From: Ralf Baechle <ralf@linux-mips.org>
To: Dimitri Torfs <dimitri@sonycom.com>
Cc: linux-mips@linux-mips.org
Subject: Re: access_ok and CONFIG_MIPS32 for 2.6
Date: Fri, 2 Jan 2004 20:44:03 +0100 [thread overview]
Message-ID: <20040102194403.GB31092@linux-mips.org> (raw)
In-Reply-To: <20040102145941.GA13426@sonycom.com>
On Fri, Jan 02, 2004 at 03:59:41PM +0100, Dimitri Torfs wrote:
> the mask used in access_ok to check the validity of an address range
> evaluates to -TASK_SIZE for user processes. In case of
> CONFIG_MIPS32, TASK_SIZE is defined as 0x7fff8000UL, so -TASK_SIZE
> evaluates to 0x80008000, making access_ok return false for all
> addresses with bit 15 and 31 set. Surely the mask should be 0x80000000.
>
> Does anybody know why TASK_SIZE is set to 0x7fff8000 and not
> 0x80000000 ?
There is a weird special case were 32-bit code running on a 64-bit kernel
with c0_status.ux set will behave differently than on a 32-bit processor
or with c0_status.ux clear. The workaround for 64-bit kernels is to
leave the top 32kB of the 2GB user virtual address space unused. For
sake of symmetry we do this on both 32-bit and 64-bit kernels.
Ralf
next prev parent reply other threads:[~2004-01-02 19:44 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-01-02 14:59 access_ok and CONFIG_MIPS32 for 2.6 Dimitri Torfs
2004-01-02 19:44 ` Ralf Baechle [this message]
2004-01-04 12:05 ` Atsushi Nemoto
2004-01-04 21:03 ` Dimitri Torfs
2004-01-22 10:32 ` Atsushi Nemoto
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