[PATCH v4 00/39] Shadow stacks for userspace

Rick Edgecombe
2022-12-03T00:36:31Z

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 permissioned 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].

I humbly think this is looking decent at this point, please consider applying.

Again there were some smaller changes (logged in the patches). The more
noteworthy changes were:
- Separate Shadow stack from IBT in kernel APIs. This involves renaming the
arch_prctl()s. And changing the ptrace cet regset interface to only expose
the SSP, and not any IBT bits.
- Handle 32 bit case more completely. (see commit log of “x86: Prevent 32 bit
operations for 64 bit shstk tasks” for the details)
- Drop elf header bit filtering compatibility patch for now, per Linus. [1]
- Break apart _PAGE_COW patch for bisectability reasons.

I left the Tested-by tags that were already in place, testers please re-test.

Previous version [2].

Thanks,

Rick

[0] https://lore.kernel.org/lkml/20220130211838.8382-1-rick.p.edgecombe@intel.com/
[1] https://lore.kernel.org/lkml/CAHk-=wgP5mk3poVeejw16Asbid0ghDt4okHnWaWKLBkRhQntRA@mail.gmail.com/
[2] https://lore.kernel.org/lkml/20221104223604.29615-1-rick.p.edgecombe@intel.com/

Kirill A. Shutemov (1):
x86: Introduce userspace API for shadow stack

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

Rick Edgecombe (13):
x86/fpu: Add helper for modifying xstate
x86/mm: Introduce _PAGE_COW
x86/mm: Start actually marking _PAGE_COW
mm: Don't allow write GUPs to shadow stack memory
mm: Warn on shadow stack memory in wrong vma
x86/shstk: Introduce map_shadow_stack syscall
x86/shstk: Support wrss for userspace
x86: Expose thread features in /proc/$PID/status
x86: Prevent 32 bit operations for 64 bit shstk tasks
x86/shstk: Wire in shadow stack interface
selftests/x86: Add shadow stack test
x86/fpu: Add helper for initing features
x86/shstk: Add ARCH_SHSTK_STATUS

Yu-cheng Yu (24):
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: 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
x86/mm: Update pte_modify for _PAGE_COW
x86/mm: Update ptep_set_wrprotect() and pmdp_set_wrprotect() for
transition from _PAGE_DIRTY to _PAGE_COW
mm: Move VM_UFFD_MINOR_BIT from 37 to 38
mm: Introduce VM_SHADOW_STACK for shadow stack memory
x86/mm: Check Shadow Stack page fault errors
x86/mm: Update maybe_mkwrite() for shadow stack
mm: Fixup places that call pte_mkwrite() directly
mm: Add guard pages around a shadow stack.
mm/mmap: Add shadow stack pages to memory accounting
mm/mprotect: Exclude shadow stack from preserve_write
mm: Re-introduce vm_flags to do_mmap()
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: Add PTRACE interface for shadow stack

Documentation/filesystems/proc.rst | 1 +
Documentation/x86/index.rst | 1 +
Documentation/x86/shstk.rst | 172 +++++
arch/arm/kernel/signal.c | 2 +-
arch/arm64/kernel/signal.c | 2 +-
arch/arm64/kernel/signal32.c | 2 +-
arch/sparc/kernel/signal32.c | 2 +-
arch/sparc/kernel/signal_64.c | 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 | 14 +-
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/msr.h | 11 +
arch/x86/include/asm/pgtable.h | 320 +++++++-
arch/x86/include/asm/pgtable_types.h | 65 +-
arch/x86/include/asm/processor.h | 8 +
arch/x86/include/asm/shstk.h | 52 ++
arch/x86/include/asm/sighandling.h | 1 +
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/uapi/asm/mman.h | 3 +
arch/x86/include/uapi/asm/prctl.h | 12 +
arch/x86/kernel/Makefile | 2 +
arch/x86/kernel/cpu/common.c | 37 +-
arch/x86/kernel/cpu/cpuid-deps.c | 1 +
arch/x86/kernel/cpu/proc.c | 23 +
arch/x86/kernel/fpu/core.c | 60 +-
arch/x86/kernel/fpu/regset.c | 87 +++
arch/x86/kernel/fpu/xstate.c | 148 ++--
arch/x86/kernel/fpu/xstate.h | 6 +
arch/x86/kernel/idt.c | 2 +-
arch/x86/kernel/process.c | 18 +-
arch/x86/kernel/process_64.c | 8 +
arch/x86/kernel/ptrace.c | 12 +
arch/x86/kernel/shstk.c | 495 +++++++++++++
arch/x86/kernel/signal.c | 21 +
arch/x86/kernel/signal_64.c | 6 +
arch/x86/kernel/signal_compat.c | 7 +-
arch/x86/kernel/traps.c | 107 ++-
arch/x86/mm/fault.c | 38 +
arch/x86/mm/pat/set_memory.c | 2 +-
arch/x86/mm/pgtable.c | 6 +
arch/x86/xen/enlighten_pv.c | 2 +-
arch/x86/xen/xen-asm.S | 2 +-
fs/aio.c | 2 +-
fs/proc/array.c | 6 +
fs/proc/task_mmu.c | 3 +
include/linux/mm.h | 57 +-
include/linux/pgtable.h | 35 +
include/linux/proc_fs.h | 2 +
include/linux/ptrace.h | 1 +
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/signal.c | 8 +
kernel/sys_ni.c | 1 +
mm/gup.c | 2 +-
mm/huge_memory.c | 20 +-
mm/memory.c | 7 +-
mm/migrate_device.c | 4 +-
mm/mmap.c | 12 +-
mm/mprotect.c | 8 +
mm/nommu.c | 4 +-
mm/userfaultfd.c | 10 +-
mm/util.c | 2 +-
tools/testing/selftests/x86/Makefile | 4 +-
.../testing/selftests/x86/test_shadow_stack.c | 685 ++++++++++++++++++
78 files changed, 2560 insertions(+), 178 deletions(-)
create mode 100644 Documentation/x86/shstk.rst
create mode 100644 arch/x86/include/asm/shstk.h
create mode 100644 arch/x86/kernel/shstk.c
create mode 100644 tools/testing/selftests/x86/test_shadow_stack.c

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2.17.1