If, instead, as on OpenBSD, the kernel enforced the rule that all system calls had to go through libc (or perhaps a big ntdll.dll-like VDSO), then the whole problem the linked article tries in vain to solve would disappear. If you wanted to hook a system call, you'd just change the libc/VDSO dispatch. No need to rewrite any instructions.
If I were Linus, I'd make a new rule: starting today, all new system calls must go through VDSO. No exceptions. SYSCALL from anywhere else? SIGKILL.
This way, you can just LD_PRELOAD in front of the VDSO and system call interception in userspace Just Works.
This model has always been a trade-off. It has downsides, but it also has upsides, including an immense boost in flexibility; decoupling from any particular userspace is useful.
> This way, you can just LD_PRELOAD in front of the VDSO and system call interception in userspace Just Works.
Can you LD_PRELOAD in front of the vDSO? I was under the (possibly mistaken) impression that the kernel injects it directly.
Which makes containers crap on Windows and *BSD as they have to run the currect libc or equivalent. Thus you need to build a different container per OS version which sucks compared to Linux.
Or, you know, just propose your idea to him