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From: Jiri Olsa <olsajiri@gmail.com>
Date: Tue, 9 Apr 2024 14:06:19 +0200
To: Oleg Nesterov <oleg@redhat.com>
Cc: Jiri Olsa <olsajiri@gmail.com>, Masami Hiramatsu <mhiramat@kernel.org>,
	Andrii Nakryiko <andrii.nakryiko@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>, linux-kernel@vger.kernel.org,
	linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org,
	Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	"Borislav Petkov (AMD)" <bp@alien8.de>, x86@kernel.org,
	linux-api@vger.kernel.org
Subject: Re: [PATCHv2 1/3] uprobe: Add uretprobe syscall to speed up return
 probe
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On Mon, Apr 08, 2024 at 06:22:59PM +0200, Oleg Nesterov wrote:
> On 04/08, Jiri Olsa wrote:
> >
> > On Fri, Apr 05, 2024 at 01:02:30PM +0200, Oleg Nesterov wrote:
> > >
> > > And what should sys_uretprobe() do if it is not called from the trampoline?
> > > I'd prefer force_sig(SIGILL) to punish the abuser ;) OK, OK, EINVAL.
> >
> > so the similar behaviour with int3 ends up with immediate SIGTRAP
> > and not invoking pending uretprobe consumers, like:
> >
> >   - setup uretprobe for foo
> >   - foo() {
> >       executes int 3 -> sends SIGTRAP
> >     }
> >
> > because the int3 handler checks if it got executed from the uretprobe's
> > trampoline.
> 
> ... or the task has uprobe at this address
> 
> > if not it treats that int3 as regular trap
> 
> Yes this mimics the "default" behaviour without uprobes/uretprobes
> 
> > so I think we should mimic int3 behaviour and:
> >
> >   - setup uretprobe for foo
> >   - foo() {
> >      uretprobe_syscall -> check if we got executed from uretprobe's
> >      trampoline and send SIGILL if that's not the case
> 
> Agreed,
> 
> > I think it's better to have the offending process killed right away,
> > rather than having more undefined behaviour, waiting for final 'ret'
> > instruction that jumps to uretprobe trampoline and causes SIGILL
> 
> Agreed. In fact I think it should be also killed if copy_to/from_user()
> fails by the same reason.

+1 makes sense

jirka

> 
> Oleg.
>