[PATCH v10 0/5] kasan: support backing vmalloc space with real shadow memory

[Daniel Axtens <dja@axtens.net>]

Currently, vmalloc space is backed by the early shadow page. This
means that kasan is incompatible with VMAP_STACK.

This series provides a mechanism to back vmalloc space with real,
dynamically allocated memory. I have only wired up x86, because that's
the only currently supported arch I can work with easily, but it's
very easy to wire up other architectures, and it appears that there is
some work-in-progress code to do this on arm64 and s390.

This has been discussed before in the context of VMAP_STACK:
 - https://bugzilla.kernel.org/show_bug.cgi?id=202009
 - https://lkml.org/lkml/2018/7/22/198
 - https://lkml.org/lkml/2019/7/19/822

In terms of implementation details:

Most mappings in vmalloc space are small, requiring less than a full
page of shadow space. Allocating a full shadow page per mapping would
therefore be wasteful. Furthermore, to ensure that different mappings
use different shadow pages, mappings would have to be aligned to
KASAN_SHADOW_SCALE_SIZE * PAGE_SIZE.

Instead, share backing space across multiple mappings. Allocate a
backing page when a mapping in vmalloc space uses a particular page of
the shadow region. This page can be shared by other vmalloc mappings
later on.

We hook in to the vmap infrastructure to lazily clean up unused shadow
memory.

Daniel Axtens (5):
  kasan: support backing vmalloc space with real shadow memory
  kasan: add test for vmalloc
  fork: support VMAP_STACK with KASAN_VMALLOC
  x86/kasan: support KASAN_VMALLOC
  kasan debug: track pages allocated for vmalloc shadow

 Documentation/dev-tools/kasan.rst |  63 ++++++++
 arch/Kconfig                      |   9 +-
 arch/x86/Kconfig                  |   1 +
 arch/x86/mm/kasan_init_64.c       |  60 +++++++
 include/linux/kasan.h             |  31 ++++
 include/linux/moduleloader.h      |   2 +-
 include/linux/vmalloc.h           |  12 ++
 kernel/fork.c                     |   4 +
 lib/Kconfig.kasan                 |  16 ++
 lib/test_kasan.c                  |  26 +++
 mm/kasan/common.c                 | 254 ++++++++++++++++++++++++++++++
 mm/kasan/generic_report.c         |   3 +
 mm/kasan/kasan.h                  |   1 +
 mm/vmalloc.c                      |  53 ++++++-
 14 files changed, 522 insertions(+), 13 deletions(-)

-- 
2.20.1