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

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Message-ID: <20250117140924.GA21203@redhat.com>
Date: Fri, 17 Jan 2025 15:09:25 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Eyal Birger <eyal.birger@...il.com>, kees@...nel.org,
	luto@...capital.net, wad@...omium.org, andrii@...nel.org,
	jolsa@...nel.org, alexei.starovoitov@...il.com, olsajiri@...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, rostedt@...dmis.org, 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 01/17, Masami Hiramatsu wrote:
>
> On Fri, 17 Jan 2025 02:39:28 +0100
> Oleg Nesterov <oleg@...hat.com> wrote:
>
> > A note for the seccomp maintainers...
> >
> > I don't know what do you think, but I agree in advance that the very fact this
> > patch adds "#ifdef CONFIG_X86_64" into __secure_computing() doesn't look nice.
> >
>
> Indeed. in_ia32_syscall() depends arch/x86 too.
> We can add an inline function like;
>
> ``` uprobes.h
> static inline bool is_uprobe_syscall(int syscall)
> {

We can, and this is what I tried to suggest from the very beginning.
But I agree with Eyal who decided to send the most trivial fix for
-stable, we can add the helper later.

I don't think it should live in uprobes.h and I'd prefer something
like arch_seccomp_ignored(int) but I won't insist.

> 	// arch_is_uprobe_syscall check can be replaced by Kconfig,
> 	// something like CONFIG_ARCH_URETPROBE_SYSCALL.

Or sysctl or both. This is another issue.

> ``` arch/x86/include/asm/uprobes.h
> #define arch_is_uprobe_syscall(syscall) \
> 	(IS_ENABLED(CONFIG_X86_64) && syscall == __NR_uretprobe && !in_ia32_syscall())
> ```

This won't compile if IS_ENABLED(CONFIG_X86_64) == false, __NR_uretprobe
will be undefined.

> > The problem is that we need a simple patch for -stable which fixes the real
> > problem. We can cleanup this logic later, I think.
>
> Hmm, at least we should make it is_uprobe_syscall() in uprobes.h so that
> do not pollute the seccomp subsystem with #ifdef.

See above. But I won't insist.

Oleg.