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kasan: clarify HW_TAGS impact on TBI

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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 <andreyknvl@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andrey Konovalov 2021-02-24 12:05:09 -08:00 committed by Linus Torvalds
parent f00748bfa0
commit 4062c24598
1 changed files with 11 additions and 5 deletions
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16
Documentation/dev-tools/kasan.rst
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@ -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.
@ -289,6 +288,13 @@ 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?
--------------------------------------------