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Date:   Wed, 9 Feb 2022 09:37:52 +0300
From:   Cyrill Gorcunov <gorcunov@gmail.com>
To:     Dmitry Safonov <0x7f454c46@gmail.com>
Cc:     Mike Rapoport <rppt@kernel.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Adrian Reber <adrian@lisas.de>,
        the arch/x86 maintainers <x86@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Oleg Nesterov <oleg@redhat.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrei Vagin <avagin@gmail.com>,
        Andy Lutomirski <luto@kernel.org>
Subject: Re: [PATCH 00/35] Shadow stacks for userspace
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On Tue, Feb 08, 2022 at 09:54:14PM +0000, Dmitry Safonov wrote:
> [un-Cc'ed a lot of people, as the question is highly off-topic, so I
> don't feel like the answer is of big interest to them, keeping x86
> maintainer in]
> 
> On 2/8/22 17:02, Cyrill Gorcunov wrote:
> >>> Probably a kind of latch in the task_struct which would trigger off once
> >>> returt to a different address happened, thus we would be able to jump inside
> >>> paratite code. Of course such trigger should be available under proper
> >>> capability only.
> >>
> >> I'm not fully in touch with how parasite, etc works.  Are we talking about save or restore?
> > 
> > We use parasite code in question during checkpoint phase as far as I remember.
> > push addr/lret trick is used to run "injected" code (code injection itself is
> > done via ptrace) in compat mode at least. Dima, Andrei, I didn't look into this code
> > for years already, do we still need to support compat mode at all?
> 
> Cyrill, I haven't been working on/with Virtuozzo people last 5 years, so
> I don't know. As you're more connected to Vz, your question seems to
> imply that ia32 C/R is no longer needed by Vz customers. If it's not
> needed anymore - I'm all for stopping testing of it in CRIU.

Nope. I didn't see any sign that Vz is intended to drop ia32 suport. But
Vz's criu instance is following vanilla's one, that is why I asked you
and Andrew about ia32 support. This ia32 code snippet with stack
manipulation simply popped out in my mind immediately when Andy asked
how we deal with stack.

Also we adjust stack in restorer code but I need some time to recall
all thses details since as I said I didn't work with criu code for
years already.

	Cyrill