linux-kernel - Re: [PATCH] Syscall arguments are unsigned long (full registers)

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Message-ID: <20160704142802.GL25121@tassilo.jf.intel.com>
Date:	Mon, 4 Jul 2016 07:28:02 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	"Tautschnig, Michael" <tautschn@...zon.co.uk>
Cc:	"x86@...nel.org" <x86@...nel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Jaswinder Singh <jaswinder@...radead.org>
Subject: Re: [PATCH] Syscall arguments are unsigned long (full registers)

On Mon, Jul 04, 2016 at 01:52:58PM +0000, Tautschnig, Michael wrote:
> All syscall arguments are passed in as types of the same byte size as
> unsigned long (width of full registers). Using a smaller type without a
> cast may result in losing bits of information. In all other instances
> apart from the ones fixed by the patch the code explicitly introduces
> type casts (using, e.g., SYSCALL_DEFINE1).
> 
> While goto-cc reported these problems at build time, it is noteworthy
> that the calling conventions specified in the System V AMD64 ABI do
> ensure that parameters 1-6 are passed via registers, thus there is no
> implied risk of misaligned stack access.

Does this actually fix anything?

It seems a big dangerous to me, potentially breaking some existing
binaries that rely on these arguments being truncated.

-Andi