	  compiler.
+
+	  If unsure, say N.
+
 choice
 	prompt "Expoline default"
 	depends on EXPOLINE
diff --git a/arch/s390/Makefile b/arch/s390/Makefile
index 2edf25b44c4b..bd75128b7d79 100644
--- a/arch/s390/Makefile
+++ b/arch/s390/Makefile
@@ -81,14 +81,18 @@ ifneq ($(call cc-option,-mstack-size=8192 -mstack-guard=128),)
 endif
 
 ifdef CONFIG_EXPOLINE
-  ifneq ($(call cc-option,$(CC_FLAGS_MARCH) -mindirect-branch=thunk),)
+  ifdef CONFIG_EXPOLINE_EXTERN
+    KBUILD_LDFLAGS_MODULE += arch/s390/lib/expoline.o
+    CC_FLAGS_EXPOLINE := -mindirect-branch=thunk-extern
+    CC_FLAGS_EXPOLINE += -mfunction-return=thunk-extern
+  else
     CC_FLAGS_EXPOLINE := -mindirect-branch=thunk
     CC_FLAGS_EXPOLINE += -mfunction-return=thunk
-    CC_FLAGS_EXPOLINE += -mindirect-branch-table
-    export CC_FLAGS_EXPOLINE
-    cflags-y += $(CC_FLAGS_EXPOLINE) -DCC_USING_EXPOLINE
-    aflags-y += -DCC_USING_EXPOLINE
   endif
+  CC_FLAGS_EXPOLINE += -mindirect-branch-table
+  export CC_FLAGS_EXPOLINE
+  cflags-y += $(CC_FLAGS_EXPOLINE) -DCC_USING_EXPOLINE
+  aflags-y += -DCC_USING_EXPOLINE
 endif
 
 ifdef CONFIG_FUNCTION_TRACER
diff --git a/arch/s390/include/asm/nospec-insn.h b/arch/s390/include/asm/nospec-insn.h
index 4397eae15e34..bbb5c4d84db9 100644
--- a/arch/s390/include/asm/nospec-insn.h
+++ b/arch/s390/include/asm/nospec-insn.h
@@ -18,7 +18,11 @@ _LC_BR_R1 = __LC_BR_R1
  * the various thunks are merged into a single copy.
  */
 	.macro __THUNK_PROLOG_NAME name
+#ifdef CONFIG_EXPOLINE_EXTERN
+	.pushsection .text,"ax",@progbits
+#else
 	.pushsection .text.\name,"axG",@progbits,\name,comdat
+#endif
 	.globl \name
 	.hidden \name
 	.type \name,@function
@@ -115,7 +119,13 @@ _LC_BR_R1 = __LC_BR_R1
 555:	br	\reg
 	.endm
 
+#ifdef CONFIG_EXPOLINE_EXTERN
+	.macro GEN_BR_THUNK reg,ruse=%r1
+	.endm
+	.macro GEN_BR_THUNK_EXTERN reg,ruse=%r1
+#else
 	.macro GEN_BR_THUNK reg,ruse=%r1
+#endif
 	__DECODE_RR __THUNK_PROLOG_BR,\reg,\ruse
 	__THUNK_EX_BR \reg,\ruse
 	__THUNK_EPILOG
diff --git a/arch/s390/lib/Makefile b/arch/s390/lib/Makefile
index 69feb8ed3312..5d415b3db6d1 100644
--- a/arch/s390/lib/Makefile
+++ b/arch/s390/lib/Makefile
@@ -7,6 +7,7 @@ lib-y += delay.o string.o uaccess.o find.o spinlock.o
 obj-y += mem.o xor.o
 lib-$(CONFIG_KPROBES) += probes.o
 lib-$(CONFIG_UPROBES) += probes.o
+obj-$(CONFIG_EXPOLINE_EXTERN) += expoline.o
 obj-$(CONFIG_S390_KPROBES_SANITY_TEST) += test_kprobes_s390.o
 test_kprobes_s390-objs += test_kprobes_asm.o test_kprobes.o
 
diff --git a/arch/s390/lib/expoline.S b/arch/s390/lib/expoline.S
new file mode 100644
index 000000000000..92ed8409a7a4
--- /dev/null
+++ b/arch/s390/lib/expoline.S
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <asm/nospec-insn.h>
+#include <linux/linkage.h>
+
+.macro GEN_ALL_BR_THUNK_EXTERN
+	.irp r1,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
+	GEN_BR_THUNK_EXTERN %r\r1
+	.endr
+.endm
+
+GEN_ALL_BR_THUNK_EXTERN
diff --git a/arch/s390/tools/gcc-thunk-extern.sh b/arch/s390/tools/gcc-thunk-extern.sh
new file mode 100755
index 000000000000..20bcbf6dd7ab
--- /dev/null
+++ b/arch/s390/tools/gcc-thunk-extern.sh
@@ -0,0 +1,24 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# Borrowed from gcc: gcc/testsuite/gcc.target/s390/nobp-section-type-conflict.c
+# Checks that we don't get error: section type conflict with ‘put_page’.
+
+cat << "END" | $@ -x c - -fno-PIE -march=z10 -mindirect-branch=thunk-extern -mfunction-return=thunk-extern -mindirect-branch-table -O2 -c -o /dev/null
+int a;
+int b (void);
+void c (int);
+
+static void
+put_page (void)
+{
+  if (b ())
+    c (a);
+}
+
+__attribute__ ((__section__ (".init.text"), __cold__)) void
+d (void)
+{
+  put_page ();
+  put_page ();
+}
+END
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 6bfa33217914..dbc0aaf69e43 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -658,6 +658,11 @@ static int ignore_undef_symbol(struct elf_info *info, const char *symname)
 		    strstarts(symname, "_savevr_") ||
 		    strcmp(symname, ".TOC.") == 0)
 			return 1;
+
+	if (info->hdr->e_machine == EM_S390)
+		/* Expoline thunks are linked on all kernel modules during final link of .ko */
+		if (strstarts(symname, "__s390_indirect_jump_r"))
+			return 1;
 	/* Do not ignore this symbol */
 	return 0;
 }