s390: scrub registers on kernel entry and KVM exit

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@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index 6cd444d..5d87eda 100644 (file)
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -248,6 +248,12 @@ 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
@@ -282,6 +288,8 @@ ENTRY(system_call)
 .Lsysc_vtime:
        UPDATE_VTIME %r8,%r9,__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
@@ -561,6 +569,15 @@ ENTRY(pgm_check_handler)
 4:     lgr     %r13,%r11
        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
@@ -626,6 +643,16 @@ 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
@@ -839,6 +866,16 @@ 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
@@ -1046,6 +1083,16 @@ 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)