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Date: Sun, 22 Dec 2002 15:32:29 +0000
From: Jamie Lokier <lk@tantalophile.demon.co.uk>
To: Ingo Molnar <mingo@elte.hu>
Cc: Linus Torvalds <torvalds@transmeta.com>,
       Ulrich Drepper <drepper@redhat.com>, bart@etpmod.phys.tue.nl,
       davej@codemonkey.org.uk, hpa@transmeta.com, terje.eggestad@scali.com,
       matti.aarnio@zmailer.org, hugh@veritas.com,
       linux-kernel@vger.kernel.org
Subject: Re: Intel P6 vs P7 system call performance
Message-ID: <20021222153229.GA30269@bjl1.asuk.net>
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Ingo Molnar wrote:
> and i'm 100% sure the more robust eflags saving will also avoid security
> holes. The amount of security-relevant complexity that comes from all the
> x86 features [and their combinations] is amazing.

Userspace can skip the "popfl" with a well-timed signal.  If the
"sysexit" path leaves the kernel with an unsafe eflags, that will
propagate into the signal handler.

AFAICT, one of these is required:

	1. eflags must be safe before leaving kernel space, or
	2. setup_sigcontext() must clean it up (it already does clear TF).

-- Jamie
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