[PATCH v2 02/14] kasan: clarify HW_TAGS impact on TBI
From: Andrey Konovalov <hidden>
Date: 2021-01-13 16:23:03
Also in:
linux-mm, lkml
Subsystem:
documentation, documentation process, kasan, the rest · Maintainers:
Jonathan Corbet, Andrey Ryabinin, Linus Torvalds
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 Reviewed-by: Marco Elver <elver@google.com> Reviewed-by: Alexander Potapenko <glider@google.com> Signed-off-by: Andrey Konovalov <redacted> --- 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 0fc3fb1860c4..26c99852a852 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.
@@ -305,6 +304,13 @@ 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? --------------------------------------------
--
2.30.0.284.gd98b1dd5eaa7-goog
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