[PATCH 00/12] arm64/bti: Fix kernel BTI issues with livepatch, large kernels, toolchains

These patches are a continuation of the following discussions about some
bugs related to kernel BTI:

  https://lore.kernel.org/ed4fe1f95071897859ec7fbe9176246cbd4962bf.1786138806.git.jpoimboe@kernel.org (local)
  https://lore.kernel.org/20260812162058.612202-4-ardb@kernel.org (local)

This started as a livepatch crash investigation but quickly ballooned
into a rabbit hole of latent bugs and toolchain quirks/crashes.

The most notable patch is probably the last one, which enables BTI on GCC.

I also hit a SIGSEGV in the GNU linker, for which this series has a
workaround.  The binutils bug is here:

  https://sourceware.org/bugzilla/show_bug.cgi?id=34525

Several of these patches probably wouldn't be needed if we had a flag
like -fno-omit-bti-pads or so for both compilers, but that currently
doesn't exist, and this at least fixes things for the existing
toolchains out there.

There is some toolchain discussion about that here:

 https://github.com/llvm/llvm-project/issues/215547

Josh Poimboeuf (12):
  arm64/bti: Add BTI landing pad to __sdei_asm_handler()
  arm64/module: Fix BTI exceptions caused by omitted landing pads in
    Clang 21
  arm64/bti: Fix BTI linker failures with long branches into .idmap.text
  arm64/bti: Work around ld crash caused by linker script aliases
  arm64/bti: Add link error for large kernels with BTI and unsupported
    toolchains
  arm64/bti: Add link error for large kernels with BTI and livepatch
  arm64/bti: Advertise BTI in assembly objects
  arm64/bti: Enable BTI in the pi/ startup code
  efi/libstub: Preserve the GNU property note
  efi/libstub: Remove obsolete .note.gnu.property workaround
  arm64/bti: Force-enable BTI linker veneers
  arm64/bti: Enable kernel BTI for GCC

 arch/arm64/Kconfig                    |   9 +-
 arch/arm64/Makefile                   |   5 +
 arch/arm64/include/asm/bti-note.h     |  32 +++++
 arch/arm64/include/asm/module.h       |   5 +
 arch/arm64/kernel/cpu-reset.S         |   2 +-
 arch/arm64/kernel/entry.S             |   1 +
 arch/arm64/kernel/head.S              |   8 +-
 arch/arm64/kernel/hyp-stub.S          |   1 +
 arch/arm64/kernel/image-vars.h        |  13 +-
 arch/arm64/kernel/module-plts.c       | 186 ++++++++++++++++++++++++++
 arch/arm64/kernel/pi/Makefile         |  11 +-
 arch/arm64/kernel/sleep.S             |   2 +-
 arch/arm64/kernel/vmlinux.lds.S       |  12 ++
 arch/arm64/lib/memcpy.S               |   3 +
 arch/arm64/lib/memset.S               |   2 +
 arch/arm64/mm/cache.S                 |   1 +
 arch/arm64/mm/proc.S                  |   8 +-
 drivers/firmware/efi/libstub/Makefile |  15 ++-
 18 files changed, 282 insertions(+), 34 deletions(-)
 create mode 100644 arch/arm64/include/asm/bti-note.h

-- 
2.55.0