linux-kernel - Re: [PATCH v2] x86: Preserve iopl on fork and execve

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Message-ID: <CADyApD3Kom234GhvNdxTiF8xpUdqp9cLp8TuGLTkrQ=Z3ESkfg@mail.gmail.com>
Date:	Tue, 12 May 2015 08:24:38 -0700
From:	Arjan van de Ven <arjanvandeven@...il.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Alex Henrie <alexhenrie24@...il.com>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Kees Cook <keescook@...omium.org>,
	"H . Peter Anvin" <hpa@...or.com>, Doug Johnson <dougvj@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Tyler Hicks <tyhicks@...onical.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	LKML <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arjan van de Ven <arjan@...radead.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Brian Gerst <brgerst@...il.com>
Subject: Re: [PATCH v2] x86: Preserve iopl on fork and execve

On Mon, May 11, 2015 at 11:40 PM, Ingo Molnar <mingo@...nel.org> wrote:
>  - Nothing actually broke that people cared about in the last 2.5
>    years, thus this might be one of the (very very rare) cases where
>    preserving a breakage is the right thing to do.


>  - These syscalls are rarely used, and we could as well insist that
>    every new context should have the permissions to (re-)acquire them
>    and should actively seek them - instead of inheriting it to shells
>    via system(), etc. The best strategy with dangerous APIs is to make
>    it really, really explicit when they are used.

since nothing really broke and its a "nasty either way" regression
wise, picking the more secure path looks the most sane.

the most likely impact path is in the X world, where X normally gets
iopl type permissions (even thought it doesn't need
them anymore nowadays).. reverting this behavior would give all the
processes X spawns off those perms as well...

also the interesting question is:
can a process give up these perms?
otherwise it becomes a "once given, never gotten rid of" hell hole.
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