linux-kernel - Re: [PATCH v2] panic: Taint kernel if fault injection has been used

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Message-ID: <20221204223001.6wea7cgkofjsiy2z@macbook-pro-6.dhcp.thefacebook.com>
Date:   Sun, 4 Dec 2022 14:30:01 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, bpf@...r.kernel.org,
        Borislav Petkov <bp@...en8.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        KP Singh <kpsingh@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Florent Revest <revest@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        Chris Mason <clm@...a.com>
Subject: Re: [PATCH v2] panic: Taint kernel if fault injection has been used

On Mon, Dec 05, 2022 at 07:22:44AM +0900, Masami Hiramatsu (Google) wrote:
> From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> 
> Since the function error injection framework in the fault injection
> subsystem can change the function code flow forcibly, it may cause
> unexpected behavior (and that is the purpose of this feature) even
> if it is applied to the ALLOW_ERROR_INJECTION functions.
> So this feature must be used only for debugging or testing purpose.

The whole idea of tainting for kernel debugging is questionable.
There are many other *inject* kconfigs and other debug flags
for link lists, RCU, sleeping, etc.
None of them taint the kernel.

> To identify this in the kernel oops message, add a new taint flag

Have you ever seen a single oops message because of this particular
error injection?

> for the fault injection. This taint flag will be set by either
> function error injection is used or the BPF use the kprobe_override
> on error injectable functions (identified by ALLOW_ERROR_INJECTION).

...

>  	/* set the new array to event->tp_event and set event->prog */
> +	if (prog->kprobe_override)
> +		add_taint(TAINT_FAULT_INJECTED, LOCKDEP_NOW_UNRELIABLE);

Nack for bpf bits.