linux-kernel - Re: [PATCH 2/2] arm64: use the correct function type in SYSCALL

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Date:   Fri, 3 May 2019 11:21:28 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] arm64: use the correct function type in
 SYSCALL_DEFINE0

On Wed, May 01, 2019 at 01:04:51PM -0700, Sami Tolvanen wrote:
> Although a syscall defined using SYSCALL_DEFINE0 doesn't accept
> parameters, use the correct function type to avoid indirect call
> type mismatches with Control-Flow Integrity checking.

Generally, this makes sense, but I'm not sure that this is complete.

IIUC this introduces a new type mismatch with sys_ni_syscall() in some
cases. We probably need that to use SYSCALL_DEFINE0(), and maybe have a
ksys_ni_syscall() for in-kernel wrappers.

Thanks,
Mark.

> 
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> ---
>  arch/arm64/include/asm/syscall_wrapper.h | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/syscall_wrapper.h b/arch/arm64/include/asm/syscall_wrapper.h
> index a4477e515b798..507d0ee6bc690 100644
> --- a/arch/arm64/include/asm/syscall_wrapper.h
> +++ b/arch/arm64/include/asm/syscall_wrapper.h
> @@ -30,10 +30,10 @@
>  	}										\
>  	static inline long __do_compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))
>  
> -#define COMPAT_SYSCALL_DEFINE0(sname)					\
> -	asmlinkage long __arm64_compat_sys_##sname(void);		\
> -	ALLOW_ERROR_INJECTION(__arm64_compat_sys_##sname, ERRNO);	\
> -	asmlinkage long __arm64_compat_sys_##sname(void)
> +#define COMPAT_SYSCALL_DEFINE0(sname)							\
> +	asmlinkage long __arm64_compat_sys_##sname(const struct pt_regs *__unused);	\
> +	ALLOW_ERROR_INJECTION(__arm64_compat_sys_##sname, ERRNO);			\
> +	asmlinkage long __arm64_compat_sys_##sname(const struct pt_regs *__unused)
>  
>  #define COND_SYSCALL_COMPAT(name) \
>  	cond_syscall(__arm64_compat_sys_##name);
> @@ -62,11 +62,11 @@
>  	static inline long __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))
>  
>  #ifndef SYSCALL_DEFINE0
> -#define SYSCALL_DEFINE0(sname)					\
> -	SYSCALL_METADATA(_##sname, 0);				\
> -	asmlinkage long __arm64_sys_##sname(void);		\
> -	ALLOW_ERROR_INJECTION(__arm64_sys_##sname, ERRNO);	\
> -	asmlinkage long __arm64_sys_##sname(void)
> +#define SYSCALL_DEFINE0(sname)							\
> +	SYSCALL_METADATA(_##sname, 0);						\
> +	asmlinkage long __arm64_sys_##sname(const struct pt_regs *__unused);	\
> +	ALLOW_ERROR_INJECTION(__arm64_sys_##sname, ERRNO);			\
> +	asmlinkage long __arm64_sys_##sname(const struct pt_regs *__unused)
>  #endif
>  
>  #ifndef COND_SYSCALL
> -- 
> 2.21.0.593.g511ec345e18-goog
>