Re: [PATCH v4 1/2] kernel: Implement selective syscall userspace redirection

[Will Deacon]

On Mon, Jul 20, 2020 at 11:23:13AM +0200, Thomas Gleixner wrote:
> Andy Lutomirski <luto@xxxxxxxxxx> writes:
> > On Thu, Jul 16, 2020 at 12:31 PM Gabriel Krisman Bertazi
> > <krisman@xxxxxxxxxxxxx> wrote:
> > The amount of syscall entry wiring that arches need to do is IMO
> > already a bit out of hand.  Should we instead rename TIF_SECCOMP to
> > TIF_SYSCALL_INTERCEPTION and have one generic callback that handles
> > seccomp and this new thing?
> 
> The right way to go is to consolidate all the stupidly different
> entry/exit work handling implementations and have exactly one in generic
> code, i.e. what I posted a few days ago.
> 
> Then we can make new features only available in the generic version by
> hiding the new functionality in the core code and not exposing the
> functions to architecture implementations.
> 
> Making it easy for architectures to keep their own variant forever just
> proliferates the mess we have right now.

Couldn't agree more. We recently added PTRACE_SYSEMU to arm64 and I deeply
regret doing that now that yet another way to rewrite the syscall number
has come along. I only just untangled some of the mess in our entry code
for that, so I can't say I'm looking forward to opening it right back up
to support this new feature. Much better to do it in the core code instead.

Will