s390: scrub registers on kernel entry and KVM exit

[ 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@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index 7c6904d..b8ddc0a 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
@@ -550,6 +558,15 @@ ENTRY(pgm_check_handler)
 3:     stg     %r10,__THREAD_last_break(%r14)
 4:     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
@@ -615,6 +632,16 @@ 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
@@ -820,6 +847,16 @@ 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
@@ -982,6 +1019,16 @@ 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)