linux-kernel - Re: [RFC] x86: restrict pid namespaces to 32 or 64 bit syscalls

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Date:	Mon, 15 Aug 2011 11:59:56 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Solar Designer <solar@...nwall.com>
CC:	Andi Kleen <andi@...stfloor.org>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	James Morris <jmorris@...ei.org>,
	kernel-hardening@...ts.openwall.com, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	Will Drewry <wad@...omium.org>
Subject: Re: [RFC] x86: restrict pid namespaces to 32 or 64 bit syscalls

On 08/15/2011 11:51 AM, Solar Designer wrote:
> I agree with you that i386 vs x86-64 vs x32 is one axis and syscall
> number is another axis.

They are not.  ABI is ONE SUBSET OF SYSCALL NUMBERS.

> Per-syscall restrictions are also useful, but primarily at a different
> level - I'd expect them to be used in specific programs, such as Chrome
> and vsftpd.  Those programs may also want to limit themselves to a
> certain type of syscalls (that is, on the i386 vs x86-64 vs x32 axis),
> thereby making use of both features at once.  Or they might even have to
> do that, depending on how we implement the syscall restrictions.
> 
> Per your suggestion, if I understand correctly, any task that wants to
> restrict itself on the i386 vs x86-64 vs x32 axis will have TIF_SECCOMP
> set and will incur calls into __secure_computing().  This is unnecessary
> overhead for the case when we have a restriction over this axis only,
> without per-syscall restrictions.  Vasiliy's patch avoids such overhead.

There is really no bloody difference between i386 vs x86-64 and, say,
sys_oldstat versus sys_stat, or anything else along those lines.
Putting in a bunch of ad hoc facilities because of semi-plausible
performance wins rather than building a sane filtering facility which
can be optimized as a single path is ridiculous.

	-hpa
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