From: Gregory Price <gregory.price@memverge.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Gregory Price <gourry.memverge@gmail.com>,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
avagin@gmail.com, peterz@infradead.org, luto@kernel.org,
krisman@collabora.com, tglx@linutronix.de, corbet@lwn.net,
shuah@kernel.org
Subject: Re: [PATCH v6 1/2] ptrace,syscall_user_dispatch: Implement Syscall User Dispatch Suspension
Date: Wed, 25 Jan 2023 20:30:32 -0500 [thread overview]
Message-ID: <Y9HXuF95LeqSWTB9@memverge.com> (raw)
In-Reply-To: <20230126003008.GA31684@redhat.com>
On Thu, Jan 26, 2023 at 01:30:08AM +0100, Oleg Nesterov wrote:
> On 01/24, Gregory Price wrote:
> >
> > Adds PTRACE_O_SUSPEND_SYSCALL_USER_DISPATCH to ptrace options, and
> > modify Syscall User Dispatch to suspend interception when enabled.
> >
> > This is modeled after the SUSPEND_SECCOMP feature, which suspends
> > SECCOMP interposition. Without doing this, software like CRIU will
> > inject system calls into a process and be intercepted by Syscall
> > User Dispatch, either causing a crash (due to blocked signals) or
> > the delivery of those signals to a ptracer (not the intended behavior).
>
> Cough... Gregory, I am sorry ;)
>
> but can't we drop this patch to ?
>
> CRIU needs to do PTRACE_SET_SYSCALL_USER_DISPATCH_CONFIG and check
> config->mode anyway as we discussed.
>
> Then it can simply set *config->selector = SYSCALL_DISPATCH_FILTER_ALLOW
> with the same effect, no?
>
> Oleg.
>
The selector is optional, but the core idea seems reasonable.
Though I think this complicates the quiesce vs checkpoint phases a bit.
My best understanding of CRIU is there are (at least) two checkpoint
phases: quiesce and checkpoint. The intent of patch 1/2 is to aid the
quiesce phase, not the checkpoint phase.
In both phases the `compel` code is used to inject system calls, so
turning SUD off is required. That can obviously be achieved via saving
with get_config, and just clearing it entirely with set_config.
I'm NOT sure whether the `compel` code can save settings that the
`cr-check` code then saves to disc, or if `compel` is standalone. I will
go check this and report back.
The only other concern is one of how it's restored, and in what order
compared to SECCOMP - for the absolute insane case of someone running a
SUD task inside a locked down cgroup? Technically possible (TM)!
We may find that the suspend flag is "just easier" but not required.
I do think more-simple-is-more-better, though, so I will investigate.
~Gregory
next prev parent reply other threads:[~2023-01-26 1:31 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-25 2:51 [PATCH v6 0/2] Gregory Price
2023-01-25 2:51 ` [PATCH v6 1/2] ptrace,syscall_user_dispatch: Implement Syscall User Dispatch Suspension Gregory Price
2023-01-26 0:30 ` Oleg Nesterov
2023-01-26 1:30 ` Gregory Price [this message]
2023-01-26 4:43 ` Gregory Price
[not found] ` <CANaxB-xn0wW5xA_CT7bA5=jig+td__EDKPBWSpZdfgMgVOezCg@mail.gmail.com>
2023-01-26 5:26 ` Gregory Price
2023-01-26 15:10 ` Oleg Nesterov
2023-01-26 18:09 ` Andrei Vagin
2023-01-26 15:07 ` Oleg Nesterov
2023-01-26 17:45 ` Andrei Vagin
2023-01-26 17:52 ` Gregory Price
2023-01-26 18:30 ` Andrei Vagin
2023-01-26 18:30 ` Oleg Nesterov
2023-01-26 18:46 ` Gregory Price
2023-01-26 18:53 ` Andrei Vagin
2023-01-26 19:01 ` Gregory Price
2023-01-25 2:51 ` [PATCH v6 2/2] ptrace,syscall_user_dispatch: add a getter/setter for sud configuration Gregory Price
2023-01-25 7:14 ` kernel test robot
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