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Date:   Wed, 15 May 2019 12:40:35 +0100
From:   Will Deacon <will.deacon@arm.com>
To:     Sami Tolvanen <samitolvanen@google.com>
Cc:     Mark Rutland <mark.rutland@arm.com>,
        Kees Cook <keescook@chromium.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 3/3] arm64: use the correct function type for
 __arm64_sys_ni_syscall
Message-ID: <20190515114035.GG24357@fuggles.cambridge.arm.com>
References: <20190503191225.6684-1-samitolvanen@google.com>
 <20190503191225.6684-4-samitolvanen@google.com>
 <20190507172512.GA35803@lakrids.cambridge.arm.com>
 <20190507183227.GA10191@google.com>
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On Tue, May 07, 2019 at 11:32:27AM -0700, Sami Tolvanen wrote:
> On Tue, May 07, 2019 at 06:25:12PM +0100, Mark Rutland wrote:
> > I strongly think that we cant to fix up the common definition in
> > kernel/sys_ni.c rather than having a point-hack in arm64. Other
> > architectures (e.g. x86, s390) will want the same for CFI, and I'd like
> > to ensure that our approached don't diverge.
> 
> s390 already has the following in arch/s390/kernel/sys_s390.c:
> 
>   SYSCALL_DEFINE0(ni_syscall)
>   {
>         return -ENOSYS;
>   }
> 
> Which, I suppose, is cleaner than calling sys_ni_syscall.
> 
> > I took a quick look, and it looks like it's messy but possible to fix
> > up the core.
> 
> OK. How would you propose fixing this?

In the absence of a patch from Mark, I'd suggest just adding a SYS_NI macro
to our asm/syscall_wrapper.h file which avoids the error injection stuff. It
doesn't preclude moving this to the core later on, but it unblocks the CFI
work.

Will