media: venus: hfi_msgs.h: Replace one-element arrays with flexible-array members

There is a regular need in the kernel to provide a way to declare having
a dynamically sized set of trailing elements in a structure. Kernel code
should always use “flexible array members”[1] for these cases. The older
style of one-element or zero-length arrays should no longer be used[2].

Use flexible-array members in struct hfi_msg_sys_property_info_pkt and
hfi_msg_session_property_info_pkt instead of one-element arrays, and
refactor the code accordingly.

Also, this helps with the ongoing efforts to enable -Warray-bounds by
fixing the following warnings:

CC [M] drivers/media/platform/qcom/venus/hfi_msgs.o
drivers/media/platform/qcom/venus/hfi_msgs.c: In function ‘hfi_sys_property_info’:
drivers/media/platform/qcom/venus/hfi_msgs.c:246:35: warning: array subscript 1 is above array bounds of ‘u32[1]’ {aka ‘unsigned int[1]’} [-Warray-bounds]
246 | if (req_bytes < 128 || !pkt->data[1] || pkt->num_properties > 1)
| ~~~~~~~~~^~~
drivers/media/platform/qcom/venus/hfi_msgs.c: In function ‘hfi_session_prop_info’:
drivers/media/platform/qcom/venus/hfi_msgs.c:342:62: warning: array subscript 1 is above array bounds of ‘u32[1]’ {aka ‘unsigned int[1]’} [-Warray-bounds]
342 | if (!req_bytes || req_bytes % sizeof(*buf_req) || !pkt->data[1])
| ~~~~~~~~~^~~

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.9/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/109

Co-developed-by: Kees Cook <[e-mail]>
Signed-off-by: Kees Cook <[e-mail]>
Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Signed-off-by: Stanimir Varbanov <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/platform/qcom/venus/hfi_msgs.c

···
 
 	req_bytes = pkt->hdr.size - sizeof(*pkt);
 
-	if (req_bytes < VER_STR_SZ || !pkt->data[1] || pkt->num_properties > 1)
+	if (req_bytes < VER_STR_SZ || !pkt->data[0] || pkt->num_properties > 1)
 		/* bad packet */
 		return;
 
-	img_ver = (u8 *)&pkt->data[1];
+	img_ver = pkt->data;
 
 	dev_dbg(dev, VDBGL "F/W version: %s\n", img_ver);
 
···
 		return;
 	}
 
-	switch (pkt->data[0]) {
+	switch (pkt->property) {
 	case HFI_PROPERTY_SYS_IMAGE_VERSION:
 		sys_get_prop_image_version(dev, pkt);
 		break;
···
 		/* bad packet */
 		return HFI_ERR_SESSION_INVALID_PARAMETER;
 
-	hfi = (struct hfi_profile_level *)&pkt->data[1];
+	hfi = (struct hfi_profile_level *)&pkt->data[0];
 	profile_level->profile = hfi->profile;
 	profile_level->level = hfi->level;
 
···
 
 	req_bytes = pkt->shdr.hdr.size - sizeof(*pkt);
 
-	if (!req_bytes || req_bytes % sizeof(*buf_req) || !pkt->data[1])
+	if (!req_bytes || req_bytes % sizeof(*buf_req) || !pkt->data[0])
 		/* bad packet */
 		return HFI_ERR_SESSION_INVALID_PARAMETER;
 
-	buf_req = (struct hfi_buffer_requirements *)&pkt->data[1];
+	buf_req = (struct hfi_buffer_requirements *)&pkt->data[0];
 	if (!buf_req)
 		return HFI_ERR_SESSION_INVALID_PARAMETER;
 
···
 		goto done;
 	}
 
-	switch (pkt->data[0]) {
+	switch (pkt->property) {
 	case HFI_PROPERTY_CONFIG_BUFFER_REQUIREMENTS:
 		memset(hprop->bufreq, 0, sizeof(hprop->bufreq));
 		error = session_get_prop_buf_req(pkt, hprop->bufreq);
···
 	case HFI_PROPERTY_CONFIG_VDEC_ENTROPY:
 		break;
 	default:
-		dev_dbg(dev, VDBGM "unknown property id:%x\n", pkt->data[0]);
+		dev_dbg(dev, VDBGM "unknown property id:%x\n", pkt->property);
 		return;
 	}
 

drivers/media/platform/qcom/venus/hfi_msgs.h

···
 struct hfi_msg_sys_property_info_pkt {
 	struct hfi_pkt_hdr hdr;
 	u32 num_properties;
-	u32 data[1];
+	u32 property;
+	u8 data[];
 };
 
 struct hfi_msg_session_load_resources_done_pkt {
···
 struct hfi_msg_session_property_info_pkt {
 	struct hfi_session_hdr_pkt shdr;
 	u32 num_properties;
-	u32 data[1];
+	u32 property;
+	u8 data[];
 };
 
 struct hfi_msg_session_release_resources_done_pkt {