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Date:   Fri, 27 Apr 2018 15:58:15 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>
Subject: [PATCH 4.4 13/50] s390: scrub registers on kernel entry and KVM exit

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Martin Schwidefsky <schwidefsky@...ibm.com>


[ Upstream commit 7041d28115e91f2144f811ffe8a195c696b1e1d0 ]

Clear all user space registers on entry to the kernel and all KVM guest
registers on KVM guest exit if the register does not contain either a
parameter or a result value.

Reviewed-by: Christian Borntraeger <borntraeger@...ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/s390/kernel/entry.S |   47 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)

--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -244,6 +244,12 @@ ENTRY(sie64a)
 sie_exit:
 	lg	%r14,__SF_EMPTY+8(%r15)		# load guest register save area
 	stmg	%r0,%r13,0(%r14)		# save guest gprs 0-13
+	xgr	%r0,%r0				# clear guest registers to
+	xgr	%r1,%r1				# prevent speculative use
+	xgr	%r2,%r2
+	xgr	%r3,%r3
+	xgr	%r4,%r4
+	xgr	%r5,%r5
 	lmg	%r6,%r14,__SF_GPRS(%r15)	# restore kernel registers
 	lg	%r2,__SF_EMPTY+16(%r15)		# return exit reason code
 	br	%r14
@@ -277,6 +283,8 @@ ENTRY(system_call)
 .Lsysc_vtime:
 	UPDATE_VTIME %r10,%r13,__LC_SYNC_ENTER_TIMER
 	stmg	%r0,%r7,__PT_R0(%r11)
+	# clear user controlled register to prevent speculative use
+	xgr	%r0,%r0
 	mvc	__PT_R8(64,%r11),__LC_SAVE_AREA_SYNC
 	mvc	__PT_PSW(16,%r11),__LC_SVC_OLD_PSW
 	mvc	__PT_INT_CODE(4,%r11),__LC_SVC_ILC
@@ -504,6 +512,15 @@ ENTRY(pgm_check_handler)
 	mvc	__THREAD_trap_tdb(256,%r14),0(%r13)
 3:	la	%r11,STACK_FRAME_OVERHEAD(%r15)
 	stmg	%r0,%r7,__PT_R0(%r11)
+	# clear user controlled registers to prevent speculative use
+	xgr	%r0,%r0
+	xgr	%r1,%r1
+	xgr	%r2,%r2
+	xgr	%r3,%r3
+	xgr	%r4,%r4
+	xgr	%r5,%r5
+	xgr	%r6,%r6
+	xgr	%r7,%r7
 	mvc	__PT_R8(64,%r11),__LC_SAVE_AREA_SYNC
 	stmg	%r8,%r9,__PT_PSW(%r11)
 	mvc	__PT_INT_CODE(4,%r11),__LC_PGM_ILC
@@ -567,6 +584,16 @@ ENTRY(io_int_handler)
 	lmg	%r8,%r9,__LC_IO_OLD_PSW
 	SWITCH_ASYNC __LC_SAVE_AREA_ASYNC,__LC_ASYNC_ENTER_TIMER
 	stmg	%r0,%r7,__PT_R0(%r11)
+	# clear user controlled registers to prevent speculative use
+	xgr	%r0,%r0
+	xgr	%r1,%r1
+	xgr	%r2,%r2
+	xgr	%r3,%r3
+	xgr	%r4,%r4
+	xgr	%r5,%r5
+	xgr	%r6,%r6
+	xgr	%r7,%r7
+	xgr	%r10,%r10
 	mvc	__PT_R8(64,%r11),__LC_SAVE_AREA_ASYNC
 	stmg	%r8,%r9,__PT_PSW(%r11)
 	mvc	__PT_INT_CODE(12,%r11),__LC_SUBCHANNEL_ID
@@ -742,6 +769,16 @@ ENTRY(ext_int_handler)
 	lmg	%r8,%r9,__LC_EXT_OLD_PSW
 	SWITCH_ASYNC __LC_SAVE_AREA_ASYNC,__LC_ASYNC_ENTER_TIMER
 	stmg	%r0,%r7,__PT_R0(%r11)
+	# clear user controlled registers to prevent speculative use
+	xgr	%r0,%r0
+	xgr	%r1,%r1
+	xgr	%r2,%r2
+	xgr	%r3,%r3
+	xgr	%r4,%r4
+	xgr	%r5,%r5
+	xgr	%r6,%r6
+	xgr	%r7,%r7
+	xgr	%r10,%r10
 	mvc	__PT_R8(64,%r11),__LC_SAVE_AREA_ASYNC
 	stmg	%r8,%r9,__PT_PSW(%r11)
 	lghi	%r1,__LC_EXT_PARAMS2
@@ -908,6 +945,16 @@ ENTRY(mcck_int_handler)
 .Lmcck_skip:
 	lghi	%r14,__LC_GPREGS_SAVE_AREA+64
 	stmg	%r0,%r7,__PT_R0(%r11)
+	# clear user controlled registers to prevent speculative use
+	xgr	%r0,%r0
+	xgr	%r1,%r1
+	xgr	%r2,%r2
+	xgr	%r3,%r3
+	xgr	%r4,%r4
+	xgr	%r5,%r5
+	xgr	%r6,%r6
+	xgr	%r7,%r7
+	xgr	%r10,%r10
 	mvc	__PT_R8(64,%r11),0(%r14)
 	stmg	%r8,%r9,__PT_PSW(%r11)
 	xc	__PT_FLAGS(8,%r11),__PT_FLAGS(%r11)


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