linux-kernel - Re: [PATCH 1/4] arch/arm: add syscall_get

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Message-ID: <20121105132907.GL3351@mudshark.cambridge.arm.com>
Date:	Mon, 5 Nov 2012 13:29:07 +0000
From:	Will Deacon <will.deacon@....com>
To:	Kees Cook <keescook@...omium.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>,
	Will Drewry <wad@...omium.org>,
	Geremy Condra <gcondra@...gle.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Catalin Marinas <Catalin.Marinas@....com>
Subject: Re: [PATCH 1/4] arch/arm: add syscall_get_arch

On Fri, Nov 02, 2012 at 12:14:57AM +0000, Kees Cook wrote:
> From: Will Drewry <wad@...omium.org>
> 
> Provide an ARM implementation of syscall_get_arch. This is a pre-requisite
> for CONFIG_HAVE_ARCH_SECCOMP_FILTER.
> 
> Signed-off-by: Will Drewry <wad@...omium.org>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  arch/arm/include/asm/syscall.h |   13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/arch/arm/include/asm/syscall.h b/arch/arm/include/asm/syscall.h
> index 9fdded6..803f433 100644
> --- a/arch/arm/include/asm/syscall.h
> +++ b/arch/arm/include/asm/syscall.h
> @@ -7,6 +7,8 @@
>  #ifndef _ASM_ARM_SYSCALL_H
>  #define _ASM_ARM_SYSCALL_H
>  
> +#include <linux/audit.h> /* for AUDIT_ARCH_* */
> +#include <linux/elf.h> /* for ELF_EM */
>  #include <linux/err.h>
>  #include <linux/sched.h>
>  
> @@ -95,4 +97,15 @@ static inline void syscall_set_arguments(struct task_struct *task,
>  	memcpy(&regs->ARM_r0 + i, args, n * sizeof(args[0]));
>  }
>  
> +static inline int syscall_get_arch(struct task_struct *task,
> +				   struct pt_regs *regs)
> +{
> +	/* ARM tasks don't change audit architectures on the fly. */
> +#ifdef __ARMEB__
> +	return AUDIT_ARCH_ARMEB;
> +#else
> +	return AUDIT_ARCH_ARM;
> +#endif
> +}

I think you can just use AUDIT_ARCH_ARM unconditionally here as the syscall
ABI is not related to the endianness of the CPU. I believe AUDIT_ARCH_ARMEB
was added accidentally because somebody incorrectly thought the -EB suffix
signified EABI.

If it wasn't in a user-header I'd be all for deleting the old definition...

Will
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