From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 26C3DC43460 for ; Fri, 30 Apr 2021 06:00:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0CEFE61483 for ; Fri, 30 Apr 2021 06:00:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229609AbhD3GBP (ORCPT ); Fri, 30 Apr 2021 02:01:15 -0400 Received: from mail.kernel.org ([198.145.29.99]:54436 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230318AbhD3GBM (ORCPT ); Fri, 30 Apr 2021 02:01:12 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 2ED8C6148E; Fri, 30 Apr 2021 06:00:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1619762422; bh=xDnPQk/EgYDX4dPLLMCy+no7XcCLPZoRFn2dl459wCY=; h=Date:From:To:Subject:In-Reply-To:From; b=rl8iqTYiEvum/Byy/9n1LCNh20eW5zOwaEAct2/9Rz/8YFU8FNBEbVXuX/cJ089hj Yi1lYOlIVOgLYqVuOz6oV7gr8kgsnEyBkR20RlnwfC9mTr1hQdlM5KyhTQerJaRXaY v/GfNOWe69VApmSfDNPL3O0JbTMzHo/CLauwTfmc= Date: Thu, 29 Apr 2021 23:00:21 -0700 From: Andrew Morton To: akpm@linux-foundation.org, andreyknvl@google.com, aryabinin@virtuozzo.com, dvyukov@google.com, elver@google.com, glider@google.com, linux-mm@kvack.org, mm-commits@vger.kernel.org, torvalds@linux-foundation.org Subject: [patch 139/178] kasan: docs: update error reports section Message-ID: <20210430060021.Rfma7nv46%akpm@linux-foundation.org> In-Reply-To: <20210429225251.02b6386d21b69255b4f6c163@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org From: Andrey Konovalov Subject: kasan: docs: update error reports section Update the "Error reports" section in KASAN documentation: - Mention that bug titles are best-effort. - Move and reword the part about auxiliary stacks from "Implementation details". - Punctuation, readability, and other minor clean-ups. Link: https://lkml.kernel.org/r/3531e8fe6972cf39d1954e3643237b19eb21227e.1615559068.git.andreyknvl@google.com Signed-off-by: Andrey Konovalov Reviewed-by: Marco Elver Cc: Alexander Potapenko Cc: Andrey Ryabinin Cc: Dmitry Vyukov Signed-off-by: Andrew Morton --- Documentation/dev-tools/kasan.rst | 46 +++++++++++++++------------- 1 file changed, 26 insertions(+), 20 deletions(-) --- a/Documentation/dev-tools/kasan.rst~kasan-docs-update-error-reports-section +++ a/Documentation/dev-tools/kasan.rst @@ -60,7 +60,7 @@ physical pages, enable ``CONFIG_PAGE_OWN Error reports ~~~~~~~~~~~~~ -A typical out-of-bounds access generic KASAN report looks like this:: +A typical KASAN report looks like this:: ================================================================== BUG: KASAN: slab-out-of-bounds in kmalloc_oob_right+0xa8/0xbc [test_kasan] @@ -133,33 +133,43 @@ A typical out-of-bounds access generic K ffff8801f44ec400: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ================================================================== -The header of the report provides a short summary of what kind of bug happened -and what kind of access caused it. It's followed by a stack trace of the bad -access, a stack trace of where the accessed memory was allocated (in case bad -access happens on a slab object), and a stack trace of where the object was -freed (in case of a use-after-free bug report). Next comes a description of -the accessed slab object and information about the accessed memory page. +The report header summarizes what kind of bug happened and what kind of access +caused it. It is followed by a stack trace of the bad access, a stack trace of +where the accessed memory was allocated (in case a slab object was accessed), +and a stack trace of where the object was freed (in case of a use-after-free +bug report). Next comes a description of the accessed slab object and the +information about the accessed memory page. -In the last section the report shows memory state around the accessed address. -Internally KASAN tracks memory state separately for each memory granule, which +In the end, the report shows the memory state around the accessed address. +Internally, KASAN tracks memory state separately for each memory granule, which is either 8 or 16 aligned bytes depending on KASAN mode. Each number in the memory state section of the report shows the state of one of the memory granules that surround the accessed address. -For generic KASAN the size of each memory granule is 8. The state of each +For generic KASAN, the size of each memory granule is 8. The state of each granule is encoded in one shadow byte. Those 8 bytes can be accessible, -partially accessible, freed or be a part of a redzone. KASAN uses the following -encoding for each shadow byte: 0 means that all 8 bytes of the corresponding +partially accessible, freed, or be a part of a redzone. KASAN uses the following +encoding for each shadow byte: 00 means that all 8 bytes of the corresponding memory region are accessible; number N (1 <= N <= 7) means that the first N bytes are accessible, and other (8 - N) bytes are not; any negative value indicates that the entire 8-byte word is inaccessible. KASAN uses different negative values to distinguish between different kinds of inaccessible memory like redzones or freed memory (see mm/kasan/kasan.h). -In the report above the arrows point to the shadow byte 03, which means that -the accessed address is partially accessible. For tag-based KASAN modes this -last report section shows the memory tags around the accessed address -(see the `Implementation details`_ section). +In the report above, the arrow points to the shadow byte ``03``, which means +that the accessed address is partially accessible. + +For tag-based KASAN modes, this last report section shows the memory tags around +the accessed address (see the `Implementation details`_ section). + +Note that KASAN bug titles (like ``slab-out-of-bounds`` or ``use-after-free``) +are best-effort: KASAN prints the most probable bug type based on the limited +information it has. The actual type of the bug might be different. + +Generic KASAN also reports up to two auxiliary call stack traces. These stack +traces point to places in code that interacted with the object but that are not +directly present in the bad access stack trace. Currently, this includes +call_rcu() and workqueue queuing. Boot parameters ~~~~~~~~~~~~~~~ @@ -223,10 +233,6 @@ function calls GCC directly inserts the This option significantly enlarges kernel but it gives x1.1-x2 performance boost over outline instrumented kernel. -Generic KASAN also reports the last 2 call stacks to creation of work that -potentially has access to an object. Call stacks for the following are shown: -call_rcu() and workqueue queuing. - Generic KASAN is the only mode that delays the reuse of freed object via quarantine (see mm/kasan/quarantine.c for implementation). _