Re: [PATCH v4 00/17] Add support for Clang CFI

From: Kees Cook
Date: Wed Mar 31 2021 - 17:46:54 EST

On Wed, Mar 31, 2021 at 02:27:04PM -0700, Sami Tolvanen wrote:
> This series adds support for Clang's Control-Flow Integrity (CFI)
> checking. 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 patch contains build system changes and error handling,
> and implements support for cross-module indirect call checking. The
> remaining patches address issues caused by the compiler
> instrumentation. These include fixing known type mismatches, as well
> as issues with address space confusion and cross-module function
> address equality.
>
> These patches add support only for arm64, but I'll post patches also
> for x86_64 after we address the remaining issues there, including
> objtool support.
>
> You can also pull this series from
>
> https://github.com/samitolvanen/linux.git cfi-v4

Thanks for the updates! I think this is ready to land in -next.

Will, Mark, Catalin: would you prefer this go via arm64 or via my LTO
tree? (Or does anyone see other stuff they'd like fixed first?)

-Kees

> ---
> Changes in v4:
> - Per Mark's suggestion, dropped __pa_function() and renamed
> __va_function() to function_nocfi().
> - Added a comment to function_nocfi() to explain what it does.
> - Updated the psci patch to use an intermediate variable for
> the physical address for clarity.
>
> Changes in v3:
> - Added a patch to change list_sort() callers treewide to use
> const pointers instead of simply removing the internal casts.
> - Changed cleanup_symbol_name() to return bool.
> - Changed module.lds.S to drop the .eh_frame section only with
> CONFIG_CFI_CLANG.
> - Switched to synchronize_rcu() in update_shadow().
>
> Changes in v2:
> - Fixed .text merging in module.lds.S.
> - Added WARN_ON_FUNCTION_MISMATCH() and changed kernel/thread.c
> and kernel/workqueue.c to use the macro instead.
>
>
> Sami Tolvanen (17):
> add support for Clang CFI
> cfi: add __cficanonical
> mm: add generic function_nocfi macro
> module: ensure __cfi_check alignment
> workqueue: use WARN_ON_FUNCTION_MISMATCH
> kthread: use WARN_ON_FUNCTION_MISMATCH
> kallsyms: strip ThinLTO hashes from static functions
> bpf: disable CFI in dispatcher functions
> treewide: Change list_sort to use const pointers
> lkdtm: use function_nocfi
> psci: use function_nocfi for cpu_resume
> arm64: implement function_nocfi
> arm64: use function_nocfi with __pa_symbol
> arm64: add __nocfi to functions that jump to a physical address
> arm64: add __nocfi to __apply_alternatives
> KVM: arm64: Disable CFI for nVHE
> arm64: allow CONFIG_CFI_CLANG to be selected
>
> Makefile | 17 +
> arch/Kconfig | 45 +++
> arch/arm64/Kconfig | 1 +
> arch/arm64/include/asm/memory.h | 15 +
> arch/arm64/include/asm/mmu_context.h | 4 +-
> arch/arm64/kernel/acpi_parking_protocol.c | 3 +-
> arch/arm64/kernel/alternative.c | 4 +-
> arch/arm64/kernel/cpu-reset.h | 10 +-
> arch/arm64/kernel/cpufeature.c | 4 +-
> arch/arm64/kernel/psci.c | 3 +-
> arch/arm64/kernel/smp_spin_table.c | 3 +-
> arch/arm64/kvm/hyp/nvhe/Makefile | 6 +-
> arch/arm64/kvm/vgic/vgic-its.c | 8 +-
> arch/arm64/kvm/vgic/vgic.c | 3 +-
> block/blk-mq-sched.c | 3 +-
> block/blk-mq.c | 3 +-
> drivers/acpi/nfit/core.c | 3 +-
> drivers/acpi/numa/hmat.c | 3 +-
> drivers/clk/keystone/sci-clk.c | 4 +-
> drivers/firmware/psci/psci.c | 7 +-
> drivers/gpu/drm/drm_modes.c | 3 +-
> drivers/gpu/drm/i915/gt/intel_engine_user.c | 3 +-
> drivers/gpu/drm/i915/gvt/debugfs.c | 2 +-
> drivers/gpu/drm/i915/selftests/i915_gem_gtt.c | 3 +-
> drivers/gpu/drm/radeon/radeon_cs.c | 4 +-
> .../hw/usnic/usnic_uiom_interval_tree.c | 3 +-
> drivers/interconnect/qcom/bcm-voter.c | 2 +-
> drivers/md/raid5.c | 3 +-
> drivers/misc/lkdtm/usercopy.c | 2 +-
> drivers/misc/sram.c | 4 +-
> drivers/nvme/host/core.c | 3 +-
> .../controller/cadence/pcie-cadence-host.c | 3 +-
> drivers/spi/spi-loopback-test.c | 3 +-
> fs/btrfs/raid56.c | 3 +-
> fs/btrfs/tree-log.c | 3 +-
> fs/btrfs/volumes.c | 3 +-
> fs/ext4/fsmap.c | 4 +-
> fs/gfs2/glock.c | 3 +-
> fs/gfs2/log.c | 2 +-
> fs/gfs2/lops.c | 3 +-
> fs/iomap/buffered-io.c | 3 +-
> fs/ubifs/gc.c | 7 +-
> fs/ubifs/replay.c | 4 +-
> fs/xfs/scrub/bitmap.c | 4 +-
> fs/xfs/xfs_bmap_item.c | 4 +-
> fs/xfs/xfs_buf.c | 6 +-
> fs/xfs/xfs_extent_busy.c | 4 +-
> fs/xfs/xfs_extent_busy.h | 3 +-
> fs/xfs/xfs_extfree_item.c | 4 +-
> fs/xfs/xfs_refcount_item.c | 4 +-
> fs/xfs/xfs_rmap_item.c | 4 +-
> include/asm-generic/bug.h | 16 +
> include/asm-generic/vmlinux.lds.h | 20 +-
> include/linux/bpf.h | 4 +-
> include/linux/cfi.h | 41 +++
> include/linux/compiler-clang.h | 3 +
> include/linux/compiler_types.h | 8 +
> include/linux/init.h | 6 +-
> include/linux/list_sort.h | 7 +-
> include/linux/mm.h | 10 +
> include/linux/module.h | 13 +-
> include/linux/pci.h | 4 +-
> init/Kconfig | 2 +-
> kernel/Makefile | 4 +
> kernel/cfi.c | 329 ++++++++++++++++++
> kernel/kallsyms.c | 55 ++-
> kernel/kthread.c | 3 +-
> kernel/module.c | 43 +++
> kernel/workqueue.c | 2 +-
> lib/list_sort.c | 17 +-
> lib/test_list_sort.c | 3 +-
> net/tipc/name_table.c | 4 +-
> scripts/Makefile.modfinal | 2 +-
> scripts/module.lds.S | 20 +-
> 74 files changed, 759 insertions(+), 112 deletions(-)
> create mode 100644 include/linux/cfi.h
> create mode 100644 kernel/cfi.c
>
>
> base-commit: d19cc4bfbff1ae72c3505a00fb8ce0d3fa519e6c
> --
> 2.31.0.291.g576ba9dcdaf-goog
>

--
Kees Cook