From: Gregory Price <gregory.price@memverge.com>
To: Andrei Vagin <avagin@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>,
Gregory Price <gourry.memverge@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Andy Lutomirski <luto@kernel.org>,
Gabriel Krisman Bertazi <krisman@collabora.com>,
Thomas Gleixner <tglx@linutronix.de>,
Jonathan Corbet <corbet@lwn.net>, Shuah Khan <shuah@kernel.org>,
Mike Rapoport <rppt@kernel.org>
Subject: Re: [PATCH v6 1/2] ptrace,syscall_user_dispatch: Implement Syscall User Dispatch Suspension
Date: Thu, 26 Jan 2023 12:52:25 -0500 [thread overview]
Message-ID: <Y9K92SQnrXhd0qjC@memverge.com> (raw)
In-Reply-To: <CANaxB-woave9F479O75P9PC+nFO3DVmbeFA1rXf2c=bhRmWoiQ@mail.gmail.com>
On Thu, Jan 26, 2023 at 09:45:39AM -0800, Andrei Vagin wrote:
> On Thu, Jan 26, 2023 at 7:07 AM Oleg Nesterov <oleg@redhat.com> wrote:
> >
> > On 01/25, Andrei Vagin wrote:
> > >
> > > On Wed, Jan 25, 2023 at 4:30 PM Oleg Nesterov <oleg@redhat.com> 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,
> > >
> > > PTRACE_O_SUSPEND_SYSCALL_USER_DISPATCH is automatically cleared when
> > > a tracer detaches. It is critical when tracers detach due to unexpected
> > > reasons
> >
> > IIUC, PTRACE_O_SUSPEND_SYSCALL_USER_DISPATCH is needed to run the injected
> > code, and this also needs to change the state of the traced process. If
> > the tracer (CRIU) dies while the tracee runs this code, I guess the tracee
> > will have other problems?
>
> Our injected code can reheal itself if something goes wrong. The hack
> here is that we inject
> the code with a signal frame and it calls rt_segreturn to resume the process.
>
> We want to have this functionality for most cases. I don't expect that
> the syscall user dispatch
> is used by many applications, so I don't strongly insist on
> PTRACE_O_SUSPEND_SYSCALL_USER_DISPATCH. In addition, if we know a user dispatch
> memory region, it can be enough to inject our code out of this region
> without disabling SUD.
>
> Thanks,
> Andrei
The region is exclusive, so syscalls *outside* [offset, offset+len]
produce a dispatch. That means you would have to inject into that region.
That's what's problematic for injection. Even rt_sigreturn itself
may/will be intercepted.
next prev parent reply other threads:[~2023-01-26 17:52 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
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 [this message]
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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