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

From: Manfred Spraul (
Date: Tue Aug 06 2002 - 09:36:35 EST

Kasper Dupont wrote:

>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(); \

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?


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