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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,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Nico Boehr <nrb@linux.ibm.com>
Subject: [PATCH 5.18 761/879] s390/perf: obtain sie_block from the right address
Date:   Tue,  7 Jun 2022 19:04:39 +0200
Message-Id: <20220607165024.953078037@linuxfoundation.org>
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References: <20220607165002.659942637@linuxfoundation.org>
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From: Nico Boehr <nrb@linux.ibm.com>

commit c9bfb460c3e4da2462e16b0f0b200990b36b1dd2 upstream.

Since commit 1179f170b6f0 ("s390: fix fpu restore in entry.S"), the
sie_block pointer is located at empty1[1], but in sie_block() it was
taken from empty1[0].

This leads to a random pointer being dereferenced, possibly causing
system crash.

This problem can be observed when running a simple guest with an endless
loop and recording the cpu-clock event:

  sudo perf kvm --guestvmlinux=<guestkernel> --guest top -e cpu-clock

With this fix, the correct guest address is shown.

Fixes: 1179f170b6f0 ("s390: fix fpu restore in entry.S")
Cc: stable@vger.kernel.org
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Nico Boehr <nrb@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/s390/kernel/perf_event.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/s390/kernel/perf_event.c
+++ b/arch/s390/kernel/perf_event.c
@@ -30,7 +30,7 @@ static struct kvm_s390_sie_block *sie_bl
 	if (!stack)
 		return NULL;
 
-	return (struct kvm_s390_sie_block *) stack->empty1[0];
+	return (struct kvm_s390_sie_block *)stack->empty1[1];
 }
 
 static bool is_in_guest(struct pt_regs *regs)