From 13b4c0d80cb2dd2951f9d5936177bca14e72d3d9 Mon Sep 17 00:00:00 2001 From: Andrey Konovalov Date: Wed, 3 Feb 2021 15:34:59 +1100 Subject: [PATCH] FROMGIT: kasan: clarify HW_TAGS impact on TBI Mention in the documentation that enabling CONFIG_KASAN_HW_TAGS always results in in-kernel TBI (Top Byte Ignore) being enabled. Also do a few minor documentation cleanups. Link: https://linux-review.googlesource.com/id/Iba2a6697e3c6304cb53f89ec61dedc77fa29e3ae Link: https://lkml.kernel.org/r/3b4ea6875bb14d312092ad14ac55cb456c83c08e.1610733117.git.andreyknvl@google.com Signed-off-by: Andrey Konovalov Reviewed-by: Marco Elver Reviewed-by: Alexander Potapenko Cc: Andrey Ryabinin Cc: Branislav Rankov Cc: Catalin Marinas Cc: Dmitry Vyukov Cc: Evgenii Stepanov Cc: Kevin Brodsky Cc: Peter Collingbourne Cc: Vincenzo Frascino Cc: Will Deacon Signed-off-by: Andrew Morton Signed-off-by: Stephen Rothwell (cherry picked from commit 0365c6f8454dde0769dc0bb4863e20852d6a458b https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git akpm) Bug: 172318110 Signed-off-by: Andrey Konovalov Change-Id: I6c2c7fa01e0b22178ca175f0fbba1e1705144f39 --- Documentation/dev-tools/kasan.rst | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-) diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst index 964e71539efa..e87953ed7147 100644 --- a/Documentation/dev-tools/kasan.rst +++ b/Documentation/dev-tools/kasan.rst @@ -147,15 +147,14 @@ 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 this last report section shows the memory tags around the -accessed address (see `Implementation details`_ section). +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). Boot parameters ~~~~~~~~~~~~~~~ -Hardware tag-based KASAN mode (see the section about different mode below) is +Hardware tag-based KASAN mode (see the section about various modes below) is intended for use in production as a security mitigation. Therefore it supports boot parameters that allow to disable KASAN competely or otherwise control particular KASAN features. @@ -290,6 +289,13 @@ reserved to tag freed memory regions. Hardware tag-based KASAN currently only supports tagging of kmem_cache_alloc/kmalloc and page_alloc memory. +If the hardware doesn't support MTE (pre ARMv8.5), hardware tag-based KASAN +won't be enabled. In this case all boot parameters are ignored. + +Note, that enabling CONFIG_KASAN_HW_TAGS always results in in-kernel TBI being +enabled. Even when kasan.mode=off is provided, or when the hardware doesn't +support MTE (but supports TBI). + What memory accesses are sanitised by KASAN? --------------------------------------------