linux-kernel - Re: [PATCHv2 1/1] Documentation: describe how to add a system call

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Message-ID: <20150730190434.GD16452@x>
Date:	Thu, 30 Jul 2015 12:04:35 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	Kees Cook <keescook@...omium.org>
Cc:	David Drysdale <drysdale@...gle.com>,
	Ingo Molnar <mingo@...nel.org>,
	Linux API <linux-api@...r.kernel.org>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	Shuah Khan <shuahkh@....samsung.com>,
	Jonathan Corbet <corbet@....net>,
	Eric B Munson <emunson@...mai.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Oleg Nesterov <oleg@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Al Viro <viro@...iv.linux.org.uk>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Peter Zijlstra <peterz@...radead.org>,
	Vivek Goyal <vgoyal@...hat.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	David Herrmann <dh.herrmann@...il.com>,
	Theodore Ts'o <tytso@....edu>,
	Milosz Tanski <milosz@...in.com>, Fam Zheng <famz@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCHv2 1/1] Documentation: describe how to add a system call

On Thu, Jul 30, 2015 at 11:21:54AM -0700, Kees Cook wrote:
> I like this, it's a good description of both options. I'm still biased
> about the approach: I prefer flags, since pointers to user structures
> complicate syscall filtering. ;)

Seems like we should do two things to make that easier:

1) Create a standardized kernel mechanism for parameter-struct handling,
   implementing the recommendations mentioned here.
2) Integrate into that mechanism a way to filter the resulting parameter
   struct with BPF *after* it has been copied to kernel space (and thus
   can no longer be tampered with).

- Josh Triplett
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