The arm64 Guarded Control Stack (GCS) feature provides support for hardware protected stacks of return addresses, intended to provide hardening against return oriented programming (ROP) attacks and to make it easier to gather call stacks for applications such as profiling. When GCS is active a secondary stack called the Guarded Control Stack is maintained, protected with a memory attribute which means that it can only be written with specific GCS operations. When a BL is executed the value stored in LR is also pushed onto the GCS, and when a RET is executed the top of the GCS is popped and compared to LR with a fault being raised if the values do not match. GCS operations may only be performed on GCS pages, a data abort is generated if they are not. This series implements support for use of GCS by EL0, along with support for use of GCS within KVM guests. It does not enable use of GCS by either EL1 or EL2. Executables are started without GCS and must use a prctl() to enable it, it is expected that this will be done very early in application execution by the dynamic linker or other startup code. x86 has an equivalent feature called shadow stacks, this series depends on the x86 patches for generic memory management support for the new guarded/shadow stack page type and shares APIs as much as possible. As there has been extensive discussion with the wider community around the ABI for shadow stacks I have as far as practical kept implementation decisions close to those for x86, anticipating that review would lead to similar conclusions in the absence of strong reasoning for divergence. The main divergence I am concious of is that x86 allows shadow stack to be enabled and disabled repeatedly, freeing the shadow stack for the thread whenever disabled, while this implementation keeps the GCS allocated after disable but refuses to reenable it. This is to avoid races with things actively walking the GCS during a disable, we do anticipate that some systems will wish to disable GCS at runtime but are not aware of any demand for subsequently reenabling it. x86 uses an arch_prctl() to manage enable and disable, since only x86 and S/390 use arch_prctl() a generic prctl() was proposed[1] as part of a patch set for the equivalent RISC-V zisslpcfi feature which is adopted with some enhancements here. There's a few bits where I'm not convinced with where I've placed things, in particular the GCS write operation is in the GCS header not in uaccess.h, I wasn't sure what was clearest there and am probably too close to the code to have a clear opinion. The series depends on the x86 shadow stack support: https://lore.kernel.org/lkml/20230227222957.24501-1-rick.p.edgecombe@xxxxxxxxx/ I've rebased this onto v6.5-rc1 but not included it in the series in order to avoid confusion with Rick's work and cut down the size of the series, you can see the branch at: https://git.kernel.org/pub/scm/linux/kernel/git/broonie/misc.git arm64-gcs [1] https://lore.kernel.org/lkml/20230213045351.3945824-1-debug@xxxxxxxxxxxx/ Signed-off-by: Mark Brown <broonie@xxxxxxxxxx> --- Deepak Gupta (1): prctl: arch-agnostic prctl for shadow stack Mark Brown (34): prctl: Add flag for shadow stack writeability and push/pop arm64: Document boot requirements for Guarded Control Stacks arm64/gcs: Document the ABI for Guarded Control Stacks arm64/sysreg: Add new system registers for GCS arm64/sysreg: Add definitions for architected GCS caps arm64/gcs: Add manual encodings of GCS instructions arm64/gcs: Provide copy_to_user_gcs() arm64/cpufeature: Runtime detection of Guarded Control Stack (GCS) arm64/mm: Allocate PIE slots for EL0 guarded control stack mm: Define VM_SHADOW_STACK for arm64 when we support GCS arm64/mm: Map pages for guarded control stack KVM: arm64: Manage GCS registers for guests arm64: Disable traps for GCS usage at EL0 and EL1 arm64/idreg: Add overrride for GCS arm64/hwcap: Add hwcap for GCS arm64/traps: Handle GCS exceptions arm64/mm: Handle GCS data aborts arm64/gcs: Context switch GCS registers for EL0 arm64/gcs: Allocate a new GCS for threads with GCS enabled arm64/gcs: Implement shadow stack prctl() interface arm64/mm: Implement map_shadow_stack() arm64/signal: Set up and restore the GCS context for signal handlers arm64/signal: Expose GCS state in signal frames arm64/ptrace: Expose GCS via ptrace and core files arm64: Add Kconfig for Guarded Control Stack (GCS) kselftest/arm64: Verify the GCS hwcap kselftest/arm64: Add GCS as a detected feature in the signal tests kselftest/arm64: Add framework support for GCS to signal handling tests kselftest/arm64: Allow signals tests to specify an expected si_code kselftest/arm64: Always run signals tests with GCS enabled kselftest/arm64: Add very basic GCS test program kselftest/arm64: Add a GCS test program built with the system libc selftests/arm64: Add GCS signal tests kselftest/arm64: Enable GCS for the FP stress tests Documentation/admin-guide/kernel-parameters.txt | 3 + Documentation/arch/arm64/booting.rst | 22 ++ Documentation/arch/arm64/elf_hwcaps.rst | 3 + Documentation/arch/arm64/gcs.rst | 216 +++++++++++++ Documentation/arch/arm64/index.rst | 1 + Documentation/filesystems/proc.rst | 2 +- arch/arm64/Kconfig | 19 ++ arch/arm64/include/asm/cpufeature.h | 6 + arch/arm64/include/asm/el2_setup.h | 9 + arch/arm64/include/asm/esr.h | 26 +- arch/arm64/include/asm/exception.h | 2 + arch/arm64/include/asm/gcs.h | 88 ++++++ arch/arm64/include/asm/hwcap.h | 1 + arch/arm64/include/asm/kvm_host.h | 12 + arch/arm64/include/asm/pgtable-prot.h | 14 +- arch/arm64/include/asm/processor.h | 6 + arch/arm64/include/asm/sysreg.h | 20 ++ arch/arm64/include/asm/uaccess.h | 42 +++ arch/arm64/include/uapi/asm/hwcap.h | 1 + arch/arm64/include/uapi/asm/ptrace.h | 7 + arch/arm64/include/uapi/asm/sigcontext.h | 9 + arch/arm64/kernel/cpufeature.c | 23 ++ arch/arm64/kernel/cpuinfo.c | 1 + arch/arm64/kernel/entry-common.c | 23 ++ arch/arm64/kernel/idreg-override.c | 2 + arch/arm64/kernel/process.c | 77 +++++ arch/arm64/kernel/ptrace.c | 50 +++ arch/arm64/kernel/signal.c | 240 +++++++++++++- arch/arm64/kernel/traps.c | 11 + arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h | 17 + arch/arm64/kvm/sys_regs.c | 22 ++ arch/arm64/mm/Makefile | 1 + arch/arm64/mm/fault.c | 75 ++++- arch/arm64/mm/gcs.c | 202 ++++++++++++ arch/arm64/mm/mmap.c | 17 +- arch/arm64/tools/cpucaps | 1 + arch/arm64/tools/sysreg | 55 ++++ fs/proc/task_mmu.c | 3 + include/linux/mm.h | 15 +- include/linux/syscalls.h | 1 + include/uapi/asm-generic/unistd.h | 5 +- include/uapi/linux/elf.h | 1 + include/uapi/linux/prctl.h | 19 ++ kernel/sys.c | 20 ++ kernel/sys_ni.c | 1 + tools/testing/selftests/arm64/Makefile | 2 +- tools/testing/selftests/arm64/abi/hwcap.c | 19 ++ tools/testing/selftests/arm64/fp/assembler.h | 15 + tools/testing/selftests/arm64/fp/fpsimd-test.S | 2 + tools/testing/selftests/arm64/fp/sve-test.S | 2 + tools/testing/selftests/arm64/fp/za-test.S | 2 + tools/testing/selftests/arm64/fp/zt-test.S | 2 + tools/testing/selftests/arm64/gcs/.gitignore | 2 + tools/testing/selftests/arm64/gcs/Makefile | 19 ++ tools/testing/selftests/arm64/gcs/basic-gcs.c | 350 +++++++++++++++++++++ tools/testing/selftests/arm64/gcs/gcs-util.h | 65 ++++ tools/testing/selftests/arm64/gcs/libc-gcs.c | 217 +++++++++++++ tools/testing/selftests/arm64/signal/.gitignore | 1 + .../testing/selftests/arm64/signal/test_signals.c | 17 +- .../testing/selftests/arm64/signal/test_signals.h | 6 + .../selftests/arm64/signal/test_signals_utils.c | 32 +- .../selftests/arm64/signal/test_signals_utils.h | 39 +++ .../arm64/signal/testcases/gcs_exception_fault.c | 59 ++++ .../selftests/arm64/signal/testcases/gcs_frame.c | 78 +++++ .../arm64/signal/testcases/gcs_write_fault.c | 67 ++++ .../selftests/arm64/signal/testcases/testcases.c | 7 + .../selftests/arm64/signal/testcases/testcases.h | 1 + 67 files changed, 2363 insertions(+), 32 deletions(-) --- base-commit: 023ee2d672f3d7c2d15acf62bcfc4bc49c3677e5 change-id: 20230303-arm64-gcs-e311ab0d8729 Best regards, -- Mark Brown <broonie@xxxxxxxxxx>
