linux-kernel - Re: [PATCH 3/4] x86: use the correct function type for sys_ni

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Message-ID: <20190916204315.vtvlddghswbwlfkg@willie-the-truck>
Date:   Mon, 16 Sep 2019 21:43:16 +0100
From:   Will Deacon <will@...nel.org>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Sami Tolvanen <samitolvanen@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Kees Cook <keescook@...omium.org>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, will.deacon@....com,
        mark.rutland@....com
Subject: Re: [PATCH 3/4] x86: use the correct function type for sys_ni_syscall

On Fri, Sep 13, 2019 at 05:27:40PM -0700, Andy Lutomirski wrote:
> > On Sep 13, 2019, at 4:26 PM, Sami Tolvanen <samitolvanen@...gle.com> wrote:
> >> On Fri, Sep 13, 2019 at 3:45 PM Andy Lutomirski <luto@...nel.org> wrote:
> >> Should this be SYSCALL_DEFINE0?
> > 
> > It can be, and that would also fix the issue. However, it does result
> > in unnecessary error injection to be hooked up here, which is why
> > arm64 preferred to avoid the macro when I fixed it there. S390 uses
> > SYSCALL_DEFINE0 for this though and since sys_ni_syscall always
> > returns -ENOSYS, it shouldn't be a huge problem. Thoughts?
> > 
> 
> I don’t see why all syscalls except these  few should have error injection
> hooked up.  It’s also IMO nicer from a maintenance perspective to have all
> syscalls use the same macros.
> 
> Will, is there something I’m missing?

There was a reasonable request from Mark (CC'd) not to allow error injection
for unimplemented system calls, so that's why we took the approach that we
did. There was also a vague plan to fix this for everybody [1] but evidently
nobody found the time :(

Will

[1] https://lore.kernel.org/lkml/20190524215821.GA37129@google.com/T/#m6519b2aad06d8c384de1f55256f08687c83d8796