linux-kernel - [PATCH 3.4 016/107] s390/sclp: clear upper register halves in _sclp_print

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Date:	Wed, 16 Mar 2016 16:05:10 +0800
From:	lizf@...nel.org
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Zefan Li <lizefan@...wei.com>
Subject: [PATCH 3.4 016/107] s390/sclp: clear upper register halves in _sclp_print_early

From: Martin Schwidefsky <schwidefsky@...ibm.com>

3.4.111-rc1 review patch.  If anyone has any objections, please let me know.

------------------


commit f9c87a6f46d508eae0d9ae640be98d50f237f827 upstream.

If the kernel is compiled with gcc 5.1 and the XZ compression option
the decompress_kernel function calls _sclp_print_early in 64-bit mode
while the content of the upper register half of %r6 is non-zero.
This causes a specification exception on the servc instruction in
_sclp_servc.

The _sclp_print_early function saves and restores the upper registers
halves but it fails to clear them for the 31-bit code of the mini sclp
driver.

Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>
Signed-off-by: Zefan Li <lizefan@...wei.com>
---
 arch/s390/kernel/sclp.S | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/s390/kernel/sclp.S b/arch/s390/kernel/sclp.S
index 95792d8..51ca1c3 100644
--- a/arch/s390/kernel/sclp.S
+++ b/arch/s390/kernel/sclp.S
@@ -270,6 +270,8 @@ ENTRY(_sclp_print_early)
 	jno	.Lesa2
 	ahi	%r15,-80
 	stmh	%r6,%r15,96(%r15)		# store upper register halves
+	basr	%r13,0
+	lmh	%r0,%r15,.Lzeroes-.(%r13)	# clear upper register halves
 .Lesa2:
 #endif
 	lr	%r10,%r2			# save string pointer
@@ -293,6 +295,8 @@ ENTRY(_sclp_print_early)
 #endif
 	lm	%r6,%r15,120(%r15)		# restore registers
 	br	%r14
+.Lzeroes:
+	.fill	64,4,0
 
 .LwritedataS4:
 	.long	0x00760005			# SCLP command for write data
-- 
1.9.1