Re: [TRIVIAL] Warn users about machines with non-working WP bit

Pavel Machek
2002-08-19T20:30:57Z

Hi!

> > From: Manfred Spraul <manfred@colorfullife.com>
> > Date: Tue, 06 Aug 2002 11:17:33 +0200
> >
> > > - printk("No.\n");
> > > + printk("No (that's security hole).\n");
> > > #ifdef CONFIG_X86_WP_WORKS_OK
> >
> > Could you explain the hole?
> > WP works for user space apps, only ring0 (or ring 0-2?) code
> > ignores the WP bit on i386.
> >
> >So copy_to_user() could write to user areas that are write-proteced.
> >
> >verify_area() checks aren't enough, consider a threaded application
> >calling mprotect() while the copy is in progress.

> Then we should either fix copy_to_user(), or mark 80386 unsupported, or
> disable multi-threading on 80386. It's a random memory corruption, far
> worse than a security hole.

Fortunately app has to be seriously missbehaving for this to happen. Fixing
copy_to_user would be nicest; I do not think dropping 386 because of *this*
is good idea... [But it might force 386 users to fix copy_to_user ;-)]

Pavel
--
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