linux-kernel - [PATCH AUTOSEL 6.0 11/44] s390/zcrypt: fix warning about field-spanning write

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Date:   Fri, 18 Nov 2022 21:10:51 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Harald Freudenberger <freude@...ux.ibm.com>,
        Jürgen Christ <jchrist@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Sasha Levin <sashal@...nel.org>, hca@...ux.ibm.com,
        agordeev@...ux.ibm.com, linux-s390@...r.kernel.org
Subject: [PATCH AUTOSEL 6.0 11/44] s390/zcrypt: fix warning about field-spanning write

From: Harald Freudenberger <freude@...ux.ibm.com>

[ Upstream commit b43088f30db1a7bff61c8486238c195c77788d6d ]

This patch fixes the warning

memcpy: detected field-spanning write (size 60) of single field "to" at drivers/s390/crypto/zcrypt_api.h:173 (size 2)
WARNING: CPU: 1 PID: 2114 at drivers/s390/crypto/zcrypt_api.h:173 prep_ep11_ap_msg+0x2c6/0x2e0 [zcrypt]

The code has been rewritten to use a union in combination
with a flex array to clearly state which part of the buffer
the payload is to be copied in via z_copy_from_user
function (which may call memcpy() in case of in-kernel calls).

Signed-off-by: Harald Freudenberger <freude@...ux.ibm.com>
Suggested-by: Jürgen Christ <jchrist@...ux.ibm.com>
Reviewed-by: Jürgen Christ <jchrist@...ux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@...ux.ibm.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/s390/crypto/zcrypt_msgtype6.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/drivers/s390/crypto/zcrypt_msgtype6.c b/drivers/s390/crypto/zcrypt_msgtype6.c
index 8fb34b8eeb18..5ad251477593 100644
--- a/drivers/s390/crypto/zcrypt_msgtype6.c
+++ b/drivers/s390/crypto/zcrypt_msgtype6.c
@@ -342,7 +342,10 @@ static int xcrb_msg_to_type6cprb_msgx(bool userspace, struct ap_message *ap_msg,
 	};
 	struct {
 		struct type6_hdr hdr;
-		struct CPRBX cprbx;
+		union {
+			struct CPRBX cprbx;
+			DECLARE_FLEX_ARRAY(u8, userdata);
+		};
 	} __packed * msg = ap_msg->msg;
 
 	int rcblen = CEIL4(xcrb->request_control_blk_length);
@@ -403,7 +406,8 @@ static int xcrb_msg_to_type6cprb_msgx(bool userspace, struct ap_message *ap_msg,
 	msg->hdr.fromcardlen2 = xcrb->reply_data_length;
 
 	/* prepare CPRB */
-	if (z_copy_from_user(userspace, &msg->cprbx, xcrb->request_control_blk_addr,
+	if (z_copy_from_user(userspace, msg->userdata,
+			     xcrb->request_control_blk_addr,
 			     xcrb->request_control_blk_length))
 		return -EFAULT;
 	if (msg->cprbx.cprb_len + sizeof(msg->hdr.function_code) >
@@ -469,9 +473,14 @@ static int xcrb_msg_to_type6_ep11cprb_msgx(bool userspace, struct ap_message *ap
 
 	struct {
 		struct type6_hdr hdr;
-		struct ep11_cprb cprbx;
-		unsigned char	pld_tag;	/* fixed value 0x30 */
-		unsigned char	pld_lenfmt;	/* payload length format */
+		union {
+			struct {
+				struct ep11_cprb cprbx;
+				unsigned char pld_tag;    /* fixed value 0x30 */
+				unsigned char pld_lenfmt; /* length format */
+			} __packed;
+			DECLARE_FLEX_ARRAY(u8, userdata);
+		};
 	} __packed * msg = ap_msg->msg;
 
 	struct pld_hdr {
@@ -500,7 +509,7 @@ static int xcrb_msg_to_type6_ep11cprb_msgx(bool userspace, struct ap_message *ap
 	msg->hdr.fromcardlen1 = xcrb->resp_len;
 
 	/* Import CPRB data from the ioctl input parameter */
-	if (z_copy_from_user(userspace, &msg->cprbx.cprb_len,
+	if (z_copy_from_user(userspace, msg->userdata,
 			     (char __force __user *)xcrb->req, xcrb->req_len)) {
 		return -EFAULT;
 	}
-- 
2.35.1