linux-kernel - Re: [PATCH] arm64: fix function types in COND

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Date:   Thu, 12 Sep 2019 14:11:44 +0100
From:   Will Deacon <will@...nel.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Sami Tolvanen <samitolvanen@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Kees Cook <keescook@...omium.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: fix function types in COND_SYSCALL

On Wed, Sep 11, 2019 at 04:15:46PM +0100, Mark Rutland wrote:
> On Tue, Sep 10, 2019 at 03:40:44PM -0700, Sami Tolvanen wrote:
> > Define a weak function in COND_SYSCALL instead of a weak alias to
> > sys_ni_syscall, which has an incompatible type. This fixes indirect
> > call mismatches with Control-Flow Integrity (CFI) checking.
> > 
> > Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> 
> This looks correct to me, builds fine, and I asume has been tested, so FWIW:
> 
> Acked-by: Mark Rutland <mark.rutland@....com>
> 
> In looking at this, I came to the conclusion that we can drop the ifdeffery
> around our SYSCALL_DEFINE0(), COND_SYSCALL(), and SYS_NI(), which I evidently
> cargo-culted from x86 (where the ifdeffery is actually necessary).

Curious: why is it required on x86?

> I can send a follow up for that.

Yes, please.

Will