From nobody Thu Sep 18 04:33:23 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2A511C001B2 for ; Mon, 12 Dec 2022 02:47:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230495AbiLLCrY (ORCPT ); Sun, 11 Dec 2022 21:47:24 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49370 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231178AbiLLCrE (ORCPT ); Sun, 11 Dec 2022 21:47:04 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0769DDECF; Sun, 11 Dec 2022 18:47:01 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 745FCB80B08; Mon, 12 Dec 2022 02:47:00 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4C3CDC433EF; Mon, 12 Dec 2022 02:46:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1670813219; bh=Nyp9/17nJoeIVRs1IwJjhY9sDOm3rRLOwsEBQ9/ixsc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Y8gc2wxVZ3E0Iz00qGjm+3CygLhe0W8P9+qVDA2/+R1PRyIeCtAwqJi9waNW+Hlw7 lpKgM41Ksk9vhCwguNwBPizVUBS2jg4p/dzgR7qLUbdN4kA7oIVodgu3sfFVvCRzAn JYxbpUGly2jdw5G/PLYUlUuZz7IChj404/GXgeRrRLETh3FDdxbyVJ5lOb1ah1KNC+ NwH5znNKz/+cvKGQYgnSY0+NUsxFmBTZCcc6+iL2bA8U0M3UFVuw6rDjJQjC3j4Ij/ 0bvo5HwS0ZZcH8G/PFTqKnYg+fRYW0I1A3jb3Ovk+7LAkY5dkEx+HBJ25/ElihNqGA ZlWuwoGeLlbCQ== From: "Masami Hiramatsu (Google)" To: LKML Cc: bpf@vger.kernel.org, Borislav Petkov , Alexei Starovoitov , Steven Rostedt , Linus Torvalds , Masami Hiramatsu , Andrew Morton , Peter Zijlstra , Kees Cook , Josh Poimboeuf , KP Singh , Mark Rutland , Florent Revest , Greg Kroah-Hartman , Christoph Hellwig , Chris Mason , Jonathan Corbet , linux-doc@vger.kernel.org Subject: [PATCH 2/2] docs: fault-injection: Add requirements of error injectable functions Date: Mon, 12 Dec 2022 11:46:54 +0900 Message-Id: <167081321427.387937.15475445689482551048.stgit@devnote3> X-Mailer: git-send-email 2.39.0.rc1.256.g54fd8350bd-goog In-Reply-To: <167081319306.387937.10079195394503045678.stgit@devnote3> References: <167081319306.387937.10079195394503045678.stgit@devnote3> User-Agent: StGit/0.19 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Masami Hiramatsu (Google) Add a section about the requirements of the error injectable functions and the type of errors. Since this section must be read before using ALLOW_ERROR_INJECTION() macro, that section is referred from the comment of the macro too. Signed-off-by: Masami Hiramatsu (Google) Link: https://lore.kernel.org/all/20221211115218.2e6e289bb85f8cf53c11aa97@k= ernel.org/T/#u --- Documentation/fault-injection/fault-injection.rst | 65 +++++++++++++++++= ++++ include/asm-generic/error-injection.h | 6 +- 2 files changed, 69 insertions(+), 2 deletions(-) diff --git a/Documentation/fault-injection/fault-injection.rst b/Documentat= ion/fault-injection/fault-injection.rst index 17779a2772e5..da6c5796b1f8 100644 --- a/Documentation/fault-injection/fault-injection.rst +++ b/Documentation/fault-injection/fault-injection.rst @@ -233,6 +233,71 @@ proc entries This feature is intended for systematic testing of faults in a single system call. See an example below. =20 + +Error Injectable Functions +-------------------------- + +This part is for the kenrel developers considering to add a function to +ALLOW_ERROR_INJECTION() macro. + +Requirements for the Error Injectable Functions +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Since the function-level error injection forcibly changes the code path +and returns an error even if the input and conditions are proper, this can +cause unexpected kernel crash if you allow error injection on the function +which is NOT error injectable. Thus, you (and reviewers) must ensure; + +- The function returns an error code if it fails, and the callers must che= ck + it correctly (need to recover from it). + +- The function does not execute any code which can change any state before + the first error return. The state includes global or local, or input + variable. For example, clear output address storage (e.g. `*ret =3D NULL= `), + increments/decrements counter, set a flag, preempt/irq disable or get + a lock (if those are recovered before returning error, that will be OK.) + +The first requirement is important, and it will result in that the release +(free objects) functions are usually harder to inject errors than allocate +functions. If errors of such release functions are not correctly handled +it will cause a memory leak easily (the caller will confuse that the object +has been released or corrupted.) + +The second one is for the caller which expects the function should always +does something. Thus if the function error injection skips whole of the +function, the expectation is betrayed and causes an unexpected error. + +Type of the Error Injectable Functions +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Each error injectable functions will have the error type specified by the +ALLOW_ERROR_INJECTION() macro. You have to choose it carefully if you add +a new error injectable function. If the wrong error type is chosen, the +kernel may crash because it may not be able to handle the error. +There are 4 types of errors defined in include/asm-generic/error-injection= .h + +EI_ETYPE_NULL + This function will return `NULL` if it fails. e.g. return an allocateed + object address. + +EI_ETYPE_ERRNO + This function will return an `-errno` error code if it fails. e.g. return + -EINVAL if the input is wrong. This will include the functions which will + return an address which encodes `-errno` by ERR_PTR() macro. + +EI_ETYPE_ERRNO_NULL + This function will return an `-errno` or `NULL` if it fails. If the call= er + of this function checks the return value with IS_ERR_OR_NULL() macro, th= is + type will be appropriate. + +EI_ETYPE_TRUE + This function will return `true` (non-zero positive value) if it fails. + +If you specifies a wrong type, for example, EI_TYPE_ERRNO for the function +which returns an allocated object, it may cause a problem because the retu= rned +value is not an object address and the caller can not access to the addres= s. + + How to add new fault injection capability ----------------------------------------- =20 diff --git a/include/asm-generic/error-injection.h b/include/asm-generic/er= ror-injection.h index c0b9d3217ed9..b05253f68eaa 100644 --- a/include/asm-generic/error-injection.h +++ b/include/asm-generic/error-injection.h @@ -19,8 +19,10 @@ struct pt_regs; =20 #ifdef CONFIG_FUNCTION_ERROR_INJECTION /* - * Whitelist generating macro. Specify functions which can be - * error-injectable using this macro. + * Whitelist generating macro. Specify functions which can be error-inject= able + * using this macro. If you unsure what is required for the error-injectab= le + * functions, please read Documentation/fault-injection/fault-injection.rst + * 'Error Injectable Functions' section. */ #define ALLOW_ERROR_INJECTION(fname, _etype) \ static struct error_injection_entry __used \