s390/kernel: use expoline for indirect branches

BugLink: https://bugs.launchpad.net/bugs/1775477

[ Upstream commit c50c84c3 ]

The assember code in arch/s390/kernel uses a few more indirect branches
which need to be done with execute trampolines for CONFIG_EXPOLINE=y.

Cc: stable@vger.kernel.org # 4.16
Fixes: f19fbd5e ("s390: introduce execute-trampolines for branches")
Reviewed-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

arch/s390/kernel/base.S

@@ -8,18 +8,22 @@
 
 #include <linux/linkage.h>
 #include <asm/asm-offsets.h>
+#include <asm/nospec-insn.h>
 #include <asm/ptrace.h>
 #include <asm/sigp.h>
 
+	GEN_BR_THUNK %r9
+	GEN_BR_THUNK %r14
+
 ENTRY(s390_base_mcck_handler)
 	basr	%r13,0
 0:	lg	%r15,__LC_PANIC_STACK	# load panic stack
 	aghi	%r15,-STACK_FRAME_OVERHEAD
 	larl	%r1,s390_base_mcck_handler_fn
-	lg	%r1,0(%r1)
-	ltgr	%r1,%r1
+	lg	%r9,0(%r1)
+	ltgr	%r9,%r9
 	jz	1f
-	basr	%r14,%r1
+	BASR_EX	%r14,%r9
 1:	la	%r1,4095
 	lmg	%r0,%r15,__LC_GPREGS_SAVE_AREA-4095(%r1)
 	lpswe	__LC_MCK_OLD_PSW
@@ -36,10 +40,10 @@ ENTRY(s390_base_ext_handler)
 	basr	%r13,0
 0:	aghi	%r15,-STACK_FRAME_OVERHEAD
 	larl	%r1,s390_base_ext_handler_fn
-	lg	%r1,0(%r1)
-	ltgr	%r1,%r1
+	lg	%r9,0(%r1)
+	ltgr	%r9,%r9
 	jz	1f
-	basr	%r14,%r1
+	BASR_EX	%r14,%r9
 1:	lmg	%r0,%r15,__LC_SAVE_AREA_ASYNC
 	ni	__LC_EXT_OLD_PSW+1,0xfd	# clear wait state bit
 	lpswe	__LC_EXT_OLD_PSW
@@ -56,10 +60,10 @@ ENTRY(s390_base_pgm_handler)
 	basr	%r13,0
 0:	aghi	%r15,-STACK_FRAME_OVERHEAD
 	larl	%r1,s390_base_pgm_handler_fn
-	lg	%r1,0(%r1)
-	ltgr	%r1,%r1
+	lg	%r9,0(%r1)
+	ltgr	%r9,%r9
 	jz	1f
-	basr	%r14,%r1
+	BASR_EX	%r14,%r9
 	lmg	%r0,%r15,__LC_SAVE_AREA_SYNC
 	lpswe	__LC_PGM_OLD_PSW
 1:	lpswe	disabled_wait_psw-0b(%r13)
@@ -116,7 +120,7 @@ ENTRY(diag308_reset)
 	larl	%r4,.Lcontinue_psw	# Restore PSW flags
 	lpswe	0(%r4)
 .Lcontinue:
-	br	%r14
+	BR_EX	%r14
 .align 16
 .Lrestart_psw:
 	.long	0x00080000,0x80000000 + .Lrestart_part2

arch/s390/kernel/reipl.S

@@ -6,8 +6,11 @@
 
 #include <linux/linkage.h>
 #include <asm/asm-offsets.h>
+#include <asm/nospec-insn.h>
 #include <asm/sigp.h>
 
+	GEN_BR_THUNK %r14
+
 #
 # store_status
 #
@@ -62,7 +65,7 @@ ENTRY(store_status)
 	st	%r3,__LC_PSW_SAVE_AREA-SAVE_AREA_BASE + 4(%r1)
 	larl	%r2,store_status
 	stg	%r2,__LC_PSW_SAVE_AREA-SAVE_AREA_BASE + 8(%r1)
-	br	%r14
+	BR_EX	%r14
 
 	.section .bss
 	.align	8

arch/s390/kernel/swsusp.S

@@ -12,6 +12,7 @@
 #include <asm/ptrace.h>
 #include <asm/thread_info.h>
 #include <asm/asm-offsets.h>
+#include <asm/nospec-insn.h>
 #include <asm/sigp.h>
 
 /*
@@ -23,6 +24,8 @@
  * (see below) in the resume process.
  * This function runs with disabled interrupts.
  */
+	GEN_BR_THUNK %r14
+
 	.section .text
 ENTRY(swsusp_arch_suspend)
 	stmg	%r6,%r15,__SF_GPRS(%r15)
@@ -102,7 +105,7 @@ ENTRY(swsusp_arch_suspend)
 	spx	0x318(%r1)
 	lmg	%r6,%r15,STACK_FRAME_OVERHEAD + __SF_GPRS(%r15)
 	lghi	%r2,0
-	br	%r14
+	BR_EX	%r14
 
 /*
  * Restore saved memory image to correct place and restore register context.
@@ -196,11 +199,10 @@ pgm_check_entry:
 	larl	%r15,init_thread_union
 	ahi	%r15,1<<(PAGE_SHIFT+THREAD_ORDER)
 	larl	%r2,.Lpanic_string
-	larl	%r3,_sclp_print_early
 	lghi	%r1,0
 	sam31
 	sigp	%r1,%r0,SIGP_SET_ARCHITECTURE
-	basr	%r14,%r3
+	brasl	%r14,_sclp_print_early
 	larl	%r3,.Ldisabled_wait_31
 	lpsw	0(%r3)
 4:
@@ -266,7 +268,7 @@ restore_registers:
 	/* Return 0 */
 	lmg	%r6,%r15,STACK_FRAME_OVERHEAD + __SF_GPRS(%r15)
 	lghi	%r2,0
-	br	%r14
+	BR_EX	%r14
 
 	.section .data..nosave,"aw",@progbits
 	.align	8