From: Philipp Kohlbecher <pk031698@uni-greifswald.de>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Dave Jones <davej@codemonkey.org.uk>,
Arnd Bergmann <arnd@arndb.de>,
linux-kernel@vger.kernel.org, linux-assembly@vger.kernel.org
Subject: Re: [PATCH 2.6.21.1] i386: save registers before intra-privilege syscall
Date: Mon, 21 May 2007 12:48:42 +0200 [thread overview]
Message-ID: <4651790A.2050703@uni-greifswald.de> (raw)
In-Reply-To: <464E2B97.9040205@zytor.com>
H. Peter Anvin wrote:
> Sticking kernel mode values in those fields would add no value, except
> as a poison (since %ss == KERNEL_DS and would cause a #GP(0) if it ever
> reached IRET.) If anything, those fields should be pushed as zero or
> some other poison bits. That would be slightly better than what's there
> now, which is whatever garbage happens to be on the stack. Pushing the
> kernel SS:ESP is just plain wrong (not to mention that the way you do it
> doesn't even produce the right value for ESP -- you'd have to save away
> ESP before you push SS.)
That's true. The xss and esp fields of the pt_regs struct always contain
either garbage (for interrupts occuring while in kernel mode) or
user-mode values (for interrupts occuring while in user mode).
So, filling these fields with kernel-mode values indeed doesn't make
much sense.
Allocating space on the stack and poisoning those values would make
sense, though, so I will modify the patch accordingly and resend it.
Thank you for your feedback!
- Philipp Kohlbecher
prev parent reply other threads:[~2007-05-21 10:48 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-05-17 22:06 [PATCH 2.6.21.1] i386: save registers before intra-privilege syscall Philipp Kohlbecher
2007-05-17 22:16 ` H. Peter Anvin
2007-05-17 23:27 ` Philipp Kohlbecher
2007-05-17 23:33 ` H. Peter Anvin
2007-05-18 8:32 ` Philipp Kohlbecher
2007-05-18 22:41 ` H. Peter Anvin
2007-05-18 23:08 ` H. Peter Anvin
2007-05-21 10:48 ` Philipp Kohlbecher [this message]
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