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=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL 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 C15C9C4332D for ; Fri, 12 Mar 2021 14:25:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A55086501B for ; Fri, 12 Mar 2021 14:25:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232262AbhCLOZC (ORCPT ); Fri, 12 Mar 2021 09:25:02 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58094 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231766AbhCLOYv (ORCPT ); Fri, 12 Mar 2021 09:24:51 -0500 Received: from mail-wm1-x349.google.com (mail-wm1-x349.google.com [IPv6:2a00:1450:4864:20::349]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8A847C061574 for ; Fri, 12 Mar 2021 06:24:51 -0800 (PST) Received: by mail-wm1-x349.google.com with SMTP id j8so2103526wmq.6 for ; Fri, 12 Mar 2021 06:24:51 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=Ma9yDdtcKZ7wj/wPd+7FYcq2cw0HWN/l0auDvo6fPoI=; b=JVujzVqwjIYG5j1fOwr25Xh074MUoX63HHSyCm4wfG799oatexCqqAEE2xXAea9aKV Sjra9aPL3ppOOBgD48RZymsvzU9nFwGbIzQLilkW1cfVorxpDqi0v7/8Odj/B6raoZCe Scw/ef0F/cvt2H5lL+6GV463RBcGceF6rjhHt7rF54QQGq0Kk7/drKuZW58sz4h9DO7S V0enC41jV+KCMwRg7y1Sp9HhExnZsVSWQgstR99ieSIHLgg3+KoyRngQTkQNfet5LrtD WzrSev9UUXZRVjf4Xsf4sh0x01A29B6HUcXQD6dui2WloqW/laJ5aDsrP3yYaH8LJMmH UnsA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=Ma9yDdtcKZ7wj/wPd+7FYcq2cw0HWN/l0auDvo6fPoI=; b=JDq1sJHxQETOxlWbWquMMoS5rRnCbUJwmpakyz/T/WuG1VHfe7i4WLndFVH6fzKDfB Su2WjWxqIKIGTYE849s+gxqN9hkPXjbhUDIKRwdxEpfP7tI7wYwjrEWFd32h3+nJL9YD pe2AiewImlU0DmxAcjFeGPyg9LwINJoGeCDM2Z5TkKsPANvylomi1WC6SHhlA8UfJUeu 8zBjZqxlJaPxex8LuJXYX3dfe34lENAoMW37sjg+vaeQw4PiCNJ0ExfR7uwrpssZT3Kz zQsLciGnTr3AHgL8PzluLsA+9/hcYB+QuAyQFrgFZAyY/lrdB7aUx8GslyszQttzjmTp MjsQ== X-Gm-Message-State: AOAM533P72yXh7GCw1GWS0sw8WqjSVYgigknLdvGo5fAz18x+NlkSyfW uuZlT5aOxjTcBugLiECt7TLDogH5Ipfg+5dp X-Google-Smtp-Source: ABdhPJwaKyRxEHXnKrGDm4FLh1hRB4szO2CA0EyxO4FBmwgHO0zof9NcJRq+qtcFPr9FhhMMmwpZJhu4/UhptLB9 X-Received: from andreyknvl3.muc.corp.google.com ([2a00:79e0:15:13:95a:d8a8:4925:42be]) (user=andreyknvl job=sendgmr) by 2002:a7b:c18e:: with SMTP id y14mr2248623wmi.1.1615559089958; Fri, 12 Mar 2021 06:24:49 -0800 (PST) Date: Fri, 12 Mar 2021 15:24:29 +0100 In-Reply-To: Message-Id: Mime-Version: 1.0 References: X-Mailer: git-send-email 2.31.0.rc2.261.g7f71774620-goog Subject: [PATCH v2 06/11] kasan: docs: update GENERIC implementation details section From: Andrey Konovalov To: Andrew Morton , Alexander Potapenko , Marco Elver Cc: Andrey Ryabinin , Dmitry Vyukov , kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrey Konovalov Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Signed-off-by: Andrey Konovalov --- Documentation/dev-tools/kasan.rst | 27 +++++++++++++-------------- 1 file changed, 13 insertions(+), 14 deletions(-) diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst index 1189be9b4cb5..986410bf269f 100644 --- a/Documentation/dev-tools/kasan.rst +++ b/Documentation/dev-tools/kasan.rst @@ -200,12 +200,11 @@ 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. @@ -214,23 +213,23 @@ 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. +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. -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. +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 -- 2.31.0.rc2.261.g7f71774620-goog