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Date: Mon, 8 Apr 2024 18:22:59 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Jiri Olsa <olsajiri@gmail.com>
Cc: 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
Message-ID: <20240408162258.GC25058@redhat.com>
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User-Agent: Mutt/1.5.24 (2015-08-30)

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.

Oleg.