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SubjectRe: Warn users about machines with non-working WP bit
Pavel Machek wrote:
>
> Hi!
>
> This might be good idea, as those machines are not safe for multiuser
> systems.
>
> --- clean.2.5/arch/i386/mm/init.c Sun Mar 10 20:06:31 2002
> +++ linux/arch/i386/mm/init.c Mon Mar 11 21:49:14 2002
> @@ -383,7 +383,7 @@
> local_flush_tlb();
>
> if (!boot_cpu_data.wp_works_ok) {
> - printk("No.\n");
> + printk("No (that's security hole).\n");
> #ifdef CONFIG_X86_WP_WORKS_OK
> panic("This kernel doesn't support CPU's with broken WP. Recompile it for a 386!");
> #endif
>
> Pavel

The "bug" is really the lack of a feature present on 486+ cpus. A 386
will allow the kernel to write to a write-protected user page (but not a
write-protected kernel page). In user mode, write protect works as it
should. The kernel works around this by doing extra checks when writing
to user pages (check the *_user() functions). It is not a security
hole, because if the kernel wasn't compiled with the workaround, it
refuses to boot on those cpus.

--

Brian Gerst
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