[PATCH v4 0/1] Seal system mappings

[jeffxu@chromium.org]

From: Jeff Xu <jeffxu@chromium.org>

Seal vdso, vvar, sigpage, uprobes and vsyscall.

Those mappings are readonly or executable only, sealing can protect
them from ever changing or unmapped during the life time of the process.
For complete descriptions of memory sealing, please see mseal.rst [1].

System mappings such as vdso, vvar, and sigpage (for arm) are
generated by the kernel during program initialization, and are
sealed after creation.

Unlike the aforementioned mappings, the uprobe mapping is not
established during program startup. However, its lifetime is the same
as the process's lifetime [2]. It is sealed from creation.

The vdso, vvar, sigpage, and uprobe mappings all invoke the
_install_special_mapping() function. As no other mappings utilize this
function, it is logical to incorporate sealing logic within
_install_special_mapping(). This approach avoids the necessity of
modifying code across various architecture-specific implementations.

The vsyscall mapping, which has its own initialization function, is
sealed in the XONLY case, it seems to be the most common and secure
case of using vsyscall.

It is important to note that the CHECKPOINT_RESTORE feature (CRIU) may
alter the mapping of vdso, vvar, and sigpage during restore
operations. Consequently, this feature cannot be universally enabled
across all systems.

Currently, memory sealing is only functional in a 64-bit kernel
configuration.

To enable this feature, the architecture needs to be tested to
confirm that it doesn't unmap/remap system mappings during the
the life time of the process. After the architecture enables
ARCH_HAS_SEAL_SYSTEM_MAPPINGS, a distribution can set
CONFIG_SEAL_SYSTEM_MAPPING to manage access to the feature.
Alternatively, kernel command line (exec.seal_system_mappings)
enables this feature also.

This feature is tested using ChromeOS and Android on X86_64 and ARM64,
therefore ARCH_HAS_SEAL_SYSTEM_MAPPINGS is set for X86_64 and ARM64.
Other architectures can enable this after testing. No specific hardware
features from the CPU are needed.

This feature's security enhancements will benefit ChromeOS, Android,
and other secure-by-default systems.

[1] Documentation/userspace-api/mseal.rst
[2] https://lore.kernel.org/all/CABi2SkU9BRUnqf70-nksuMCQ+yyiWjo3fM4XkRkL-NrCZxYAyg@mail.gmail.com/

History:
V4:
  ARCH_HAS_SEAL_SYSTEM_MAPPINGS (Lorenzo Stoakes)
  test info (Lorenzo Stoakes)
  Update  mseal.rst (Liam R. Howlett)
  Update test_mremap_vdso.c (Liam R. Howlett)
  Misc. style, comments, doc update (Liam R. Howlett)

V3:
  https://lore.kernel.org/all/20241113191602.3541870-1-jeffxu@google.com/
  Revert uprobe to v1 logic (Oleg Nesterov)
  use CONFIG_SEAL_SYSTEM_MAPPINGS instead of _ALWAYS/_NEVER (Kees Cook)
  Move kernel cmd line from fs/exec.c to mm/mseal.c and misc. refactor (Liam R. Howlett)

V2:
  https://lore.kernel.org/all/20241014215022.68530-1-jeffxu@google.com/
  Seal uprobe always (Oleg Nesterov)
  Update comments and description (Randy Dunlap, Liam R.Howlett, Oleg Nesterov)
  Rebase to linux_main

V1:
https://lore.kernel.org/all/20241004163155.3493183-1-jeffxu@google.com/

Jeff Xu (1):
  exec: seal system mappings

 .../admin-guide/kernel-parameters.txt         | 11 ++++++
 Documentation/userspace-api/mseal.rst         |  4 ++
 arch/arm64/Kconfig                            |  1 +
 arch/x86/Kconfig                              |  1 +
 arch/x86/entry/vsyscall/vsyscall_64.c         |  8 +++-
 include/linux/mm.h                            | 12 ++++++
 init/Kconfig                                  | 25 ++++++++++++
 mm/mmap.c                                     | 10 +++++
 mm/mseal.c                                    | 39 +++++++++++++++++++
 security/Kconfig                              | 24 ++++++++++++
 10 files changed, 133 insertions(+), 2 deletions(-)

-- 
2.47.0.338.g60cca15819-goog