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Date:   Tue, 8 Feb 2022 11:16:51 +0200
From:   Mike Rapoport <rppt@kernel.org>
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     Adrian Reber <adrian@lisas.de>,
        Rick Edgecombe <rick.p.edgecombe@intel.com>, x86@kernel.org,
        "H . Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        linux-doc@vger.kernel.org, linux-mm@kvack.org,
        linux-arch@vger.kernel.org, linux-api@vger.kernel.org,
        Arnd Bergmann <arnd@arndb.de>,
        Andy Lutomirski <luto@kernel.org>,
        Balbir Singh <bsingharora@gmail.com>,
        Borislav Petkov <bp@alien8.de>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Eugene Syromiatnikov <esyr@redhat.com>,
        Florian Weimer <fweimer@redhat.com>,
        "H . J . Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Kees Cook <keescook@chromium.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Nadav Amit <nadav.amit@gmail.com>,
        Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
        Peter Zijlstra <peterz@infradead.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        "Ravi V . Shankar" <ravi.v.shankar@intel.com>,
        Dave Martin <Dave.Martin@arm.com>,
        Weijiang Yang <weijiang.yang@intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        joao.moreira@intel.com, John Allen <john.allen@amd.com>,
        kcc@google.com, eranian@google.com,
        Andrei Vagin <avagin@gmail.com>,
        Dmitry Safonov <0x7f454c46@gmail.com>
Subject: Re: [PATCH 00/35] Shadow stacks for userspace
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On Mon, Feb 07, 2022 at 08:30:50AM -0800, Dave Hansen wrote:
> On 2/6/22 23:20, Adrian Reber wrote:
> >>> 	CRIU Support
> >>> 	------------
> >>> 	In the past there was some speculation on the mailing list about 
> >>> 	whether CRIU would need to be taught about CET. It turns out, it does. 
> >>> 	The first issue hit is that CRIU calls sigreturn directly from its 
> >>> 	“parasite code” that it injects into the dumper process. This violates
> >>> 	this shadow stack implementation’s protection that intends to prevent
> >>> 	attackers from doing this.
> ...
> >>From the CRIU side I can say that I would definitely like to see this
> > resolved. CRIU just went through a similar exercise with rseq() being
> > enabled in glibc and CI broke all around for us and other projects
> > relying on CRIU. Although rseq() was around for a long time we were not
> > aware of it but luckily 5.13 introduced a way to handle it for CRIU with
> > ptrace. An environment variable existed but did not really help when
> > CRIU is called somewhere in the middle of the container software stack.
> > 
> >>From my point of view a solution not involving an environment variable
> > would definitely be preferred.
> 
> Have there been things like this for CRIU in the past?  Something where
> CRIU needs control but that's also security-sensitive?

Generally CRIU requires (almost) root privileges to work, but I don't think
it handles something as security sensitive and restrictive as shadow stacks. 
 
> Any thoughts on how you would _like_ to see this resolved?

Ideally, CRIU will need a knob that will tell the kernel/CET machinery
where the next RET will jump, along the lines of
restore_signal_shadow_stack() AFAIU.

But such a knob will immediately reduce the security value of the entire
thing, and I don't have good ideas how to deal with it :(

-- 
Sincerely yours,
Mike.