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author | Andrey Konovalov <andreyknvl@google.com> | 2021-04-30 08:00:36 +0200 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2021-04-30 20:20:42 +0200 |
commit | 67ca1c0b74463a7b961bb34c213b37be0deb0ab6 (patch) | |
tree | 24f9863539d678e9ae45f2e904320e2653f7e3d0 /Documentation/dev-tools/kasan.rst | |
parent | kasan: docs: update HW_TAGS implementation details section (diff) | |
download | linux-67ca1c0b74463a7b961bb34c213b37be0deb0ab6.tar.xz linux-67ca1c0b74463a7b961bb34c213b37be0deb0ab6.zip |
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@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/dev-tools/kasan.rst')
-rw-r--r-- | Documentation/dev-tools/kasan.rst | 31 |
1 files changed, 14 insertions, 17 deletions
diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst index f0dd0eaa9cde..894fc8eb374d 100644 --- a/Documentation/dev-tools/kasan.rst +++ b/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. 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 @@ -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 |