On Fri, Mar 16, 2018 at 03:55:04PM -0700, Howard McLauchlan wrote:
> On 03/13/2018 04:56 PM, Andy Lutomirski wrote:
> > On Tue, Mar 13, 2018 at 11:16 PM, Howard McLauchlan <[email protected]>
> > wrote:
> >> Error injection is a useful mechanism to fail arbitrary kernel
> >> functions. However, it is often hard to guarantee an error propagates
> >> appropriately to user space programs. By injecting into syscalls, we can
> >> return arbitrary values to user space directly; this increases
> >> flexibility and robustness in testing, allowing us to test user space
> >> error paths effectively.
> >
> > Temporary NAK IMO. Specifically:
> >
> >> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> >> index a78186d826d7..e8c6d63ace78 100644
> >> --- a/include/linux/syscalls.h
> >> +++ b/include/linux/syscalls.h
> >> @@ -191,6 +191,8 @@ static inline int is_syscall_trace_event(struct
> >> trace_event_call *tp_event)
> >>
> >> #define SYSCALL_DEFINE0(sname) \
> >> SYSCALL_METADATA(_##sname, 0); \
> >> + asmlinkage long sys_##sname(void); \
> >> + ALLOW_ERROR_INJECTION(sys_##sname, ERRNO); \
> >
> > sys_xyz() is not just the syscall itself; it's also a helper that's
> > used for entirely silly reasons by various bits of kernel code for
> > quite a few syscalls. Fortunately, Dominik has patches to fix that,
> > and Linus is even considering pulling them for 4.16. This patch will
> > most likely conflict with the final result of Dominik's series.
> >
> > Can you and Dominik coordinate a bit to get this patch or its
> > equivalent landed on top of Dominik's work? It might make sense for
> > Dominik to just add this patch to his series so it can land with the
> > rest of it. Dominik, Ingo, what do you think?
> >
> > --Andy
> >
>
> Dominik,
>
> This patch applies cleanly on top of your patch series. Is there anything
> you'd need from me to get this in on top of your work?
Howard,
would this form part of the kernel<->userspace interface and therefore needs
to be kept stable? If so, this patch should wait until the arch-specific
syscall calling convention is agreed upon.
Moreover, the patches I sent out already do not cover all syscalls yet.
Until all in-kernel users of sys_*() are gone (or at least outside arch/),
I'd prefer to postpone this patch.
Thanks,
Dominik
