[PATCH 6/6] s390: scrub registers on kernel entry and KVM exit

Martin Schwidefsky
2018-01-17T09:48:39Z

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.

Suggested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---
arch/s390/kernel/entry.S | 41 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 41 insertions(+)

diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index 2a22c03..47227d3 100644
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -322,6 +322,12 @@ 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
+ xgr %r1,%r1
+ 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
@@ -358,6 +364,7 @@ ENTRY(system_call)
UPDATE_VTIME %r8,%r9,__LC_SYNC_ENTER_TIMER
BPENTER __TI_flags(%r12),_TIF_NOBP
stmg %r0,%r7,__PT_R0(%r11)
+ 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
@@ -640,6 +647,14 @@ ENTRY(pgm_check_handler)
4: lgr %r13,%r11
la %r11,STACK_FRAME_OVERHEAD(%r15)
stmg %r0,%r7,__PT_R0(%r11)
+ xgr %r0,%r0 # clear user space registers
+ 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
@@ -706,6 +721,15 @@ 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)
+ xgr %r0,%r0 # clear user space registers
+ 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
@@ -924,6 +948,15 @@ 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)
+ xgr %r0,%r0 # clear user space registers
+ 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
@@ -1133,6 +1166,14 @@ ENTRY(mcck_int_handler)
.Lmcck_skip:
lghi %r14,__LC_GPREGS_SAVE_AREA+64
stmg %r0,%r7,__PT_R0(%r11)
+ xgr %r0,%r0 # clear user space registers
+ 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)
--
2.7.4