linux-kernel - Re: [PATCH v1 6/8] x86/entry/clearregs: Add number of arguments to syscall tables

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Date:   Tue, 9 Jan 2018 20:37:51 -0800
From:   Andi Kleen <ak@...ux.intel.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Andi Kleen <andi@...stfloor.org>, tglx@...utronix.de,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, dwmw@...zon.co.uk, pjt@...gle.com,
        luto@...nel.org, peterz@...radead.org, thomas.lendacky@....com,
        tim.c.chen@...ux.intel.com, gregkh@...ux-foundation.org,
        dave.hansen@...el.com, jikos@...nel.org
Subject: Re: [PATCH v1 6/8] x86/entry/clearregs: Add number of arguments to
 syscall tables

On Tue, Jan 09, 2018 at 05:26:43PM -0800, Andy Lutomirski wrote:
> 
> 
> > On Jan 9, 2018, at 5:03 PM, Andi Kleen <andi@...stfloor.org> wrote:
> > 
> > From: Andi Kleen <ak@...ux.intel.com>
> > 
> > In order to sanitize the system call arguments properly
> > we need to know the number of syscall arguments for each
> > syscall. Add a new column to the 32bit and 64bit syscall
> > tables to list the number of arguments.
> > 
> 
> Surely we can do this in the SYSCALL_DEFINE macros.  Or at least statically check it.

Possibly. The assembler would be much uglier as inline assembler though.
And adding the number shouldn't be a big burden when adding a system call.

I don't know how to check statically.

> 
> Also, what attack are we protecting against anyway?

There's no specific attack here.

But the idea is to make it harder to inject values into the kernel to abuse
with speculation.

-Andi