# Re: \[PATCH v6 6/9\] kernel: entry: Support Syscall User Dispatch for common syscall entry

- From: peterz@infradead.org
- Date: 2020-09-11 09:46:47 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2020/09/6101778
- Thread: https://ratatoskr.run/linux-api/2020/09/6094737/t.md

```text
On Fri, Sep 04, 2020 at 04:31:44PM -0400, Gabriel Krisman Bertazi wrote:
> Syscall User Dispatch (SUD) must take precedence over seccomp, since the
> use case is emulation (it can be invoked with a different ABI) such that
> seccomp filtering by syscall number doesn't make sense in the first
> place.  In addition, either the syscall is dispatched back to userspace,
> in which case there is no resource for seccomp to protect, or the
> syscall will be executed, and seccomp will execute next.
> 
> Regarding ptrace, I experimented with before and after, and while the
> same ABI argument applies, I felt it was easier to debug if I let ptrace
> happen for syscalls that are dispatched back to userspace.  In addition,
> doing it after ptrace makes the code in syscall_exit_work slightly
> simpler, since it doesn't require special handling for this feature.

I think I'm with Andy that this should be before ptrace(). ptrace()
users will attempt to interpret things like they're regular syscalls,
and that's definitely not the case.
```