linux-kernel - Re: [PATCH] seccomp: Use current_pt

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Message-ID: <202008240929.8DDED2B90@keescook>
Date:   Mon, 24 Aug 2020 09:34:27 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Denis Efremov <efremov@...ux.com>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] seccomp: Use current_pt_regs()

On Mon, Aug 24, 2020 at 03:59:21PM +0300, Denis Efremov wrote:
> Modify seccomp_do_user_notification(), __seccomp_filter(),
> __secure_computing() to use current_pt_regs().

This looks okay. It seems some architectures have a separate
define for current_pt_regs(), though it's overlapped directly with
task_pt_regs(). I'm curious what the benefit of the change is?

-Kees

> 
> Signed-off-by: Denis Efremov <efremov@...ux.com>
> ---
>  kernel/seccomp.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index 3ee59ce0a323..dc4eaa1d6002 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -910,7 +910,7 @@ static int seccomp_do_user_notification(int this_syscall,
>  	if (flags & SECCOMP_USER_NOTIF_FLAG_CONTINUE)
>  		return 0;
>  
> -	syscall_set_return_value(current, task_pt_regs(current),
> +	syscall_set_return_value(current, current_pt_regs(),
>  				 err, ret);
>  	return -1;
>  }
> @@ -943,13 +943,13 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
>  		/* Set low-order bits as an errno, capped at MAX_ERRNO. */
>  		if (data > MAX_ERRNO)
>  			data = MAX_ERRNO;
> -		syscall_set_return_value(current, task_pt_regs(current),
> +		syscall_set_return_value(current, current_pt_regs(),
>  					 -data, 0);
>  		goto skip;
>  
>  	case SECCOMP_RET_TRAP:
>  		/* Show the handler the original registers. */
> -		syscall_rollback(current, task_pt_regs(current));
> +		syscall_rollback(current, current_pt_regs());
>  		/* Let the filter pass back 16 bits of data. */
>  		seccomp_send_sigsys(this_syscall, data);
>  		goto skip;
> @@ -962,7 +962,7 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
>  		/* ENOSYS these calls if there is no tracer attached. */
>  		if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) {
>  			syscall_set_return_value(current,
> -						 task_pt_regs(current),
> +						 current_pt_regs(),
>  						 -ENOSYS, 0);
>  			goto skip;
>  		}
> @@ -982,7 +982,7 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
>  		if (fatal_signal_pending(current))
>  			goto skip;
>  		/* Check if the tracer forced the syscall to be skipped. */
> -		this_syscall = syscall_get_nr(current, task_pt_regs(current));
> +		this_syscall = syscall_get_nr(current, current_pt_regs());
>  		if (this_syscall < 0)
>  			goto skip;
>  
> @@ -1025,7 +1025,7 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
>  			kernel_siginfo_t info;
>  
>  			/* Show the original registers in the dump. */
> -			syscall_rollback(current, task_pt_regs(current));
> +			syscall_rollback(current, current_pt_regs());
>  			/* Trigger a manual coredump since do_exit skips it. */
>  			seccomp_init_siginfo(&info, this_syscall, data);
>  			do_coredump(&info);
> @@ -1060,7 +1060,7 @@ int __secure_computing(const struct seccomp_data *sd)
>  		return 0;
>  
>  	this_syscall = sd ? sd->nr :
> -		syscall_get_nr(current, task_pt_regs(current));
> +		syscall_get_nr(current, current_pt_regs());
>  
>  	switch (mode) {
>  	case SECCOMP_MODE_STRICT:
> -- 
> 2.26.2
> 

-- 
Kees Cook