linux-kernel - Re: generic uaccess.h

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Date:	Mon, 27 Jul 2009 20:18:33 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	monstr@...str.eu
Cc:	Linux Kernel list <linux-kernel@...r.kernel.org>,
	John Williams <john.williams@...alogix.com>
Subject: Re: generic uaccess.h

On Monday 27 July 2009, Michal Simek wrote:
> I am getting any short write error. It is caused with adding access_ok macro.
> It is weird.

Your implementation of access_ok() is minimal, but should be ok
in theory. Note that even on nommu, it might make sense
to check for kernel addresses here and implement get_fs/set_fs,
e.g.

int access_ok(int type, unsigned long addr, size_t len)
{
	/* check wraparound */
	if (addr + len < addr)
		return 0;

	if (addr < memory_start || addr + len > memory_start)
		return 0;

	/* don't allow access to kernel memory */
	if (get_fs() == USER_DS) {
		if (is_kernel(addr) || is_kernel(addr + len))
			return 0;
	}

	return 1;
}

> I have more important work in front of me - I take a look at it later.

ok. When you get to debug this, I guess the easiest way is to stick
some printk into your access_ok() function.

	Arnd <><
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