--- a/arch/s390/include/asm/lowcore.h
+++ b/arch/s390/include/asm/lowcore.h
@@ -141,7 +141,9 @@ struct lowcore {
 
 	/* br %r1 trampoline */
 	__u16	br_r1_trampoline;		/* 0x0400 */
-	__u8	pad_0x0402[0x0e00-0x0402];	/* 0x0402 */
+	__u32	return_lpswe;			/* 0x0402 */
+	__u32	return_mcck_lpswe;		/* 0x0406 */
+	__u8	pad_0x040a[0x0e00-0x040a];	/* 0x040a */
 
 	/*
 	 * 0xe00 contains the address of the IPL Parameter Information
--- a/arch/s390/include/asm/processor.h
+++ b/arch/s390/include/asm/processor.h
@@ -162,6 +162,7 @@ typedef struct thread_struct thread_stru
 #define INIT_THREAD {							\
 	.ksp = sizeof(init_stack) + (unsigned long) &init_stack,	\
 	.fpu.regs = (void *) init_task.thread.fpu.fprs,			\
+	.last_break = 1,						\
 }
 
 /*
--- a/arch/s390/include/asm/setup.h
+++ b/arch/s390/include/asm/setup.h
@@ -8,6 +8,7 @@
 
 #include <linux/bits.h>
 #include <uapi/asm/setup.h>
+#include <linux/build_bug.h>
 
 #define EP_OFFSET		0x10008
 #define EP_STRING		"S390EP"
@@ -155,6 +156,12 @@ static inline unsigned long kaslr_offset
 	return __kaslr_offset;
 }
 
+static inline u32 gen_lpswe(unsigned long addr)
+{
+	BUILD_BUG_ON(addr > 0xfff);
+	return 0xb2b20000 | addr;
+}
+
 #else /* __ASSEMBLY__ */
 
 #define IPL_DEVICE	(IPL_DEVICE_OFFSET)
--- a/arch/s390/kernel/asm-offsets.c
+++ b/arch/s390/kernel/asm-offsets.c
@@ -124,6 +124,8 @@ int main(void)
 	OFFSET(__LC_EXT_DAMAGE_CODE, lowcore, external_damage_code);
 	OFFSET(__LC_MCCK_FAIL_STOR_ADDR, lowcore, failing_storage_address);
 	OFFSET(__LC_LAST_BREAK, lowcore, breaking_event_addr);
+	OFFSET(__LC_RETURN_LPSWE, lowcore, return_lpswe);
+	OFFSET(__LC_RETURN_MCCK_LPSWE, lowcore, return_mcck_lpswe);
 	OFFSET(__LC_RST_OLD_PSW, lowcore, restart_old_psw);
 	OFFSET(__LC_EXT_OLD_PSW, lowcore, external_old_psw);
 	OFFSET(__LC_SVC_OLD_PSW, lowcore, svc_old_psw);
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -115,26 +115,29 @@ _LPP_OFFSET	= __LC_LPP
 
 	.macro	SWITCH_ASYNC savearea,timer
 	tmhh	%r8,0x0001		# interrupting from user ?
-	jnz	1f
+	jnz	2f
 	lgr	%r14,%r9
+	cghi	%r14,__LC_RETURN_LPSWE
+	je	0f
 	slg	%r14,BASED(.Lcritical_start)
 	clg	%r14,BASED(.Lcritical_length)
-	jhe	0f
+	jhe	1f
+0:
 	lghi	%r11,\savearea		# inside critical section, do cleanup
 	brasl	%r14,cleanup_critical
 	tmhh	%r8,0x0001		# retest problem state after cleanup
-	jnz	1f
-0:	lg	%r14,__LC_ASYNC_STACK	# are we already on the target stack?
+	jnz	2f
+1:	lg	%r14,__LC_ASYNC_STACK	# are we already on the target stack?
 	slgr	%r14,%r15
 	srag	%r14,%r14,STACK_SHIFT
-	jnz	2f
+	jnz	3f
 	CHECK_STACK \savearea
 	aghi	%r15,-(STACK_FRAME_OVERHEAD + __PT_SIZE)
-	j	3f
-1:	UPDATE_VTIME %r14,%r15,\timer
+	j	4f
+2:	UPDATE_VTIME %r14,%r15,\timer
 	BPENTER __TI_flags(%r12),_TIF_ISOLATE_BP
-2:	lg	%r15,__LC_ASYNC_STACK	# load async stack
-3:	la	%r11,STACK_FRAME_OVERHEAD(%r15)
+3:	lg	%r15,__LC_ASYNC_STACK	# load async stack
+4:	la	%r11,STACK_FRAME_OVERHEAD(%r15)
 	.endm
 
 	.macro UPDATE_VTIME w1,w2,enter_timer
@@ -401,7 +404,7 @@ ENTRY(system_call)
 	stpt	__LC_EXIT_TIMER
 	mvc	__VDSO_ECTG_BASE(16,%r14),__LC_EXIT_TIMER
 	lmg	%r11,%r15,__PT_R11(%r11)
-	lpswe	__LC_RETURN_PSW
+	b	__LC_RETURN_LPSWE(%r0)
 .Lsysc_done:
 
 #
@@ -608,43 +611,50 @@ ENTRY(pgm_check_handler)
 	BPOFF
 	stmg	%r8,%r15,__LC_SAVE_AREA_SYNC
 	lg	%r10,__LC_LAST_BREAK
-	lg	%r12,__LC_CURRENT
+	srag	%r11,%r10,12
+	jnz	0f
+	/* if __LC_LAST_BREAK is < 4096, it contains one of
+	 * the lpswe addresses in lowcore. Set it to 1 (initial state)
+	 * to prevent leaking that address to userspace.
+	 */
+	lghi	%r10,1
+0:	lg	%r12,__LC_CURRENT
 	lghi	%r11,0
 	larl	%r13,cleanup_critical
 	lmg	%r8,%r9,__LC_PGM_OLD_PSW
 	tmhh	%r8,0x0001		# test problem state bit
-	jnz	2f			# -> fault in user space
+	jnz	3f			# -> fault in user space
 #if IS_ENABLED(CONFIG_KVM)
 	# cleanup critical section for program checks in sie64a
 	lgr	%r14,%r9
 	slg	%r14,BASED(.Lsie_critical_start)
 	clg	%r14,BASED(.Lsie_critical_length)
-	jhe	0f
+	jhe	1f
 	lg	%r14,__SF_SIE_CONTROL(%r15)	# get control block pointer
 	ni	__SIE_PROG0C+3(%r14),0xfe	# no longer in SIE
 	lctlg	%c1,%c1,__LC_USER_ASCE		# load primary asce
 	larl	%r9,sie_exit			# skip forward to sie_exit
 	lghi	%r11,_PIF_GUEST_FAULT
 #endif
-0:	tmhh	%r8,0x4000		# PER bit set in old PSW ?
-	jnz	1f			# -> enabled, can't be a double fault
+1:	tmhh	%r8,0x4000		# PER bit set in old PSW ?
+	jnz	2f			# -> enabled, can't be a double fault
 	tm	__LC_PGM_ILC+3,0x80	# check for per exception
 	jnz	.Lpgm_svcper		# -> single stepped svc
-1:	CHECK_STACK __LC_SAVE_AREA_SYNC
+2:	CHECK_STACK __LC_SAVE_AREA_SYNC
 	aghi	%r15,-(STACK_FRAME_OVERHEAD + __PT_SIZE)
-	# CHECK_VMAP_STACK branches to stack_overflow or 4f
-	CHECK_VMAP_STACK __LC_SAVE_AREA_SYNC,4f
-2:	UPDATE_VTIME %r14,%r15,__LC_SYNC_ENTER_TIMER
+	# CHECK_VMAP_STACK branches to stack_overflow or 5f
+	CHECK_VMAP_STACK __LC_SAVE_AREA_SYNC,5f
+3:	UPDATE_VTIME %r14,%r15,__LC_SYNC_ENTER_TIMER
 	BPENTER __TI_flags(%r12),_TIF_ISOLATE_BP
 	lg	%r15,__LC_KERNEL_STACK
 	lgr	%r14,%r12
 	aghi	%r14,__TASK_thread	# pointer to thread_struct
 	lghi	%r13,__LC_PGM_TDB
 	tm	__LC_PGM_ILC+2,0x02	# check for transaction abort
-	jz	3f
+	jz	4f
 	mvc	__THREAD_trap_tdb(256,%r14),0(%r13)
-3:	stg	%r10,__THREAD_last_break(%r14)
-4:	lgr	%r13,%r11
+4:	stg	%r10,__THREAD_last_break(%r14)
+5:	lgr	%r13,%r11
 	la	%r11,STACK_FRAME_OVERHEAD(%r15)
 	stmg	%r0,%r7,__PT_R0(%r11)
 	# clear user controlled registers to prevent speculative use
@@ -663,14 +673,14 @@ ENTRY(pgm_check_handler)
 	stg	%r13,__PT_FLAGS(%r11)
 	stg	%r10,__PT_ARGS(%r11)
 	tm	__LC_PGM_ILC+3,0x80	# check for per exception
-	jz	5f
+	jz	6f
 	tmhh	%r8,0x0001		# kernel per event ?
 	jz	.Lpgm_kprobe
 	oi	__PT_FLAGS+7(%r11),_PIF_PER_TRAP
 	mvc	__THREAD_per_address(8,%r14),__LC_PER_ADDRESS
 	mvc	__THREAD_per_cause(2,%r14),__LC_PER_CODE
 	mvc	__THREAD_per_paid(1,%r14),__LC_PER_ACCESS_ID
-5:	REENABLE_IRQS
+6:	REENABLE_IRQS
 	xc	__SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15)
 	larl	%r1,pgm_check_table
 	llgh	%r10,__PT_INT_CODE+2(%r11)
@@ -775,7 +785,7 @@ ENTRY(io_int_handler)
 	mvc	__VDSO_ECTG_BASE(16,%r14),__LC_EXIT_TIMER
 .Lio_exit_kernel:
 	lmg	%r11,%r15,__PT_R11(%r11)
-	lpswe	__LC_RETURN_PSW
+	b	__LC_RETURN_LPSWE(%r0)
 .Lio_done:
 
 #
@@ -1214,7 +1224,7 @@ ENTRY(mcck_int_handler)
 	stpt	__LC_EXIT_TIMER
 	mvc	__VDSO_ECTG_BASE(16,%r14),__LC_EXIT_TIMER
 0:	lmg	%r11,%r15,__PT_R11(%r11)
-	lpswe	__LC_RETURN_MCCK_PSW
+	b	__LC_RETURN_MCCK_LPSWE
 
 .Lmcck_panic:
 	lg	%r15,__LC_NODAT_STACK
@@ -1271,6 +1281,8 @@ ENDPROC(stack_overflow)
 #endif
 
 ENTRY(cleanup_critical)
+	cghi	%r9,__LC_RETURN_LPSWE
+	je	.Lcleanup_lpswe
 #if IS_ENABLED(CONFIG_KVM)
 	clg	%r9,BASED(.Lcleanup_table_sie)	# .Lsie_gmap
 	jl	0f
@@ -1424,6 +1436,7 @@ ENDPROC(cleanup_critical)
 	mvc	__LC_RETURN_PSW(16),__PT_PSW(%r9)
 	mvc	0(64,%r11),__PT_R8(%r9)
 	lmg	%r0,%r7,__PT_R0(%r9)
+.Lcleanup_lpswe:
 1:	lmg	%r8,%r9,__LC_RETURN_PSW
 	BR_EX	%r14,%r11
 .Lcleanup_sysc_restore_insn:
--- a/arch/s390/kernel/process.c
+++ b/arch/s390/kernel/process.c
@@ -106,6 +106,7 @@ int copy_thread_tls(unsigned long clone_
 	p->thread.system_timer = 0;
 	p->thread.hardirq_timer = 0;
 	p->thread.softirq_timer = 0;
+	p->thread.last_break = 1;
 
 	frame->sf.back_chain = 0;
 	/* new return point is ret_from_fork */
--- a/arch/s390/kernel/setup.c
+++ b/arch/s390/kernel/setup.c
@@ -73,6 +73,7 @@
 #include <asm/nospec-branch.h>
 #include <asm/mem_detect.h>
 #include <asm/uv.h>
+#include <asm/asm-offsets.h>
 #include "entry.h"
 
 /*
@@ -450,6 +451,8 @@ static void __init setup_lowcore_dat_off
 	lc->spinlock_index = 0;
 	arch_spin_lock_setup(0);
 	lc->br_r1_trampoline = 0x07f1;	/* br %r1 */
+	lc->return_lpswe = gen_lpswe(__LC_RETURN_PSW);
+	lc->return_mcck_lpswe = gen_lpswe(__LC_RETURN_MCCK_PSW);
 
 	set_prefix((u32)(unsigned long) lc);
 	lowcore_ptr[0] = lc;
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -212,6 +212,8 @@ static int pcpu_alloc_lowcore(struct pcp
 	lc->spinlock_lockval = arch_spin_lockval(cpu);
 	lc->spinlock_index = 0;
 	lc->br_r1_trampoline = 0x07f1;	/* br %r1 */
+	lc->return_lpswe = gen_lpswe(__LC_RETURN_PSW);
+	lc->return_mcck_lpswe = gen_lpswe(__LC_RETURN_MCCK_PSW);
 	if (nmi_alloc_per_cpu(lc))
 		goto out_async;
 	if (vdso_alloc_per_cpu(lc))
--- a/arch/s390/mm/vmem.c
+++ b/arch/s390/mm/vmem.c
@@ -415,6 +415,10 @@ void __init vmem_map_init(void)
 		     SET_MEMORY_RO | SET_MEMORY_X);
 	__set_memory(__stext_dma, (__etext_dma - __stext_dma) >> PAGE_SHIFT,
 		     SET_MEMORY_RO | SET_MEMORY_X);
+
+	/* we need lowcore executable for our LPSWE instructions */
+	set_memory_x(0, 1);
+
 	pr_info("Write protected kernel read-only data: %luk\n",
 		(unsigned long)(__end_rodata - _stext) >> 10);
 }
