linux-kernel - Re: [Patch 0/2] powerpc: avoid userspace poking to legacy ioports

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Date:	Mon, 18 Feb 2008 21:15:19 +0100
From:	Jean Delvare <khali@...ux-fr.org>
To:	benh@...nel.crashing.org
Cc:	Christian Krafft <krafft@...ibm.com>, linux-kernel@...r.kernel.org,
	parabelboi@...serverein.de, linuxppc-dev@...abs.org
Subject: Re: [Patch 0/2] powerpc: avoid userspace poking to legacy ioports

Hi Ben,

On Thu, 14 Feb 2008 07:42:54 +1100, Benjamin Herrenschmidt wrote:
> 
> On Wed, 2008-02-13 at 18:35 +0100, Christian Krafft wrote:
> > sensors_detect crashes kernel on PowerPC, as it pokes directly to memory.

For the records, sensors-detect accesses I/O ports, not memory.

> > This patch adds a check_legacy_ioports to read_port and write_port.
> > It will now return ENXIO, instead of oopsing.
> > 
> > Signed-off-by: Christian Krafft <krafft@...ibm.com>
> 
> The problem is that this prevents using /proc/ioports to access PCI
> IO space, which might be useful.

Maybe Christian's patch can be improved to not do the check on these?
As long as /dev/port exists, it seems reasonable that the kernel should
behave, no matter what I/O ports are accessed from user-space.

> I hate that sensors_detect.. or for that matter any other userland code
> that pokes random ports like that. It should die.

What do you propose as a replacement?

And how is userland code poking at random ports different from kernel
code poking at random ports? We could move sensors-detect inside the
kernel (and I have some plan to do that) but I fail to see how this
would solve this particular problem.

> > Index: linux.git/drivers/char/mem.c
> > ===================================================================
> > --- linux.git.orig/drivers/char/mem.c
> > +++ linux.git/drivers/char/mem.c
> > @@ -566,8 +566,13 @@ static ssize_t read_port(struct file * f
> >  	char __user *tmp = buf;
> >  
> >  	if (!access_ok(VERIFY_WRITE, buf, count))
> > -		return -EFAULT; 
> > +		return -EFAULT;
> > +
> >  	while (count-- > 0 && i < 65536) {
> > +#ifdef CONFIG_PPC_MERGE
> > +		if (check_legacy_ioport(i))
> > +			return -ENXIO;
> > +#endif
> >  		if (__put_user(inb(i),tmp) < 0) 
> >  			return -EFAULT;  
> >  		i++;
> > @@ -585,6 +590,7 @@ static ssize_t write_port(struct file * 
> >  
> >  	if (!access_ok(VERIFY_READ,buf,count))
> >  		return -EFAULT;
> > +
> >  	while (count-- > 0 && i < 65536) {
> >  		char c;
> >  		if (__get_user(c, tmp)) {
> > @@ -592,6 +598,10 @@ static ssize_t write_port(struct file * 
> >  				break;
> >  			return -EFAULT; 
> >  		}
> > +#ifdef CONFIG_PPC_MERGE
> > +		if (check_legacy_ioport(i))
> > +			return -ENXIO;
> > +#endif
> >  		outb(c,i);
> >  		i++;
> >  		tmp++;


-- 
Jean Delvare
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