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Re: The 64-bit version of __access_ok is broken.

To: Ralf Baechle <ralf@linux-mips.org>
Subject: Re: The 64-bit version of __access_ok is broken.
From: Dominic Sweetman <dom@algor.co.uk>
Date: Mon, 9 Dec 2002 11:54:20 +0000
Cc: Carsten Langgaard <carstenl@mips.com>, Dominic Sweetman <dom@mips.com>, chris@mips.com, kevink@mips.com, linux-mips@linux-mips.org
In-reply-to: <3DF4629B.F377F711@mips.com>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <3DEF7087.B6DEA7EC@mips.com> <20021209051845.A31939@linux-mips.org> <3DF4629B.F377F711@mips.com>
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> > > The __access_ok macro in include/asm-mips64/uaccess.h and the
> > > check_axs macro in arch/mips64/kernel/unaligned.c ... is a copy
> > > from the 32-bit kernel...
> > >
> > > The area between USEG (XUSEG) and KSEG0 will in 64-bit
> > > addressing mode generate an address error, if accessed.

I'd like to be clear about the consequences of this.  Presumably the
'access_ok()' macro is used to check addresses which were (originally)
provided by a user program's system call.

Carsten, are you saying that if such an address is set to say 2**41 in
a CPU supporting 40-bit user virtual addresses, that the kernel will
crash?

If so, that seems to require a fix, even if we don't know a very
efficient one.  But perhaps any problem is a bit more subtle than
that?

-- 
Dominic Sweetman
MIPS Technologies
The Fruit Farm, Ely Road, Chittering, CAMBS CB5 9PH, ENGLAND
phone +44 1223 706205/fax +44 1223 706250/swbrd +44 1223 706200
http://www.algor.co.uk



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