Does the following constraint is convex or not? If it is not, how it can be implemented via the CVX?

\mathbf{x}^TA\mathbf{x} + C \leq(\mathbf{x}_1^T\mathbf{b})^2

where the vector \mathbf{x} = [\mathbf{x}_1^T, \mathbf{x}_2^T, ...,\mathbf{x}_N^T]^T

\mathbf{x}_n is a vector and \mathbf{x}_n\geq 0 for n=1,2,...,N

\mathbf{b}\geq 0 is a vector

C\geq 0 is a constant

Thank you in advance