linux-kernel - [PATCH 3.16 020/202] sd: Clear PS bit before Mode Select.

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Message-ID: <lsq.1556377989.238780757@decadent.org.uk>
Date:   Sat, 27 Apr 2019 16:13:09 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "Gabriel Krisman Bertazi" <krisman@...ux.vnet.ibm.com>
Subject: [PATCH 3.16 020/202] sd: Clear PS bit before Mode Select.

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

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

From: Gabriel Krisman Bertazi <krisman@...ux.vnet.ibm.com>

commit 2c5d16d6a9e7218e57b716e4fd9d77c776d21471 upstream.

According to SPC-4, in a Mode Select, the PS bit in Mode Pages is
reserved and must be set to 0 by the driver.  In the sd implementation,
function cache_type_store does a Mode Sense, which might set the PS bit
on the read buffer, followed by a Mode Select, which receives the same
buffer, without explicitly clearing the PS bit.  So, in cases where
target supports saving the Mode Page to a non-volatile location, we end
up doing a Mode Select with the PS bit set, which could cause an illegal
request error if the target is checking this.

This was observed on a new firmware change, which was subsequently
reverted, but this changes sd.c to be more compliant with SPC-4.

This patch clears the PS bit in the buffer returned by Mode Select,
right before it is used in the Mode Select command.

Signed-off-by: Gabriel Krisman Bertazi <krisman@...ux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@...cle.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/scsi/sd.c | 1 +
 1 file changed, 1 insertion(+)

--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -192,6 +192,7 @@ cache_type_store(struct device *dev, str
 	buffer_data[2] &= ~0x05;
 	buffer_data[2] |= wce << 2 | rcd;
 	sp = buffer_data[0] & 0x80 ? 1 : 0;
+	buffer_data[0] &= ~0x80;

 	if (scsi_mode_select(sdp, 1, sp, 8, buffer_data, len, SD_TIMEOUT,
 			     SD_MAX_RETRIES, &data, &sshdr)) {