linux-kernel - Re: [RESEND PATCH v4 2/2] arm64: Add seccomp support

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Date:	Wed, 9 Jul 2014 12:12:39 +0100
From:	Will Deacon <will.deacon@....com>
To:	AKASHI Takahiro <takahiro.akashi@...aro.org>
Cc:	"wad@...omium.org" <wad@...omium.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"dsaxena@...aro.org" <dsaxena@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND PATCH v4 2/2] arm64: Add seccomp support

Hi Akashi,

On Fri, Jul 04, 2014 at 08:31:55AM +0100, AKASHI Takahiro wrote:
> secure_computing() should always be called first in syscall_trace_enter().
> If it returns non-zero, we should stop further handling. Then that system
> call may eventually fail, be trapped or the process itself be killed
> depending on loaded rules.
> In this case, syscall_trace_enter() returns a dedicated value in order to
> skip a normal syscall table lookup because a seccomp rule may have already
> overridden errno.

[...]

> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
> index 70526cf..baab5fc 100644
> --- a/arch/arm64/kernel/ptrace.c
> +++ b/arch/arm64/kernel/ptrace.c
> @@ -21,12 +21,14 @@
>  
>  #include <linux/audit.h>
>  #include <linux/compat.h>
> +#include <linux/errno.h>
>  #include <linux/kernel.h>
>  #include <linux/sched.h>
>  #include <linux/mm.h>
>  #include <linux/smp.h>
>  #include <linux/ptrace.h>
>  #include <linux/user.h>
> +#include <linux/seccomp.h>
>  #include <linux/security.h>
>  #include <linux/init.h>
>  #include <linux/signal.h>
> @@ -1109,6 +1111,10 @@ static void tracehook_report_syscall(struct pt_regs *regs,
>  
>  asmlinkage int syscall_trace_enter(struct pt_regs *regs)
>  {
> +	if (secure_computing(regs->syscallno) == -1)
> +		/* seccomp failures shouldn't expose any additional code. */
> +		return -EPERM;
> +
>  	if (test_thread_flag(TIF_SYSCALL_TRACE))
>  		tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);

We return regs->syscallno immediately after this, so we have the same issue
that Kees identified for arch/arm/. Did you follow the discussion I had with
Andy?

Will
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