linux-kernel - Re: [RFC 1/3] abi_spec: basic definitions of constraints, args and syscalls

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Date:   Wed, 23 Nov 2016 15:03:23 +0000
From:   alexander.levin@...izon.com
To:     Steven Rostedt <rostedt@...dmis.org>
CC:     "dvyukov@...gle.com" <dvyukov@...gle.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "scientist@...com" <scientist@...com>,
        "glider@...gle.com" <glider@...gle.com>,
        "andreyknvl@...gle.com" <andreyknvl@...gle.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "mathieu.desnoyers@...icios.com" <mathieu.desnoyers@...icios.com>,
        "daniel.vetter@...ll.ch" <daniel.vetter@...ll.ch>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 1/3] abi_spec: basic definitions of constraints, args and
 syscalls

On Mon, Nov 21, 2016 at 10:41:02AM -0500, Steven Rostedt wrote:
> On Wed, 16 Nov 2016 17:37:00 +0000
> alexander.levin@...izon.com wrote:
> 
> > This is a very simple definition of the syscall ABI we can build on. The idea
> > is to have a generic description of syscalls, their arguments and return
> > values we can use to audit the kernel's implementation vs the specs.
> > 
> > Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
> > ---
> >  include/uapi/linux/abi_spec.h | 58 +++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 58 insertions(+)
> >  create mode 100644 include/uapi/linux/abi_spec.h
> > 
> > diff --git a/include/uapi/linux/abi_spec.h b/include/uapi/linux/abi_spec.h
> > new file mode 100644
> > index 0000000..ad1a992
> > --- /dev/null
> > +++ b/include/uapi/linux/abi_spec.h
> > @@ -0,0 +1,58 @@
> > +#ifndef ABI_SPEC_H_
> > +#define ABI_SPEC_H_
> > +
> > +#include <linux/fcntl.h>
> > +#include <linux/stat.h>
> > +#define MAX_CONSTRAINTS 10
> > +#define MAX_ARGS 10
> > +
> 
> I'm curious to where you picked the number 10 from? Actually, I was
> doing some work with the syscall_get_arguments() and the max syscall
> arguments is currently set to 6. Anything greater causes a bug.

It's really just made up, but I wanted it to be higher than 6 because:

 - The "6" limit is only per-arch, so there might be something that wants
more than 6 args?
 - This should also work for ioctls in the future.

-- 

Thanks,
Sasha