From: Andrey Konovalov <andreyknvl@google.com>
To: Andrew Morton <akpm@linux-foundation.org>,
Alexander Potapenko <glider@google.com>,
Marco Elver <elver@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>,
Dmitry Vyukov <dvyukov@google.com>,
kasan-dev@googlegroups.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org,
Andrey Konovalov <andreyknvl@google.com>
Subject: [PATCH v2 09/11] kasan: docs: update shadow memory section
Date: Fri, 12 Mar 2021 15:24:32 +0100 [thread overview]
Message-ID: <00f8c38b0fd5290a3f4dced04eaba41383e67e14.1615559068.git.andreyknvl@google.com> (raw)
In-Reply-To: <c2bbb56eaea80ad484f0ee85bb71959a3a63f1d7.1615559068.git.andreyknvl@google.com>
Update the "Shadow memory" section in KASAN documentation:
- Rearrange the introduction paragraph do it doesn't give a
"KASAN has an issue" impression.
- Update the list of architectures with vmalloc support.
- Punctuation, readability, and other minor clean-ups.
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
Documentation/dev-tools/kasan.rst | 31 ++++++++++++++-----------------
1 file changed, 14 insertions(+), 17 deletions(-)
diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
index 2744ae6347c6..d0c1796122df 100644
--- a/Documentation/dev-tools/kasan.rst
+++ b/Documentation/dev-tools/kasan.rst
@@ -304,14 +304,11 @@ checking gets disabled.
Shadow memory
-------------
-The kernel maps memory in a number of different parts of the address
-space. This poses something of a problem for KASAN, which requires
-that all addresses accessed by instrumented code have a valid shadow
-region.
-
-The range of kernel virtual addresses is large: there is not enough
-real memory to support a real shadow region for every address that
-could be accessed by the kernel.
+The kernel maps memory in several different parts of the address space.
+The range of kernel virtual addresses is large: there is not enough real
+memory to support a real shadow region for every address that could be
+accessed by the kernel. Therefore, KASAN only maps real shadow for certain
+parts of the address space.
Default behaviour
~~~~~~~~~~~~~~~~~
@@ -323,10 +320,9 @@ page is mapped over the shadow area. This read-only shadow page
declares all memory accesses as permitted.
This presents a problem for modules: they do not live in the linear
-mapping, but in a dedicated module space. By hooking in to the module
-allocator, KASAN can temporarily map real shadow memory to cover
-them. This allows detection of invalid accesses to module globals, for
-example.
+mapping but in a dedicated module space. By hooking into the module
+allocator, KASAN temporarily maps real shadow memory to cover them.
+This allows detection of invalid accesses to module globals, for example.
This also creates an incompatibility with ``VMAP_STACK``: if the stack
lives in vmalloc space, it will be shadowed by the read-only page, and
@@ -337,9 +333,10 @@ CONFIG_KASAN_VMALLOC
~~~~~~~~~~~~~~~~~~~~
With ``CONFIG_KASAN_VMALLOC``, KASAN can cover vmalloc space at the
-cost of greater memory usage. Currently this is only supported on x86.
+cost of greater memory usage. Currently, this is supported on x86,
+riscv, s390, and powerpc.
-This works by hooking into vmalloc and vmap, and dynamically
+This works by hooking into vmalloc and vmap and dynamically
allocating real shadow memory to back the mappings.
Most mappings in vmalloc space are small, requiring less than a full
@@ -358,10 +355,10 @@ memory.
To avoid the difficulties around swapping mappings around, KASAN expects
that the part of the shadow region that covers the vmalloc space will
-not be covered by the early shadow page, but will be left
-unmapped. This will require changes in arch-specific code.
+not be covered by the early shadow page but will be left unmapped.
+This will require changes in arch-specific code.
-This allows ``VMAP_STACK`` support on x86, and can simplify support of
+This allows ``VMAP_STACK`` support on x86 and can simplify support of
architectures that do not have a fixed module region.
For developers
--
2.31.0.rc2.261.g7f71774620-goog
next prev parent reply other threads:[~2021-03-12 14:25 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-12 14:24 [PATCH v2 01/11] kasan: docs: clean up sections Andrey Konovalov
2021-03-12 14:24 ` [PATCH v2 02/11] kasan: docs: update overview section Andrey Konovalov
2021-03-12 15:07 ` Marco Elver
2021-03-12 14:24 ` [PATCH v2 03/11] kasan: docs: update usage section Andrey Konovalov
2021-03-12 15:07 ` Marco Elver
2021-03-12 14:24 ` [PATCH v2 04/11] kasan: docs: update error reports section Andrey Konovalov
2021-03-12 15:08 ` Marco Elver
2021-03-12 14:24 ` [PATCH v2 05/11] kasan: docs: update boot parameters section Andrey Konovalov
2021-03-12 15:08 ` Marco Elver
2021-03-12 14:24 ` [PATCH v2 06/11] kasan: docs: update GENERIC implementation details section Andrey Konovalov
2021-03-12 15:08 ` Marco Elver
2021-03-12 14:24 ` [PATCH v2 07/11] kasan: docs: update SW_TAGS " Andrey Konovalov
2021-03-12 15:09 ` Marco Elver
2021-03-12 14:24 ` [PATCH v2 08/11] kasan: docs: update HW_TAGS " Andrey Konovalov
2021-03-12 15:09 ` Marco Elver
2021-03-12 14:24 ` Andrey Konovalov [this message]
2021-03-12 15:09 ` [PATCH v2 09/11] kasan: docs: update shadow memory section Marco Elver
2021-03-12 14:24 ` [PATCH v2 10/11] kasan: docs: update ignoring accesses section Andrey Konovalov
2021-03-12 15:10 ` Marco Elver
2021-03-12 14:24 ` [PATCH v2 11/11] kasan: docs: update tests section Andrey Konovalov
2021-03-12 15:11 ` Marco Elver
2021-03-12 15:06 ` [PATCH v2 01/11] kasan: docs: clean up sections Marco Elver
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