linux-kernel - Re: Crash when attaching uretprobes to processes running in Docker

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Message-ID: <20250114123257.GD19816@redhat.com>
Date: Tue, 14 Jan 2025 13:32:58 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Jiri Olsa <olsajiri@...il.com>, Aleksa Sarai <cyphar@...har.com>,
	Eyal Birger <eyal.birger@...il.com>, mhiramat@...nel.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-trace-kernel@...r.kernel.org,
	BPF-dev-list <bpf@...r.kernel.org>,
	Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
	John Fastabend <john.fastabend@...il.com>, tglx@...utronix.de,
	bp@...en8.de, x86@...nel.org, linux-api@...r.kernel.org,
	Andrii Nakryiko <andrii@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Alexei Starovoitov <ast@...nel.org>,
	Andrii Nakryiko <andrii.nakryiko@...il.com>,
	"rostedt@...dmis.org" <rostedt@...dmis.org>, rafi@....io,
	Shmulik Ladkani <shmulik.ladkani@...il.com>
Subject: Re: Crash when attaching uretprobes to processes running in Docker

On 01/14, Peter Zijlstra wrote:
>
> On Tue, Jan 14, 2025 at 12:01:50PM +0100, Oleg Nesterov wrote:
> > On 01/14, Peter Zijlstra wrote:
> > >
> > > On Tue, Jan 14, 2025 at 10:22:20AM +0100, Jiri Olsa wrote:
> > > >
> > > > hack below seems to fix the issue, it's using rbx to signal that uretprobe
> > > > syscall got executed, if not, trampoline does int3 and executes uretprobe
> > > > handler in the old way
> > > >
> > > > unfortunately now the uretprobe trampoline size crosses the xol slot limit so
> > > > will need to come up with some generic/arch code solution for that, code below
> > > > is neglecting that for now
> > >
> > > Can't you detect the filter earlier and simply not install the
> > > trampoline?
> >
> > Did you mean detect the filter in prepare_uretprobe() ?
>
> Yep. Aren't syscall filters static for the duration of the task?
>
> > The probed function can install the filter before return...
>
> If you're running a task with dynamic syscall filtering, you get to keep
> the pieces no?

Sorry, I don't understand... Perhaps because I am enjoying my state after
dentist appointment ;)

OK, suppose we have

	void start_SECCOMP_MODE_STRICT(void)
	{
		// in particular nacks __NR_uretprobe
		seccomp(SECCOMP_MODE_STRICT, ...);
	}

and we want to add uretprobe to this function.

In this case prepare_uretprobe() can't know that sys_uretprobe() won't
work when this function returns?

Oleg.