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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). 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 In the report above the arrows point to the shadow byte 03, which means that
the accessed address is partially accessible. the accessed address is partially accessible. For tag-based KASAN modes this
last report section shows the memory tags around the accessed address
For tag-based KASAN this last report section shows the memory tags around the (see the `Implementation details`_ section).
accessed address (see `Implementation details`_ section).
Boot parameters 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 intended for use in production as a security mitigation. Therefore it supports
boot parameters that allow to disable KASAN competely or otherwise control boot parameters that allow to disable KASAN competely or otherwise control
particular KASAN features. particular KASAN features.
@@ -289,6 +288,13 @@ reserved to tag freed memory regions.
Hardware tag-based KASAN currently only supports tagging of Hardware tag-based KASAN currently only supports tagging of
kmem_cache_alloc/kmalloc and page_alloc memory. 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? What memory accesses are sanitised by KASAN?
-------------------------------------------- --------------------------------------------