Re: [PATCH] Futexes IV (Fast Lightweight Userspace Semaphores)

Pavel Machek
2002-03-12T14:27:42Z

Hi!

> >So if anything its just not worth the effort of breaking the 386 setup
> >either 8). 386 SMP is a different issue but I don't see any lunatics doing
> >a 386 based sequent port thankfully.
>
> Since the only person that comes to mind that would be crazy enough to
> even _try_ to use Linux on 386-SMP is you, Alan, I'm really relieved to
> hear you say that ;)
>
> And no, it's not worth discontinuing i386 support. It just isn't
> painful enough to maintain.
>
> Note that the i386 has _long_ been a "stepchild", though: because of the
> lack of WP, the kernel simply doesn't do threaded MM correctly on a 386.
> Never has, and never will.
>
> However, the known "incorrect" case is so obscure that it's not even an
> issue - although I suspect that it means that you should not let
> untrusted users run on a i386 server machine that contains any sensitive
> data. I could cerrtainly come up with exploits that would work at least
> in theory (whether they are workable in practice I don't know).

That should mean at least warning during bootup. Checking for WP
bit... message does not suggest that WP not present means security
hole.

--- 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
--
(about SSSCA) "I don't say this lightly. However, I really think that the U.S.
no longer is classifiable as a democracy, but rather as a plutocracy." --hpa