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

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Message-ID: <20250114112106.GC19816@redhat.com>
Date: Tue, 14 Jan 2025 12:21:07 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Jiri Olsa <olsajiri@...il.com>, Aleksa Sarai <cyphar@...har.com>,
	Eyal Birger <eyal.birger@...il.com>,
	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>, peterz@...radead.org,
	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, Masami Hiramatsu wrote:
>
> On Tue, 14 Jan 2025 10:22:20 +0100
> Jiri Olsa <olsajiri@...il.com> wrote:
>
> > @@ -418,6 +439,9 @@ SYSCALL_DEFINE0(uretprobe)
> >  	regs->r11 = regs->flags;
> >  	regs->cx  = regs->ip;
> >
> > +	/* zero rbx to signal trampoline that uretprobe syscall was executed */
> > +	regs->bx  = 0;
>
> Can we just return -ENOSYS as like as other syscall instead of
> using rbx as a side channel?
> We can carefully check the return address is not -ERRNO when set up
> and reserve the -ENOSYS for this use case.

Not sure I understand...

But please not that the uretprobed function can return any value
including -ENOSYS, and this is what sys_uretprobe() has to return.

Oleg.