[char-misc-next v2 2/2] mei: revamp mei extension header structure layout.

[Tomas Winkler <tomas.winkler@intel.com>]

The mei extension header was build as array of flexible structures
which will not work if actually more headers are added.
(Currently only vtag header was used).
Sparse reports:

drivers/misc/mei/hw.h:253:32: warning: array of flexible structures

Use basic type u8 for the variable sized extension.
Define explicitly mei_ext_hdr_vtag structure.
And also fix mei_ext_next() function to point correctly to the
end of the header.

Note: the headers are part of firmware interface and need to be __packed.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
---
V2:
1. Move kdoc fix to a different patch.
2. Update the commit message.

 drivers/misc/mei/client.c    | 16 +++++++++-------
 drivers/misc/mei/hw.h        | 26 +++++++++++++++++++-------
 drivers/misc/mei/interrupt.c | 23 ++++++++++-------------
 3 files changed, 38 insertions(+), 27 deletions(-)

diff --git a/drivers/misc/mei/client.c b/drivers/misc/mei/client.c
index 18e49479d8b0..96f4e59c32a5 100644
--- a/drivers/misc/mei/client.c
+++ b/drivers/misc/mei/client.c
@@ -1726,12 +1726,15 @@ int mei_cl_read_start(struct mei_cl *cl, size_t length, const struct file *fp)
 	return rets;
 }
 
-static inline u8 mei_ext_hdr_set_vtag(struct mei_ext_hdr *ext, u8 vtag)
+static inline u8 mei_ext_hdr_set_vtag(void *ext, u8 vtag)
 {
-	ext->type = MEI_EXT_HDR_VTAG;
-	ext->ext_payload[0] = vtag;
-	ext->length = mei_data2slots(sizeof(*ext));
-	return ext->length;
+	struct mei_ext_hdr_vtag *vtag_hdr = ext;
+
+	vtag_hdr->hdr.type = MEI_EXT_HDR_VTAG;
+	vtag_hdr->hdr.length = mei_data2slots(sizeof(*vtag_hdr));
+	vtag_hdr->vtag = vtag;
+	vtag_hdr->reserved = 0;
+	return vtag_hdr->hdr.length;
 }
 
 /**
@@ -1745,7 +1748,6 @@ static struct mei_msg_hdr *mei_msg_hdr_init(const struct mei_cl_cb *cb)
 {
 	size_t hdr_len;
 	struct mei_ext_meta_hdr *meta;
-	struct mei_ext_hdr *ext;
 	struct mei_msg_hdr *mei_hdr;
 	bool is_ext, is_vtag;
 
@@ -1764,7 +1766,7 @@ static struct mei_msg_hdr *mei_msg_hdr_init(const struct mei_cl_cb *cb)
 
 	hdr_len += sizeof(*meta);
 	if (is_vtag)
-		hdr_len += sizeof(*ext);
+		hdr_len += sizeof(struct mei_ext_hdr_vtag);
 
 setup_hdr:
 	mei_hdr = kzalloc(hdr_len, GFP_KERNEL);
diff --git a/drivers/misc/mei/hw.h b/drivers/misc/mei/hw.h
index 47ef2429a4bc..dfd60c916da0 100644
--- a/drivers/misc/mei/hw.h
+++ b/drivers/misc/mei/hw.h
@@ -235,9 +235,8 @@ enum mei_ext_hdr_type {
 struct mei_ext_hdr {
 	u8 type;
 	u8 length;
-	u8 ext_payload[2];
-	u8 hdr[];
-};
+	u8 data[];
+} __packed;
 
 /**
  * struct mei_ext_meta_hdr - extend header meta data
@@ -250,8 +249,21 @@ struct mei_ext_meta_hdr {
 	u8 count;
 	u8 size;
 	u8 reserved[2];
-	struct mei_ext_hdr hdrs[];
-};
+	u8 hdrs[];
+} __packed;
+
+/**
+ * struct mei_ext_hdr_vtag - extend header for vtag
+ *
+ * @hdr: standard extend header
+ * @vtag: virtual tag
+ * @reserved: reserved
+ */
+struct mei_ext_hdr_vtag {
+	struct mei_ext_hdr hdr;
+	u8 vtag;
+	u8 reserved;
+} __packed;
 
 /*
  * Extended header iterator functions
@@ -266,7 +278,7 @@ struct mei_ext_meta_hdr {
  */
 static inline struct mei_ext_hdr *mei_ext_begin(struct mei_ext_meta_hdr *meta)
 {
-	return meta->hdrs;
+	return (struct mei_ext_hdr *)meta->hdrs;
 }
 
 /**
@@ -295,7 +307,7 @@ static inline bool mei_ext_last(struct mei_ext_meta_hdr *meta,
  */
 static inline struct mei_ext_hdr *mei_ext_next(struct mei_ext_hdr *ext)
 {
-	return (struct mei_ext_hdr *)(ext->hdr + (ext->length * 4));
+	return (struct mei_ext_hdr *)((u8 *)ext + (ext->length * 4));
 }
 
 /**
diff --git a/drivers/misc/mei/interrupt.c b/drivers/misc/mei/interrupt.c
index aab3ebfa9fc4..a67f4f2d33a9 100644
--- a/drivers/misc/mei/interrupt.c
+++ b/drivers/misc/mei/interrupt.c
@@ -123,13 +123,13 @@ static int mei_cl_irq_read_msg(struct mei_cl *cl,
 
 	if (mei_hdr->extended) {
 		struct mei_ext_hdr *ext;
-		struct mei_ext_hdr *vtag = NULL;
+		struct mei_ext_hdr_vtag *vtag_hdr = NULL;
 
 		ext = mei_ext_begin(meta);
 		do {
 			switch (ext->type) {
 			case MEI_EXT_HDR_VTAG:
-				vtag = ext;
+				vtag_hdr = (struct mei_ext_hdr_vtag *)ext;
 				break;
 			case MEI_EXT_HDR_NONE:
 				fallthrough;
@@ -141,20 +141,20 @@ static int mei_cl_irq_read_msg(struct mei_cl *cl,
 			ext = mei_ext_next(ext);
 		} while (!mei_ext_last(meta, ext));
 
-		if (!vtag) {
+		if (!vtag_hdr) {
 			cl_dbg(dev, cl, "vtag not found in extended header.\n");
 			cb->status = -EPROTO;
 			goto discard;
 		}
 
-		cl_dbg(dev, cl, "vtag: %d\n", vtag->ext_payload[0]);
-		if (cb->vtag && cb->vtag != vtag->ext_payload[0]) {
+		cl_dbg(dev, cl, "vtag: %d\n", vtag_hdr->vtag);
+		if (cb->vtag && cb->vtag != vtag_hdr->vtag) {
 			cl_err(dev, cl, "mismatched tag: %d != %d\n",
-			       cb->vtag, vtag->ext_payload[0]);
+			       cb->vtag, vtag_hdr->vtag);
 			cb->status = -EPROTO;
 			goto discard;
 		}
-		cb->vtag = vtag->ext_payload[0];
+		cb->vtag = vtag_hdr->vtag;
 	}
 
 	if (!mei_cl_is_connected(cl)) {
@@ -331,7 +331,6 @@ int mei_irq_read_handler(struct mei_device *dev,
 	struct mei_ext_meta_hdr *meta_hdr = NULL;
 	struct mei_cl *cl;
 	int ret;
-	u32 ext_meta_hdr_u32;
 	u32 hdr_size_left;
 	u32 hdr_size_ext;
 	int i;
@@ -367,14 +366,12 @@ int mei_irq_read_handler(struct mei_device *dev,
 
 	if (mei_hdr->extended) {
 		if (!dev->rd_msg_hdr[1]) {
-			ext_meta_hdr_u32 = mei_read_hdr(dev);
-			dev->rd_msg_hdr[1] = ext_meta_hdr_u32;
+			dev->rd_msg_hdr[1] = mei_read_hdr(dev);
 			dev->rd_msg_hdr_count++;
 			(*slots)--;
-			dev_dbg(dev->dev, "extended header is %08x\n",
-				ext_meta_hdr_u32);
+			dev_dbg(dev->dev, "extended header is %08x\n", dev->rd_msg_hdr[1]);
 		}
-		meta_hdr = ((struct mei_ext_meta_hdr *)dev->rd_msg_hdr + 1);
+		meta_hdr = ((struct mei_ext_meta_hdr *)&dev->rd_msg_hdr[1]);
 		if (check_add_overflow((u32)sizeof(*meta_hdr),
 				       mei_slots2data(meta_hdr->size),
 				       &hdr_size_ext)) {
-- 
2.31.1