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Date:   Thu, 1 Dec 2022 23:41:21 +0900
From:   Masami Hiramatsu (Google) <mhiramat@kernel.org>
To:     Chris Mason <clm@meta.com>
Cc:     Borislav Petkov <bp@alien8.de>,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Kees Cook <keescook@chromium.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        KP Singh <kpsingh@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Florent Revest <revest@chromium.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH] error-injection: Add prompt for function error
 injection
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Hi,

On Tue, 22 Nov 2022 12:42:33 -0500
Chris Mason <clm@meta.com> wrote:
> 
> - fault injection for testing: we have a stage of qualification that
> does error injection against the prod kernel.  It helps to have this
> against the debug kernel too, but that misses some races etc.  I always
> just assumed distros and partners did some fault injection tests against
> the prod kernel builds?
> 
> - fault injection for debugging:  it doesn't happen often but at some
> point we run out of ideas and start making different functions fail in
> prod to figure out why we're not prodding.

For those purpose, isn't it enough to add a taint flag for the fault
injection? This will help us to identify that the kernel is possible
to be under debug mode.

> - overriding return values for security fixes: also not a common thing,
> but it's a tool we've used.  There are usually better long term fixes,
> but it happens.

I don't recommend to use the fault injection for this purpose. For fixing
the security issue online, you should use livepatch.

Thank you,

-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>