* The vDSO is mapped at a fixed address in every process, making return-to-libc-style attacks easy. This doesn't seem to be necessary, though, since it's a virtual dynamic shared object, and you can ASLR it just like you can ASLR any other dynamic library. Just tell the program where you put it.

* The vDSO (or at least the vsyscall page, not sure if this is still true) includes a syscall instruction, making it a juicy target for return-to-libc-style attacks. But for gettimeofday() you don't need that. Just include the instruction to read some dedicated read-only page from memory-mapped timer hardware, or run RDTSC, or whatever, and make your ABI such that it permits the vDSO call to fail and regular libc code might have to make a real syscall if it does. Or that the vDSO isn't guaranteed to be present, and is missing if hardware support is missing.

Any further information here?

The idea is just having a special page that is mapped as read-only in userspace and kernel writable. If it's correctly implemented, it should be safe.