Messages in this thread | | | Date | Wed, 03 Apr 2002 17:24:51 -0500 | From | Brian Gerst <> | Subject | Re: Warn users about machines with non-working WP bit |
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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.
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