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From: Jamie Lokier <jamie@shareable.org>
To: Paul Mackerras <paulus@samba.org>
Cc: Gabriel Paubert <paubert@iram.es>,
	linuxppc-dev@lists.linuxppc.org, linux-kernel@vger.kernel.org
Subject: Re: A question about PROT_NONE on PPC and PPC64
Date: Mon, 5 Jul 2004 20:11:58 +0100	[thread overview]
Message-ID: <20040705191158.GA4457@mail.shareable.org> (raw)
In-Reply-To: <20040705155908.GA23163@iram.es>

Hi Paul,

Gabriel Paubert tells me that PROT_NONE _might_ have the bug described
below on the PPC 4xx and 8xx architectures, because their MMUs don't
implement "Ks = Kp = 1" segments.

Can you or someone else confirm whether the potential bug occurs on
PPC 4xx/8xx?

Thanks,
-- Jamie

Paul Mackerras wrote:
> > It appears the only difference betwen PROT_READ and PROT_NONE is
> > whether _PAGE_USER is set.
> > 
> > Thus PROT_NONE pages aren't readable from userspace, but it appears
> > they _are_ readable from kernel space.  Is this correct?
> 
> No.  Kernel accesses to pages in the user portion of the address space
> (0 .. TASK_SIZE-1) are done using the user permissions.  On classic
> PPC this is implemented (in part) by setting Ks = Kp = 1 in the
> segment descriptors for the user segments, which tells the hardware to
> check the access as if it was a user access even in supervisor mode.

      parent reply	other threads:[~2004-07-05 19:12 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2004-06-30  3:18 Jamie Lokier
2004-06-30  4:47 ` Paul Mackerras
     [not found] ` <20040705072731.GB19707@iram.es>
     [not found]   ` <20040705142046.GB3411@mail.shareable.org>
     [not found]     ` <20040705155908.GA23163@iram.es>
2004-07-05 19:11       ` Jamie Lokier [this message]

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