linux-kernel - Re: [PATCH] error-injection: Add prompt for function error injection

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Date:   Fri, 2 Dec 2022 18:17:24 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Theodore Ts'o <tytso@....edu>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Chris Mason <clm@...a.com>, Borislav Petkov <bp@...en8.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Masami Hiramatsu <mhiramat@...nel.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>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>
Subject: Re: [PATCH] error-injection: Add prompt for function error
 injection

On Fri, 2 Dec 2022 13:27:11 -0800
Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:

> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1874,8 +1874,12 @@ config NETDEV_NOTIFIER_ERROR_INJECT
>  	  If unsure, say N.
>  
>  config FUNCTION_ERROR_INJECTION

Why not just call this "ERROR_INJECTION" having this be FUNCTION and the
one for functions be FUNC is confusing.

> +        bool
> +
> +config FUNC_ERROR_INJECTION
>  	bool "Fault-injections of functions"
>  	depends on HAVE_FUNCTION_ERROR_INJECTION && KPROBES
> +	select FUNCTION_ERROR_INJECTION
>  	help
>  	  Add fault injections into various functions that are annotated with
>  	  ALLOW_ERROR_INJECTION() in the kernel. BPF may also modify the return
> @@ -1883,6 +1887,17 @@ config FUNCTION_ERROR_INJECTION
>  
>  	  If unsure, say N
>  
> +config SYSCALL_ERROR_INJECTION
> +	bool "Error injections in syscalls"
> +	depends on HAVE_FUNCTION_ERROR_INJECTION && KPROBES
> +	select FUNCTION_ERROR_INJECTION
> +	default y

IIUC, Linus prefers everything to be "default n" unless there's a really
good reason for it. Like only making other options available, but not doing
anything to the kernel. I do have DYNAMIC_FTRACE as "default y" but that's
only because it depends on CONFIG_FUNCTION_TRACER and nobody that enables
that should have DYNAMIC_FTRACE off (except for academia).

> +	help
> +	  Allows error injection framework to return errors from syscalls.
> +	  BPF may modify return values of syscalls as well.

And here's the thing. If BPF returns anything *but* an error, then this is
a misnomer and incorrect. Name it something else like "HIJACK_SYSCALLS".

> +
> +	  If unsure, say Y

And I'm curious, why Y if unsure?

-- Steve

> +
>  config FAULT_INJECTION
>  	bool "Fault-injection framework"
>  	depends on DEBUG_KERNEL
> diff --git a/lib/error-inject.c b/lib/error-inject.c
> index 1afca1b1cdea..9ba868eb8c43 100644
> --- a/lib/error-inject.c
> +++ b/lib/error-inject.c
> @@ -71,6 +71,10 @@ static void populate_error_injection_list(struct error_injection_entry *start,
>  
>  	mutex_lock(&ei_mutex);
>  	for (iter = start; iter < end; iter++) {
> +		if (iter->etype != EI_ETYPE_SYSCALL &&
> +		    !IS_ENABLED(CONFIG_FUNC_ERROR_INJECTION))
> +			continue;
> +
>  		entry = (unsigned long)dereference_symbol_descriptor((void *)iter->addr);
>  
>  		if (!kernel_text_address(entry) ||
> @@ -189,6 +193,8 @@ static const char *error_type_string(int etype)
>  		return "ERRNO_NULL";
>  	case EI_ETYPE_TRUE:
>  		return "TRUE";
> +	case EI_ETYPE_SYSCALL:
> +		return "SYSCALL";
>  	default:
>  		return "(unknown)";
>  	}