[v8,00/40] Shadow stacks for userspace

Message

Edgecombe, Rick P March 19, 2023, 12:14 a.m. UTC

Hi,

This series implements Shadow Stacks for userspace using x86's Control-flow 
Enforcement Technology (CET). CET consists of two related security features: 
shadow stacks and indirect branch tracking. This series implements just the 
shadow stack part of this feature, and just for userspace.

The main use case for shadow stack is providing protection against return 
oriented programming attacks. It works by maintaining a secondary (shadow) 
stack using a special memory type that has protections against modification. 
When executing a CALL instruction, the processor pushes the return address to 
both the normal stack and to the special permission shadow stack. Upon RET, 
the processor pops the shadow stack copy and compares it to the normal stack 
copy. For more details, see the coverletter from v1 [0].

The comments on the last version were mainly code style and verbiage. There was 
also some late but great questions on the overall design, raised by people 
starting to look at implementing non-x86 shadow stack features. After discussion
on the history and purpose of the design choices, the changes that ultimately
came out of the discussion were documentation updates. Some of the concerns 
were eventually found to be based on misunderstandings of the x86 shadow stack 
HW limitations. Others were taken as future enhancements. There was a fair 
amount of discussion on adding the map_shadow_stack syscall instead of building 
new behaviors into mmap(). Ultimately, since there was no consensus and it was 
agreed that there wasn't impact on other archs, this was left as well.

Lastly, per Dave, the author for most of the the patches from the old series
has been swapped to me from Yu-cheng, so potential bisecters can find help
better. Previously these patches had me just as Co-developed-by.

At this point, I think we have a pretty good initial shadow stack implementation
here. I'd like to start with the basics and let real world usage inform the
enhancements if we can. Unless anyone sees any likely ABI trap we are walking
into.

I left tags in place.

Previous version [1].

Thanks,
Rick


[0] https://lore.kernel.org/lkml/[e-mail]/
[1] https://lore.kernel.org/lkml/[e-mail]/


Mike Rapoport (1):
  x86/shstk: Add ARCH_SHSTK_UNLOCK

Rick Edgecombe (36):
  Documentation/x86: Add CET shadow stack description
  x86/shstk: Add Kconfig option for shadow stack
  x86/cpufeatures: Add CPU feature flags for shadow stacks
  x86/cpufeatures: Enable CET CR4 bit for shadow stack
  x86/fpu/xstate: Introduce CET MSR and XSAVES supervisor states
  x86/fpu: Add helper for modifying xstate
  x86/traps: Move control protection handler to separate file
  x86/shstk: Add user control-protection fault handler
  x86/mm: Remove _PAGE_DIRTY from kernel RO pages
  x86/mm: Move pmd_write(), pud_write() up in the file
  mm: Introduce pte_mkwrite_kernel()
  s390/mm: Introduce pmd_mkwrite_kernel()
  mm: Make pte_mkwrite() take a VMA
  x86/mm: Introduce _PAGE_SAVED_DIRTY
  x86/mm: Update ptep/pmdp_set_wrprotect() for _PAGE_SAVED_DIRTY
  x86/mm: Start actually marking _PAGE_SAVED_DIRTY
  x86/mm: Check shadow stack page fault errors
  x86/mm: Teach pte_mkwrite() about stack memory
  mm: Add guard pages around a shadow stack.
  mm/mmap: Add shadow stack pages to memory accounting
  mm: Don't allow write GUPs to shadow stack memory
  x86/mm: Introduce MAP_ABOVE4G
  mm: Warn on shadow stack memory in wrong vma
  x86/mm: Warn if create Write=0,Dirty=1 with raw prot
  x86: Introduce userspace API for shadow stack
  x86/shstk: Add user-mode shadow stack support
  x86/shstk: Handle thread shadow stack
  x86/shstk: Introduce routines modifying shstk
  x86/shstk: Handle signals for shadow stack
  x86/shstk: Introduce map_shadow_stack syscall
  x86/shstk: Support WRSS for userspace
  x86: Expose thread features in /proc/$PID/status
  x86/shstk: Wire in shadow stack interface
  selftests/x86: Add shadow stack test
  x86: Add PTRACE interface for shadow stack
  x86/shstk: Add ARCH_SHSTK_STATUS

Yu-cheng Yu (3):
  mm: Move VM_UFFD_MINOR_BIT from 37 to 38
  mm: Introduce VM_SHADOW_STACK for shadow stack memory
  mm: Re-introduce vm_flags to do_mmap()

 Documentation/filesystems/proc.rst            |   1 +
 Documentation/mm/arch_pgtable_helpers.rst     |   9 +-
 Documentation/x86/index.rst                   |   1 +
 Documentation/x86/shstk.rst                   | 179 +++++
 arch/alpha/include/asm/pgtable.h              |   6 +-
 arch/arc/include/asm/hugepage.h               |   2 +-
 arch/arc/include/asm/pgtable-bits-arcv2.h     |   7 +-
 arch/arm/include/asm/pgtable-3level.h         |   7 +-
 arch/arm/include/asm/pgtable.h                |   2 +-
 arch/arm/kernel/signal.c                      |   2 +-
 arch/arm64/include/asm/pgtable.h              |   9 +-
 arch/arm64/kernel/signal.c                    |   2 +-
 arch/arm64/kernel/signal32.c                  |   2 +-
 arch/arm64/mm/trans_pgd.c                     |   4 +-
 arch/csky/include/asm/pgtable.h               |   2 +-
 arch/hexagon/include/asm/pgtable.h            |   2 +-
 arch/ia64/include/asm/pgtable.h               |   2 +-
 arch/loongarch/include/asm/pgtable.h          |   4 +-
 arch/m68k/include/asm/mcf_pgtable.h           |   2 +-
 arch/m68k/include/asm/motorola_pgtable.h      |   6 +-
 arch/m68k/include/asm/sun3_pgtable.h          |   6 +-
 arch/microblaze/include/asm/pgtable.h         |   2 +-
 arch/mips/include/asm/pgtable.h               |   6 +-
 arch/nios2/include/asm/pgtable.h              |   2 +-
 arch/openrisc/include/asm/pgtable.h           |   2 +-
 arch/parisc/include/asm/pgtable.h             |   6 +-
 arch/powerpc/include/asm/book3s/32/pgtable.h  |   2 +-
 arch/powerpc/include/asm/book3s/64/pgtable.h  |   4 +-
 arch/powerpc/include/asm/nohash/32/pgtable.h  |   2 +-
 arch/powerpc/include/asm/nohash/32/pte-8xx.h  |   2 +-
 arch/powerpc/include/asm/nohash/64/pgtable.h  |   2 +-
 arch/riscv/include/asm/pgtable.h              |   6 +-
 arch/s390/include/asm/hugetlb.h               |   4 +-
 arch/s390/include/asm/pgtable.h               |  14 +-
 arch/s390/mm/pageattr.c                       |   4 +-
 arch/sh/include/asm/pgtable_32.h              |  10 +-
 arch/sparc/include/asm/pgtable_32.h           |   2 +-
 arch/sparc/include/asm/pgtable_64.h           |   6 +-
 arch/sparc/kernel/signal32.c                  |   2 +-
 arch/sparc/kernel/signal_64.c                 |   2 +-
 arch/um/include/asm/pgtable.h                 |   2 +-
 arch/x86/Kconfig                              |  24 +
 arch/x86/Kconfig.assembler                    |   5 +
 arch/x86/entry/syscalls/syscall_64.tbl        |   1 +
 arch/x86/include/asm/cpufeatures.h            |   2 +
 arch/x86/include/asm/disabled-features.h      |  16 +-
 arch/x86/include/asm/fpu/api.h                |   9 +
 arch/x86/include/asm/fpu/regset.h             |   7 +-
 arch/x86/include/asm/fpu/sched.h              |   3 +-
 arch/x86/include/asm/fpu/types.h              |  16 +-
 arch/x86/include/asm/fpu/xstate.h             |   6 +-
 arch/x86/include/asm/idtentry.h               |   2 +-
 arch/x86/include/asm/mmu_context.h            |   2 +
 arch/x86/include/asm/pgtable.h                | 322 +++++++-
 arch/x86/include/asm/pgtable_types.h          |  56 +-
 arch/x86/include/asm/processor.h              |   8 +
 arch/x86/include/asm/shstk.h                  |  38 +
 arch/x86/include/asm/special_insns.h          |  13 +
 arch/x86/include/asm/tlbflush.h               |   3 +-
 arch/x86/include/asm/trap_pf.h                |   2 +
 arch/x86/include/asm/traps.h                  |  12 +
 arch/x86/include/uapi/asm/mman.h              |   4 +
 arch/x86/include/uapi/asm/prctl.h             |  12 +
 arch/x86/kernel/Makefile                      |   4 +
 arch/x86/kernel/cet.c                         | 152 ++++
 arch/x86/kernel/cpu/common.c                  |  35 +-
 arch/x86/kernel/cpu/cpuid-deps.c              |   1 +
 arch/x86/kernel/cpu/proc.c                    |  23 +
 arch/x86/kernel/fpu/core.c                    |  54 +-
 arch/x86/kernel/fpu/regset.c                  |  78 ++
 arch/x86/kernel/fpu/xstate.c                  |  90 ++-
 arch/x86/kernel/idt.c                         |   2 +-
 arch/x86/kernel/process.c                     |  21 +-
 arch/x86/kernel/process_64.c                  |   9 +-
 arch/x86/kernel/ptrace.c                      |  12 +
 arch/x86/kernel/shstk.c                       | 499 +++++++++++++
 arch/x86/kernel/signal.c                      |   1 +
 arch/x86/kernel/signal_32.c                   |   2 +-
 arch/x86/kernel/signal_64.c                   |   8 +-
 arch/x86/kernel/sys_x86_64.c                  |   6 +-
 arch/x86/kernel/traps.c                       |  87 ---
 arch/x86/mm/fault.c                           |  22 +
 arch/x86/mm/pat/set_memory.c                  |   4 +-
 arch/x86/mm/pgtable.c                         |  38 +
 arch/x86/xen/enlighten_pv.c                   |   2 +-
 arch/x86/xen/mmu_pv.c                         |   2 +-
 arch/x86/xen/xen-asm.S                        |   2 +-
 arch/xtensa/include/asm/pgtable.h             |   2 +-
 fs/aio.c                                      |   2 +-
 fs/proc/array.c                               |   6 +
 fs/proc/task_mmu.c                            |   3 +
 include/asm-generic/hugetlb.h                 |   4 +-
 include/linux/mm.h                            |  65 +-
 include/linux/mman.h                          |   4 +
 include/linux/pgtable.h                       |  14 +
 include/linux/proc_fs.h                       |   2 +
 include/linux/syscalls.h                      |   1 +
 include/uapi/asm-generic/siginfo.h            |   3 +-
 include/uapi/asm-generic/unistd.h             |   2 +-
 include/uapi/linux/elf.h                      |   2 +
 ipc/shm.c                                     |   2 +-
 kernel/sys_ni.c                               |   1 +
 mm/debug_vm_pgtable.c                         |  16 +-
 mm/gup.c                                      |   2 +-
 mm/huge_memory.c                              |   7 +-
 mm/hugetlb.c                                  |   4 +-
 mm/internal.h                                 |   4 +-
 mm/memory.c                                   |   5 +-
 mm/migrate_device.c                           |   2 +-
 mm/mmap.c                                     |  10 +-
 mm/mprotect.c                                 |   2 +-
 mm/nommu.c                                    |   4 +-
 mm/userfaultfd.c                              |   2 +-
 mm/util.c                                     |   2 +-
 tools/testing/selftests/x86/Makefile          |   2 +-
 .../testing/selftests/x86/test_shadow_stack.c | 695 ++++++++++++++++++
 116 files changed, 2612 insertions(+), 314 deletions(-)
 create mode 100644 Documentation/x86/shstk.rst
 create mode 100644 arch/x86/include/asm/shstk.h
 create mode 100644 arch/x86/kernel/cet.c
 create mode 100644 arch/x86/kernel/shstk.c
 create mode 100644 tools/testing/selftests/x86/test_shadow_stack.c


base-commit: eeac8ede17557680855031c6f305ece2378af326

Comments

Borislav Petkov March 19, 2023, 2 p.m. UTC | #1

On Sat, Mar 18, 2023 at 05:14:55PM -0700, Rick Edgecombe wrote:
> At this point, I think we have a pretty good initial shadow stack implementation
> here. I'd like to start with the basics and let real world usage inform the
> enhancements if we can.

Yes, finally!

That was loooong in the making. Thanks for the persistence and
patience.

For the whole set:

Reviewed-by: Borislav Petkov (AMD) <[e-mail]>

> Unless anyone sees any likely ABI trap we are walking into.

Yeah, dhansen, let's queue this and run it on everything and as much as
possible before the MW comes so that we can have a chance to catch any
potential showstopper snafus we've missed.

Thx.