linux-kernel - Re: [RFC PATCH 00/16] PTI support for x86-32

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Date:   Tue, 16 Jan 2018 20:55:43 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Brian Gerst <brgerst@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>,
        "Liguori, Anthony" <aliguori@...zon.com>,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>,
        Hugh Dickins <hughd@...gle.com>,
        Kees Cook <keescook@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Waiman Long <llong@...hat.com>, Joerg Roedel <jroedel@...e.de>
Subject: Re: [RFC PATCH 00/16] PTI support for x86-32

Hi Linus,

On Tue, Jan 16, 2018 at 10:59:01AM -0800, Linus Torvalds wrote:
> Yes, I'm very happy to see that this is actually not nearly as bad as
> I feared it might be,

Yeah, I was looking at the original PTI patches and my impression was
that a lot of the complicated stuff (like setting up the cpu_entry_area)
was already in there for 32 bit too. So it was mostly about the entry
code and some changes to the 32bit page-table code.

> Some of those #ifdef's in the PTI code you added might want more
> commentary about what the exact differences are. And maybe they could
> be done more cleanly with some abstraction. But nothing looked
> _horrible_.

I'll add more comments and better abstraction, Dave has already
suggested some improvements here. Reading some of my comments again,
they need a rework anyway.

> .. and please run all the segment and syscall selfchecks that Andy has written.

Didn't know about them yet, thanks. I will run them too in my testing

> Xen PV and PTI don't work together even on x86-64 afaik, the Xen
> people apparently felt it wasn't worth it.  See the
> 
>         if (hypervisor_is_type(X86_HYPER_XEN_PV)) {
>                 pti_print_if_insecure("disabled on XEN PV.");
>                 return;
>         }
> 
> in pti_check_boottime_disable().

But I might have broken something for them anyway, honestly I didn't pay
much attention to the XEN_PV case as I was trying to get it running
here. My hope is that someone who knows Xen better than I do will help
out :)


Regards,

	Joerg