linux-kernel - Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core)

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Message-ID: <CA+55aFyu=G09-Qg=M-7CmAudS1Mj+OZMPNerd9VfUwvNk8VL+Q@mail.gmail.com>
Date:	Fri, 24 Jun 2016 10:40:46 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Brian Gerst <brgerst@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Andy Lutomirski <luto@...nel.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	Borislav Petkov <bp@...en8.de>,
	Nadav Amit <nadav.amit@...il.com>,
	Kees Cook <keescook@...omium.org>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Jann Horn <jann@...jh.net>,
	Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core)

On Fri, Jun 24, 2016 at 10:21 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> But as mentioned, I must have missed something. There were a number of
> places where the code used the task_stack_page() and
> task_thread_info() interchangably, which used to work and is no longer
> true. There might simply be cases I missed.

.. and immediately as I wrote that, I went "Duh".

One place I missed was free_thread_info(), which should now free the
stack, not the ti pointer. But it does

        struct page *page = virt_to_page(ti);

and frees that, which is bogus. It turns out that we do do

        free_thread_info(tsk->stack);

which is bogus too, and undoes it, but I think I have a few new places
to look at..

                Linus