Not the case. Some VDSOs just forward to regular system calls. Try clock_gettime with CLOCK_BOOTTIME sometime. (I need to send a patch to fix this. Maybe over Christmas.)
Requiring that every system call go through a VDSO would be great because it would give us a "hook" for changing system behavior before entering the kernel, which is a good thing, because in the age of speculative execution mitigations, entering the kernel is expensive, just like in the days of yore.
Requiring that every system call go through a VDSO would be great because it would give us a "hook" for changing system behavior before entering the kernel, which is a good thing, because in the age of speculative execution mitigations, entering the kernel is expensive, just like in the days of yore.