| Message ID | c0f6a95b0fa59ce0ef502f4ea11522141e3c8faf.1615498565.git.andreyknvl@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [01/11] kasan: docs: clean up sections | expand |
On Thu, Mar 11, 2021 at 10:37PM +0100, Andrey Konovalov wrote: [...] > +Other parts of the kernel might access metadata for allocated objects. Normally, > +KASAN detects and reports such accesses, but in certain cases (e.g., in memory > +allocators) these accesses are valid. Disabling instrumentation for memory > +allocators files helps with accesses that happen directly in that code for > +software KASAN modes. But it does not help when the accesses happen indirectly > +(through generic function calls) or with the hardware tag-based mode that does > +not use compiler instrumentation. > + > +To disable KASAN reports in a certain part of the kernel code: > + > +- For software modes, add a > + ``kasan_disable_current()``/``kasan_enable_current()`` critical section. Should we mention function attribute __no_sanitize_address (and noinstr, which just applies to any kind of instrumentation) here? Perhaps with the note that called functions may still be instrumented, and in such cases would require combining with kasan_{disable,enable}_current(). > +- For tag-based modes, use ``kasan_reset_tag()`` or ``page_kasan_tag_reset()``.
On Fri, Mar 12, 2021 at 12:02 PM Marco Elver <elver@google.com> wrote: > > On Thu, Mar 11, 2021 at 10:37PM +0100, Andrey Konovalov wrote: > [...] > > +Other parts of the kernel might access metadata for allocated objects. Normally, > > +KASAN detects and reports such accesses, but in certain cases (e.g., in memory > > +allocators) these accesses are valid. Disabling instrumentation for memory > > +allocators files helps with accesses that happen directly in that code for > > +software KASAN modes. But it does not help when the accesses happen indirectly > > +(through generic function calls) or with the hardware tag-based mode that does > > +not use compiler instrumentation. > > + > > +To disable KASAN reports in a certain part of the kernel code: > > + > > +- For software modes, add a > > + ``kasan_disable_current()``/``kasan_enable_current()`` critical section. > > Should we mention function attribute __no_sanitize_address (and noinstr, > which just applies to any kind of instrumentation) here? Perhaps with > the note that called functions may still be instrumented, and in such > cases would require combining with kasan_{disable,enable}_current(). Indeed, forgot about the attributes.. Will add, thank you!
diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst index 2b61d90e136f..6628b133c9ad 100644 --- a/Documentation/dev-tools/kasan.rst +++ b/Documentation/dev-tools/kasan.rst @@ -368,7 +368,7 @@ Ignoring accesses ~~~~~~~~~~~~~~~~~ Software KASAN modes use compiler instrumentation to insert validity checks. -Such instrumentation might be incompatible with some part of the kernel, and +Such instrumentation might be incompatible with some parts of the kernel, and therefore needs to be disabled. To disable instrumentation for specific files or directories, add a line similar to the following to the respective kernel Makefile: @@ -381,6 +381,19 @@ Makefile: KASAN_SANITIZE := n +Other parts of the kernel might access metadata for allocated objects. Normally, +KASAN detects and reports such accesses, but in certain cases (e.g., in memory +allocators) these accesses are valid. Disabling instrumentation for memory +allocators files helps with accesses that happen directly in that code for +software KASAN modes. But it does not help when the accesses happen indirectly +(through generic function calls) or with the hardware tag-based mode that does +not use compiler instrumentation. + +To disable KASAN reports in a certain part of the kernel code: + +- For software modes, add a + ``kasan_disable_current()``/``kasan_enable_current()`` critical section. +- For tag-based modes, use ``kasan_reset_tag()`` or ``page_kasan_tag_reset()``. Tests ~~~~~
Update the "Ignoring accesses" section in KASAN documentation: - Mention kasan_disable/enable_current(). - Mention kasan_reset_tag()/page_kasan_tag_reset(). - A punctuation clean-up. Signed-off-by: Andrey Konovalov <andreyknvl@google.com> --- Documentation/dev-tools/kasan.rst | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-)