linux-kernel - Re: [PSEUDOPATCH] rename is_compat

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Date:	Mon, 7 Dec 2015 21:52:31 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Ingo Molnar <mingo@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-arch <linux-arch@...r.kernel.org>,
	David Miller <davem@...emloft.net>
Subject: Re: [PSEUDOPATCH] rename is_compat_task

On Mon, Dec 7, 2015 at 9:15 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
> On Tue, Dec 08, 2015 at 06:01:48AM +0100, Ingo Molnar wrote:
>
>> Hm, so if Sparc has no notion of compat-ness of the system call then how does it
>> implement runtime compat checks, such as AUDIT_ARCH et al?
>
> Badly.  Things like compat_sys_ioctl() vs. ioctl() work (we use different
> arrays of function pointers in 32bit and 64bit traps), but anything
> dynamic assumes that things match the task.  Not that we had a lot of
> such dynamic checks, actually...

I wouldn't take x86 as a shining example of how to do this, but it
does mostly work.  In 4.4, it's not even all that messy, modulo a
bunch of checks that check the wrong condition (hence, in part, this
proposal).

--Andy
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