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

[QingFeng Hao]

在 2018/1/17 17:48, Martin Schwidefsky 写道:

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.

I am not sure if I understand this but it will be safer?
And can we abstract the operations to be a macro like CLEAR_REG_7?
Thanks

Suggested-by: Christian Borntraeger <borntrae...@de.ibm.com>
Reviewed-by: Christian Borntraeger <borntrae...@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidef...@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)

--
Regards
QingFeng Hao