linux-kernel - Re: RFD: x32 ABI system call numbers

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Message-ID: <4E5E6AC0.60000@zytor.com>
Date:	Wed, 31 Aug 2011 10:09:20 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Arnd Bergmann <arnd@...db.de>,
	Christoph Hellwig <hch@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"H.J. Lu" <hjl.tools@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Richard Kuo <rkuo@...eaurora.org>,
	Mark Salter <msalter@...hat.com>,
	Jonas Bonn <jonas@...thpole.se>,
	Tobias Klauser <tklauser@...tanz.ch>
Subject: Re: RFD: x32 ABI system call numbers

On 08/31/2011 09:46 AM, Linus Torvalds wrote:
> On Wed, Aug 31, 2011 at 9:14 AM, Arnd Bergmann <arnd@...db.de> wrote:
>>
>> * padding in struct timespec when you have a long long tv_sec and
>>  32-bit long tv_nsec. This might cause kernel stack data leakage
>>  in some kernel interfaces when they don't clear the padding.
> 
> I suspect only sane solution to this (having thought about it some
> more) is to just say "POSIX is f*^&ing wrong".
> 

Urk.  Someone had the bright idea of defining tv_nsec as "long" in the
standard, whereas tv_usec is suseconds_t.  F**** brilliant, and more
than a little bit stupid.

Logically one could work around it by having "struct timespec" contain a
padding member in the endian-appropriate place I guess, and make sure to
clear it in the kernel, but it's rather ugly.  It might have performance
advantages to doing it that way, though.

> I really think that "x32" should try to aim *VERY* hard at using the
> 64-bit system calls, and seeing itself as being a "32-bit application
> in a 64-bit world".  That's not just true for time_t (which I think
> should be 64-bit on anything new that expects to survive for any
> amount of time), but in general.

We're trying for it.  The things we're trying to avoid is to muck (too
much) with the compat layer for the mega-multiplex system calls like
ioctl.  We can't just use the 64-bit ioctl because ioctl structures
generally contain pointers.

	-hpa

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