RSB
I've only had a short think about this, but it strikes me that the main problem here is that the contents of the Return Stack Buffer persists across context switches.
If whatever OS kernel is being used invalidated the RSB when context switching between different process/threads, then this may affect performance, but should prevent this type of leak between processes. Any performance impact would only be when a process is re-scheduled.
Switching to kernel mode (a system call) would be a bit more problematic, as system calls happen frequently. You would not really want to invalidate the RSB on every syscall, but I would have thought that there should be something that the syscall interface could do to sanitize the RSB it inherits from the process. But the separation of the kernel and process address spaces in the Meltdown fixes should really limit the damage.
As I say, I've not read the full papers yet, so there may be something I haven't considered.
Biting the hand that feeds IT
