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Subject: Re: [PATCH 6/6] s390: scrub registers on kernel entry and KVM exit
To:     Martin Schwidefsky <schwidefsky@de.ibm.com>,
        linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org,
        kvm@vger.kernel.org
Cc:     Heiko Carstens <heiko.carstens@de.ibm.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Cornelia Huck <cohuck@redhat.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jon Masters <jcm@redhat.com>,
        Marcus Meissner <meissner@suse.de>,
        Jiri Kosina <jkosina@suse.cz>
References: <1516182519-10623-1-git-send-email-schwidefsky@de.ibm.com>
 <1516182519-10623-7-git-send-email-schwidefsky@de.ibm.com>
From:   QingFeng Hao <haoqf@linux.vnet.ibm.com>
Date:   Fri, 19 Jan 2018 14:29:20 +0800
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?? 2018/1/17 17:48, Martin Schwidefsky д??:
> 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 <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)

-- 
Regards
QingFeng Hao