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

Pavel Machek
2002-08-19T20:30:58Z

Hi!

> >I just get another idea, that might be easier to get right. If
> >the only problem is one process changing the mm while another
> >process is doing a copy_to_user, we should be able to fix it by
> >placing a readlock on the mm while the copy_to_user is in progress.
> >
> >
> Yes, that would work. copy_to_user is never called with the mmap
> semaphore locked, i.e.
>
> #define copy_to_user(...) > down(&current->mm->mmap_sem); > check_wp_bit(); > real_copy_to_user(); > up(&current->mm->mmap_sem)
>
> verify_area would just check that the pointer is below TASK_SIZE, and
> the wp bit is checked within copy_to_user().
>
> But how many 80386 Linux systems that run the 2.4 kernel exist?

Many embedded boxes, I beieve, have modern 386 CPUs.
Pavel
--
Philips Velo 1: 1"x4"x8", 300gram, 60, 12MB, 40bogomips, linux, mutt,
details at http://atrey.karlin.mff.cuni.cz/~pavel/velo/index.html.