linux-kernel - Re: [PATCH] seccomp: passthrough uretprobe systemcall without filtering

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Message-ID: <Z4_Riahgmj-bMR8s@krava>
Date: Tue, 21 Jan 2025 17:55:37 +0100
From: Jiri Olsa <olsajiri@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Jiri Olsa <olsajiri@...il.com>, Eyal Birger <eyal.birger@...il.com>,
	Kees Cook <kees@...nel.org>, luto@...capital.net, wad@...omium.org,
	oleg@...hat.com, ldv@...ace.io, mhiramat@...nel.org,
	andrii@...nel.org, alexei.starovoitov@...il.com, cyphar@...har.com,
	songliubraving@...com, yhs@...com, john.fastabend@...il.com,
	peterz@...radead.org, tglx@...utronix.de, bp@...en8.de,
	daniel@...earbox.net, ast@...nel.org, andrii.nakryiko@...il.com,
	rafi@....io, shmulik.ladkani@...il.com, bpf@...r.kernel.org,
	linux-api@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] seccomp: passthrough uretprobe systemcall without
 filtering

On Tue, Jan 21, 2025 at 11:16:31AM -0500, Steven Rostedt wrote:
> 
> [ Watching this with popcorn from the sidelines, but I'll chime in anyway ]
> 
> On Tue, 21 Jan 2025 15:38:48 +0100
> Jiri Olsa <olsajiri@...il.com> wrote:
> 
> > I'm still trying to come up with some other solution but wanted
> > to exhaust all the options I could think of
> 
> I think this may have been mentioned, but is there a way that the kernel
> could know that this system call is being monitored by seccomp, and if so,
> just stick with the interrupt version? If not, enable the system call?

yes [1], the problem with that solution is that we install uretprobe
trampoline at function's uprobe entry probe, so we won't catch case
where seccomp is enabled in this probed function, like:

  foo
    uprobe -> install uretprobe trampoline
    ...
    seccomp(SECCOMP_MODE_STRICT..
    ...
    ret -> execute uretprobe trampoline with sys_uretprobe


I thought we could perhaps switch existing uretprobe trampoline to
int3 when we are in sys_seccomp, but another user thread might be
already executing the existing uretprobe trampoline, so I don't
think we can do that 

jirka


[1] https://lore.kernel.org/bpf/20250114123257.GD19816@redhat.com/