Treat nested std::arrays as a single flat array with chained .data()

Let's say I have this little fixed-dimension matrix class:

template<size_t M, size_t N>
struct MatMN { 
  std::array<std::array<double, N>, M> rows;
  double* begin() { return rows.data()->data(); } //The scary part
  double* end() { return begin() + M*N; }
  //const iterators, etc.
};

and instead of using nested loops, I implement scalar multiplication (also equality testing, binary de/serialization, etc.) like so:

template<size_t M, size_t N>
MatMN<M, N> operator*(double scalar, MatMN<M, N> mat) {
  for (double& x_ : mat) { x_ *= scalar; }
  return mat;
}

Is it actually okay to treat nested std::arrays as a single flat C-style array by using .data()->data()?

Am I at risk of some strict-aliasing issue? Or maybe unexpected struct padding at the end of individual std::arrays (i.e. between matrix rows)? So far it's worked fine for me (with GCC), but I know that doesn't mean much in C++.