linux-kernel - Re: + espfix-code-cleanup.patch added to -mm tree

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Date:	Wed, 02 Aug 2006 21:12:21 +0400
From:	Stas Sergeev <stsp@...et.ru>
To:	Zachary Amsden <zach@...are.com>
Cc:	Linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: + espfix-code-cleanup.patch added to -mm tree

Hi,

Zachary Amsden wrote:
> You need to get a #GP or #NP on the faulting iret.  Several ways to do 
> that -
I do that much simpler - I provoke a SIGSEGV and in a signal handler
I put the wrong value to scp->cs or scp->ss, and that makes iret to fault.

> iret faults, but doesn't pop the user return frame.
But does it push the kernel frame after it or not?
If not - I don't understand how we go to a fixup.
If yes - I don't understand how the user's frame gets
accessed later, as it is above the kernel's frame.

>> safe limit is regs->esp + THREAD_SIZE*2... Well, may just I not do 
>> that please? :)
>> For what, btw? There are no such a things for __KERNEL_DS or anything, so
>> I just don't see the necessity.
> It helps track down any bugs that could leak through otherwise and 
> corrupt random memory.
I think regs->esp + THREAD_SIZE*2 is already very permissive,
and I'd like to avoid messing with granularity. So unless you
really insist, I'll better not do that. :)

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