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=-15.8 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 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 D7531C433ED for ; Fri, 30 Apr 2021 06:01:31 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 88F8561482 for ; Fri, 30 Apr 2021 06:01:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 88F8561482 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 24EEF94003F; Fri, 30 Apr 2021 02:01:30 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 1D7D8940038; Fri, 30 Apr 2021 02:01:30 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 02C4294003F; Fri, 30 Apr 2021 02:01:29 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0211.hostedemail.com [216.40.44.211]) by kanga.kvack.org (Postfix) with ESMTP id D1FCA940038 for ; Fri, 30 Apr 2021 02:01:29 -0400 (EDT) Received: from smtpin26.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 99E4B249F for ; Fri, 30 Apr 2021 06:01:29 +0000 (UTC) X-FDA: 78087986298.26.9F4A253 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf13.hostedemail.com (Postfix) with ESMTP id EAC0FE002020 for ; Fri, 30 Apr 2021 06:00:19 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 1906D61481; Fri, 30 Apr 2021 06:00:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1619762428; bh=2NTzOym+sSDT/Bef7OscGQqUmw/U8pYrdm8XldiKhuU=; h=Date:From:To:Subject:In-Reply-To:From; b=rKo5qjbWiE6uPSc939AWC89WL8dwCpWNyeOB0dXJz1C/U0IQ81wUc+713i7X1fId1 YY4i0hZHm5yqVqCoigOW8a1Fst/GfCRox6wTocoQWe8ih1fpiNya6RwiLrgt0zYviX lrAD469xifxPCUhgeQZ8Fek4/+D1OsL11+ht5AMw= Date: Thu, 29 Apr 2021 23:00:27 -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 141/178] kasan: docs: update GENERIC implementation details section Message-ID: <20210430060027.tUSBKxSC2%akpm@linux-foundation.org> In-Reply-To: <20210429225251.02b6386d21b69255b4f6c163@linux-foundation.org> User-Agent: s-nail v14.8.16 Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=rKo5qjbW; dmarc=none; spf=pass (imf13.hostedemail.com: domain of akpm@linux-foundation.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org X-Rspamd-Server: rspam03 X-Stat-Signature: bqaj1swyzcrbw1bthdp1m3teijwpng6m X-Rspamd-Queue-Id: EAC0FE002020 Received-SPF: none (linux-foundation.org>: No applicable sender policy available) receiver=imf13; identity=mailfrom; envelope-from=""; helo=mail.kernel.org; client-ip=198.145.29.99 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1619762419-952586 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Andrey Konovalov Subject: kasan: docs: update GENERIC implementation details section Update the "Implementation details" section for generic KASAN: - Don't mention kmemcheck, it's not present in the kernel anymore. - Don't mention GCC as the only supported compiler. - Update kasan_mem_to_shadow() definition to match actual code. - Punctuation, readability, and other minor clean-ups. Link: https://lkml.kernel.org/r/f2f35fdab701f8c709f63d328f98aec2982c8acc.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 | 29 +++++++++++++--------------- 1 file changed, 14 insertions(+), 15 deletions(-) --- a/Documentation/dev-tools/kasan.rst~kasan-docs-update-generic-implementation-details-section +++ a/Documentation/dev-tools/kasan.rst @@ -209,12 +209,11 @@ Implementation details Generic KASAN ~~~~~~~~~~~~~ -From a high level perspective, KASAN's approach to memory error detection is -similar to that of kmemcheck: use shadow memory to record whether each byte of -memory is safe to access, and use compile-time instrumentation to insert checks -of shadow memory on each memory access. +Software KASAN modes use shadow memory to record whether each byte of memory is +safe to access and use compile-time instrumentation to insert shadow memory +checks before each memory access. -Generic KASAN dedicates 1/8th of kernel memory to its shadow memory (e.g. 16TB +Generic KASAN dedicates 1/8th of kernel memory to its shadow memory (16TB to cover 128TB on x86_64) and uses direct mapping with a scale and offset to translate a memory address to its corresponding shadow address. @@ -223,23 +222,23 @@ address:: static inline void *kasan_mem_to_shadow(const void *addr) { - return ((unsigned long)addr >> KASAN_SHADOW_SCALE_SHIFT) + return (void *)((unsigned long)addr >> KASAN_SHADOW_SCALE_SHIFT) + KASAN_SHADOW_OFFSET; } where ``KASAN_SHADOW_SCALE_SHIFT = 3``. Compile-time instrumentation is used to insert memory access checks. Compiler -inserts function calls (__asan_load*(addr), __asan_store*(addr)) before each -memory access of size 1, 2, 4, 8 or 16. These functions check whether memory -access is valid or not by checking corresponding shadow memory. - -GCC 5.0 has possibility to perform inline instrumentation. Instead of making -function calls GCC directly inserts the code to check the shadow memory. -This option significantly enlarges kernel but it gives x1.1-x2 performance -boost over outline instrumented kernel. +inserts function calls (``__asan_load*(addr)``, ``__asan_store*(addr)``) before +each memory access of size 1, 2, 4, 8, or 16. These functions check whether +memory accesses are valid or not by checking corresponding shadow memory. + +With inline instrumentation, instead of making function calls, the compiler +directly inserts the code to check shadow memory. This option significantly +enlarges the kernel, but it gives an x1.1-x2 performance boost over the +outline-instrumented kernel. -Generic KASAN is the only mode that delays the reuse of freed object via +Generic KASAN is the only mode that delays the reuse of freed objects via quarantine (see mm/kasan/quarantine.c for implementation). Software tag-based KASAN _