firmware: arm_ffa: Avoid string-fortify warning caused by memcpy()

Copying from a 144 byte structure arm_smccc_1_2_regs at an offset of 32
into an 112 byte struct ffa_send_direct_data2 causes a compile-time warning:

 | In file included from drivers/firmware/arm_ffa/driver.c:25:
 | In function 'fortify_memcpy_chk',
 |    inlined from 'ffa_msg_send_direct_req2' at drivers/firmware/arm_ffa/driver.c:504:3:
 | include/linux/fortify-string.h:580:4: warning: call to '__read_overflow2_field'
 | 	declared with 'warning' attribute: detected read beyond size of field
 | 	(2nd parameter); maybe use struct_group()? [-Wattribute-warning]
 |                         __read_overflow2_field(q_size_field, size);

Fix it by not passing a plain buffer to memcpy() to avoid the overflow
warning.

Fixes: aaef3bc ("firmware: arm_ffa: Add support for FFA_MSG_SEND_DIRECT_{REQ,RESP}2")
Signed-off-by: Gavin Shan <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Sudeep Holla <[email protected]>

Author: Gavin Shan

drivers/firmware/arm_ffa/driver.c

@@ -501,7 +501,7 @@ static int ffa_msg_send_direct_req2(u16 src_id, u16 dst_id, const uuid_t *uuid,
 		return ffa_to_linux_errno((int)ret.a2);
 
 	if (ret.a0 == FFA_MSG_SEND_DIRECT_RESP2) {
-		memcpy(data, &ret.a4, sizeof(*data));
+		memcpy(data, (void *)&ret + offsetof(ffa_value_t, a4), sizeof(*data));
 		return 0;
 	}