EF is freely available for use in any application you want. The code and licensing is available on Github. Note however that it is only for EF6 which is the last version of EF. EF 4.3 has long been deprecated given that it was released 12 years ago. You cand find the complete version history and link to Github on their Nuget.org page.
If you have an application using EF 4.3 then it is vastly out of date and needs to be updated since that version isn't supported anymore. However if you really need to get the source code for it then the original archive is long gone. You'll need to decompile the binaries to get to the underlying code.