Without seeing your code It's hard to say exactly where the issue is. The shader code you posted looks alright. From the images you have posted I've seen that issue before when the shadow frustum hasn't been built correctly and/or the frustum is missing a transform into light space. Maybe also look over the matrices you're passing into the shader to make sure they are correct.

Without seeing your code It's hard to say exactly where the issue is. The shader code you posted looks alright. From the images you have posted I've seen that issue before when the shadow frustum hasn't been built correctly and/or the frustum is missing a transform into light space.