linux-kernel - Re: [PATCH v6 1/2] ptrace,syscall_user_dispatch: Implement Syscall User Dispatch Suspension

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Message-ID: <Y9IE5tBjY1GlFCFH@memverge.com>
Date:   Wed, 25 Jan 2023 23:43:18 -0500
From:   Gregory Price <gregory.price@...verge.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Gregory Price <gourry.memverge@...il.com>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        avagin@...il.com, peterz@...radead.org, luto@...nel.org,
        krisman@...labora.com, tglx@...utronix.de, corbet@....net,
        shuah@...nel.org
Subject: Re: [PATCH v6 1/2] ptrace,syscall_user_dispatch: Implement Syscall
 User Dispatch Suspension

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.
> 

After further investigation, I believe we can drop 1/2, but for a
different reason:  It's actually insane behavior during the quiesce
phase.  Quiesce allows the program to run until a particular state,
which means we can't turn it off lest we interfere with intended
behavior - (cough cough prior review said this cough cough i'm dumb).

I'll drop patch 1/2 and resubmit (there's an unused variable warning i
need to clean up).

Thanks again for the reviews all
~Gregory