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

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Message-ID: <Z4Zy6W6z3ICp6SdJ@krava>
Date: Tue, 14 Jan 2025 15:21:29 +0100
From: Jiri Olsa <olsajiri@...il.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, 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 Tue, Jan 14, 2025 at 12:21:07PM +0100, Oleg Nesterov wrote:
> 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.

right, uretprobe syscall returns value of the uretprobed function,
so we can't use any reserved value

jirka