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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Heiko Carstens <hca@linux.ibm.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.10 58/63] s390: always clear kernel stack backchain before calling functions
Date:   Mon,  4 Jan 2021 16:57:51 +0100
Message-Id: <20210104155711.617987277@linuxfoundation.org>
In-Reply-To: <20210104155708.800470590@linuxfoundation.org>
References: <20210104155708.800470590@linuxfoundation.org>
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From: Heiko Carstens <hca@linux.ibm.com>

[ Upstream commit 9365965db0c7ca7fc81eee27c21d8522d7102c32 ]

Clear the kernel stack backchain before potentially calling the
lockdep trace_hardirqs_off/on functions. Without this walking the
kernel backchain, e.g. during a panic, might stop too early.

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/s390/kernel/entry.S | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index 6343dca0dbeb6..71203324ff42b 100644
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -406,6 +406,7 @@ ENTRY(system_call)
 	mvc	__PT_PSW(16,%r11),__LC_SVC_OLD_PSW
 	mvc	__PT_INT_CODE(4,%r11),__LC_SVC_ILC
 	stg	%r14,__PT_FLAGS(%r11)
+	xc	__SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15)
 	ENABLE_INTS
 .Lsysc_do_svc:
 	# clear user controlled register to prevent speculative use
@@ -422,7 +423,6 @@ ENTRY(system_call)
 	jnl	.Lsysc_nr_ok
 	slag	%r8,%r1,3
 .Lsysc_nr_ok:
-	xc	__SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15)
 	stg	%r2,__PT_ORIG_GPR2(%r11)
 	stg	%r7,STACK_FRAME_OVERHEAD(%r15)
 	lg	%r9,0(%r8,%r10)			# get system call add.
@@ -712,8 +712,8 @@ ENTRY(pgm_check_handler)
 	mvc	__THREAD_per_address(8,%r14),__LC_PER_ADDRESS
 	mvc	__THREAD_per_cause(2,%r14),__LC_PER_CODE
 	mvc	__THREAD_per_paid(1,%r14),__LC_PER_ACCESS_ID
-6:	RESTORE_SM_CLEAR_PER
-	xc	__SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15)
+6:	xc	__SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15)
+	RESTORE_SM_CLEAR_PER
 	larl	%r1,pgm_check_table
 	llgh	%r10,__PT_INT_CODE+2(%r11)
 	nill	%r10,0x007f
@@ -734,8 +734,8 @@ ENTRY(pgm_check_handler)
 # PER event in supervisor state, must be kprobes
 #
 .Lpgm_kprobe:
-	RESTORE_SM_CLEAR_PER
 	xc	__SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15)
+	RESTORE_SM_CLEAR_PER
 	lgr	%r2,%r11		# pass pointer to pt_regs
 	brasl	%r14,do_per_trap
 	j	.Lpgm_return
@@ -777,10 +777,10 @@ ENTRY(io_int_handler)
 	stmg	%r8,%r9,__PT_PSW(%r11)
 	mvc	__PT_INT_CODE(12,%r11),__LC_SUBCHANNEL_ID
 	xc	__PT_FLAGS(8,%r11),__PT_FLAGS(%r11)
+	xc	__SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15)
 	TSTMSK	__LC_CPU_FLAGS,_CIF_IGNORE_IRQ
 	jo	.Lio_restore
 	TRACE_IRQS_OFF
-	xc	__SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15)
 .Lio_loop:
 	lgr	%r2,%r11		# pass pointer to pt_regs
 	lghi	%r3,IO_INTERRUPT
@@ -980,10 +980,10 @@ ENTRY(ext_int_handler)
 	mvc	__PT_INT_PARM(4,%r11),__LC_EXT_PARAMS
 	mvc	__PT_INT_PARM_LONG(8,%r11),0(%r1)
 	xc	__PT_FLAGS(8,%r11),__PT_FLAGS(%r11)
+	xc	__SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15)
 	TSTMSK	__LC_CPU_FLAGS,_CIF_IGNORE_IRQ
 	jo	.Lio_restore
 	TRACE_IRQS_OFF
-	xc	__SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15)
 	lgr	%r2,%r11		# pass pointer to pt_regs
 	lghi	%r3,EXT_INTERRUPT
 	brasl	%r14,do_IRQ
-- 
2.27.0