The patch titled
Subject: kasan: docs: update shadow memory section
has been removed from the -mm tree. Its filename was
kasan-docs-update-shadow-memory-section.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Subject: kasan: docs: update shadow memory section
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.
Link: https://lkml.kernel.org/r/00f8c38b0fd5290a3f4dced04eaba41383e67e14.1615559068.git.andreyknvl@xxxxxxxxxx
Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Reviewed-by: Marco Elver <elver@xxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/dev-tools/kasan.rst | 31 ++++++++++++----------------
1 file changed, 14 insertions(+), 17 deletions(-)
--- a/Documentation/dev-tools/kasan.rst~kasan-docs-update-shadow-memory-section
+++ a/Documentation/dev-tools/kasan.rst
@@ -313,14 +313,11 @@ 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
~~~~~~~~~~~~~~~~~
@@ -332,10 +329,9 @@ page is mapped over the shadow area. Thi
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
@@ -346,9 +342,10 @@ 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
@@ -367,10 +364,10 @@ 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
_
Patches currently in -mm which might be from andreyknvl@xxxxxxxxxx are
