[v3,00/16] x86: Add support for Clang CFI

Message

Sami Tolvanen Sept. 14, 2021, 7:10 p.m. UTC

This series adds support for Clang's Control-Flow Integrity (CFI)
checking to x86_64. With CFI, the compiler injects a runtime
check before each indirect function call to ensure the target is
a valid function with the correct static type. This restricts
possible call targets and makes it more difficult for an attacker
to exploit bugs that allow the modification of stored function
pointers. For more details, see:

  https://clang.llvm.org/docs/ControlFlowIntegrity.html

The first two patches contain objtool support for CFI, the
remaining patches change function declarations to use opaque
types, fix type mismatch issues that confuse the compiler, and
disable CFI where it can't be used.

You can also pull this series from

  https://github.com/samitolvanen/linux.git x86-cfi-v3

---
Changes in v3:
- Dropped Clang requirement to >= 13 after the missing compiler
  fix was backported there.

- Added DEFINE_CFI_IMMEDIATE_RETURN_STUB to address the issue
  with tp_stub_func in kernel/tracepoint.c.

- Renamed asm_func_t to asm_func_ptr.

- Changed extable handlers to use __cficanonical instead of
  disabling CFI for fixup_exception.


Changes in v2:
- Dropped the first objtool patch as the warnings were fixed in
  separate patches.

- Changed fix_cfi_relocs() in objtool to not rely on jump table
  symbols, and to return an error if it can't find a relocation.

- Fixed a build issue with ASM_STACK_FRAME_NON_STANDARD().

- Dropped workarounds for inline assembly references to
  address-taken static functions with CFI as this was fixed in
  the compiler.

- Changed the C declarations of non-callable functions to use
  opaque types and dropped the function_nocfi() patches.

- Changed ARCH_SUPPORTS_CFI_CLANG to depend on Clang >=14 for
  the compiler fixes.


Kees Cook (1):
  x86, relocs: Ignore __typeid__ relocations

Sami Tolvanen (15):
  objtool: Add CONFIG_CFI_CLANG support
  objtool: Add ASM_STACK_FRAME_NON_STANDARD
  linkage: Add DECLARE_ASM_FUNC_SYMBOL
  cfi: Add DEFINE_CFI_IMMEDIATE_RETURN_STUB
  tracepoint: Exclude tp_stub_func from CFI checking
  ftrace: Use an opaque type for functions not callable from C
  lkdtm: Disable UNSET_SMEP with CFI
  lkdtm: Use an opaque type for lkdtm_rodata_do_nothing
  x86: Use an opaque type for functions not callable from C
  x86/extable: Mark handlers __cficanonical
  x86/purgatory: Disable CFI
  x86, module: Ignore __typeid__ relocations
  x86, cpu: Use LTO for cpu.c with CFI
  x86, kprobes: Fix optprobe_template_func type mismatch
  x86, build: Allow CONFIG_CFI_CLANG to be selected

 arch/x86/Kconfig                      |  1 +
 arch/x86/include/asm/ftrace.h         |  2 +-
 arch/x86/include/asm/idtentry.h       | 10 ++---
 arch/x86/include/asm/page_64.h        |  7 +--
 arch/x86/include/asm/paravirt_types.h |  3 +-
 arch/x86/include/asm/processor.h      |  2 +-
 arch/x86/include/asm/proto.h          | 25 ++++++-----
 arch/x86/include/asm/uaccess_64.h     |  9 ++--
 arch/x86/kernel/alternative.c         |  2 +-
 arch/x86/kernel/ftrace.c              |  2 +-
 arch/x86/kernel/kprobes/opt.c         |  4 +-
 arch/x86/kernel/module.c              |  4 ++
 arch/x86/kernel/paravirt.c            |  4 +-
 arch/x86/kvm/emulate.c                |  4 +-
 arch/x86/kvm/kvm_emulate.h            |  9 +---
 arch/x86/mm/extable.c                 | 64 +++++++++++++++------------
 arch/x86/power/Makefile               |  2 +
 arch/x86/purgatory/Makefile           |  2 +-
 arch/x86/tools/relocs.c               |  7 +++
 arch/x86/xen/enlighten_pv.c           |  6 +--
 arch/x86/xen/xen-ops.h                | 10 ++---
 drivers/misc/lkdtm/bugs.c             |  2 +-
 drivers/misc/lkdtm/lkdtm.h            |  2 +-
 drivers/misc/lkdtm/perms.c            |  2 +-
 drivers/misc/lkdtm/rodata.c           |  2 +-
 include/asm-generic/vmlinux.lds.h     | 11 +++++
 include/linux/cfi.h                   | 14 ++++++
 include/linux/ftrace.h                |  7 +--
 include/linux/linkage.h               | 13 ++++++
 include/linux/objtool.h               |  6 +++
 kernel/cfi.c                          | 24 +++++++++-
 kernel/tracepoint.c                   |  5 +--
 tools/include/linux/objtool.h         |  6 +++
 tools/objtool/arch/x86/decode.c       | 16 +++++++
 tools/objtool/elf.c                   | 51 +++++++++++++++++++++
 tools/objtool/include/objtool/arch.h  |  3 ++
 tools/objtool/include/objtool/elf.h   |  2 +-
 37 files changed, 250 insertions(+), 95 deletions(-)


base-commit: d0ee23f9d78be5531c4b055ea424ed0b489dfe9b