firmware: arm_ffa: Bound PARTITION_INFO_GET_REGS copies

The register-based PARTITION_INFO_GET path trusted the firmware-provided
indices when copying partition descriptors into the caller buffer.
Reject inconsistent counts or index progressions so the copy loop cannot
write past the allocated array.

Fixes: ba85c64 ("firmware: arm_ffa: Add support for FFA_PARTITION_INFO_GET_REGS")
Link: https://patch.msgid.link/20260428-ffa_fixes-v2-6-8595ae450034@kernel.org
(fixed cur_idx when exactly one descriptor in the first fragment)
Signed-off-by: Sudeep Holla <sudeep.holla@kernel.org>

Author: Sudeep Holla

drivers/firmware/arm_ffa/driver.c

@@ -323,22 +323,26 @@ __ffa_partition_info_get(u32 uuid0, u32 uuid1, u32 uuid2, u32 uuid3,
 #define PART_INFO_ID_MASK	GENMASK(15, 0)
 #define PART_INFO_EXEC_CXT_MASK	GENMASK(31, 16)
 #define PART_INFO_PROPS_MASK	GENMASK(63, 32)
+#define FFA_PART_INFO_GET_REGS_FIRST_REG	3
+#define FFA_PART_INFO_GET_REGS_REGS_PER_DESC	3
+#define FFA_PART_INFO_GET_REGS_MAX_DESC \
+	(((sizeof(ffa_value_t) / sizeof_field(ffa_value_t, a0)) - \
+	  FFA_PART_INFO_GET_REGS_FIRST_REG) / \
+	 FFA_PART_INFO_GET_REGS_REGS_PER_DESC)
 #define PART_INFO_ID(x)		((u16)(FIELD_GET(PART_INFO_ID_MASK, (x))))
 #define PART_INFO_EXEC_CXT(x)	((u16)(FIELD_GET(PART_INFO_EXEC_CXT_MASK, (x))))
 #define PART_INFO_PROPERTIES(x)	((u32)(FIELD_GET(PART_INFO_PROPS_MASK, (x))))
 static int
 __ffa_partition_info_get_regs(u32 uuid0, u32 uuid1, u32 uuid2, u32 uuid3,
 			      struct ffa_partition_info *buffer, int num_parts)
 {
-	u16 buf_sz, start_idx, cur_idx, count = 0, prev_idx = 0, tag = 0;
+	u16 buf_sz, start_idx = 0, cur_idx, count = 0, tag = 0;
 	struct ffa_partition_info *buf = buffer;
 	ffa_value_t partition_info;
 
 	do {
 		__le64 *regs;
-		int idx;
-
-		start_idx = prev_idx ? prev_idx + 1 : 0;
+		int idx, nr_desc, buf_idx;
 
 		invoke_ffa_fn((ffa_value_t){
 			      .a0 = FFA_PARTITION_INFO_GET_REGS,
@@ -354,15 +358,28 @@ __ffa_partition_info_get_regs(u32 uuid0, u32 uuid1, u32 uuid2, u32 uuid3,
 			count = PARTITION_COUNT(partition_info.a2);
 		if (!buffer || !num_parts) /* count only */
 			return count;
+		if (count > num_parts)
+			return -EINVAL;
 
 		cur_idx = CURRENT_INDEX(partition_info.a2);
+		if (cur_idx < start_idx || cur_idx >= count)
+			return -EINVAL;
+
+		nr_desc = cur_idx - start_idx + 1;
+		if (nr_desc > FFA_PART_INFO_GET_REGS_MAX_DESC)
+			return -EINVAL;
+
+		buf_idx = buf - buffer;
+		if (buf_idx + nr_desc > num_parts)
+			return -EINVAL;
+
 		tag = UUID_INFO_TAG(partition_info.a2);
 		buf_sz = PARTITION_INFO_SZ(partition_info.a2);
 		if (buf_sz > sizeof(*buffer))
 			buf_sz = sizeof(*buffer);
 
 		regs = (void *)&partition_info.a3;
-		for (idx = 0; idx < cur_idx - start_idx + 1; idx++, buf++) {
+		for (idx = 0; idx < nr_desc; idx++, buf++) {
 			union {
 				uuid_t uuid;
 				u64 regs[2];
@@ -380,7 +397,7 @@ __ffa_partition_info_get_regs(u32 uuid0, u32 uuid1, u32 uuid2, u32 uuid3,
 			uuid_copy(&buf->uuid, &uuid_regs.uuid);
 			regs += 3;
 		}
-		prev_idx = cur_idx;
+		start_idx = cur_idx + 1;
 
 	} while (cur_idx < (count - 1));