[PATCH v7 00/11] arm64: Branch Target Identification support

Mark Brown
2020-02-26T15:57:22Z

This patch series implements support for ARMv8.5-A Branch Target
Identification (BTI), which is a control flow integrity protection
feature introduced as part of the ARMv8.5-A extensions.

Changes:

v7:
- Rebase onto v5.6-rc3.
- Move comment about keeping NT_GNU_PROPERTY_TYPE_0 internal into first
patch.
- Add an explicit check for system_supports_bti() when parsing BTI ELF
property for improved robustness.
v6:
- Rebase onto v5.6-rc1.
- Fix typos s/BYTPE/BTYPE/ in commit log for "arm64: BTI: Decode BYTPE
bits when printing PSTATE".
v5:
- Changed a bunch of -EIO to -ENOEXEC in the ELF parsing code.
- Move PSR_BTYPE defines to UAPI.
- Use compat_user_mode() rather than open coding.
- Fix a typo s/BYTPE/BTYPE/ in syscall.c
v4:
- Dropped patch fixing existing documentation as it has already been merged.
- Convert WARN_ON() to WARN_ON_ONCE() in "ELF: Add ELF program property
parsing support".
- Added display of guarded pages to ptdump.
- Updated for conversion of exception handling from assembler to C.

Notes:

* GCC 9 can compile backwards-compatible BTI-enabled code with
-mbranch-protection=bti or -mbranch-protection=standard.

* Binutils trunk supports the new ELF note, but this wasn't in a release
the last time I posted this series. (The situation _might_ have changed
in the meantime...)

Creation of a BTI-enabled binary requires _everything_ linked in to
be BTI-enabled. For now ld --force-bti can be used to override this,
but some things may break until the required C library support is in
place.

There is no straightforward way to mark a .s file as BTI-enabled:
scraping the output from gcc -S works as a quick hack for now.

readelf -n can be used to examing the program properties in an ELF
file.

* Runtime mmap() and mprotect() can be used to enable BTI on a
page-by-page basis using the new PROT_BTI, but the code in the
affected pages still needs to be written or compiled to contain the
appopriate BTI landing pads.

The following changes since commit f8788d86ab28f61f7b46eb6be375f8a726783636:

Linux 5.6-rc3 (2020-02-23 16:17:42 -0800)

are available in the Git repository at:

https://git.kernel.org/pub/scm/linux/kernel/git/broonie/misc.git arm64-bti

for you to fetch changes up to d6897bb309fc4ef374e1de8242eb94d1fb97c13b:

arm64: mm: Display guarded pages in ptdump (2020-02-26 12:12:31 +0000)

Dave Martin (10):
ELF: UAPI and Kconfig additions for ELF program properties
ELF: Add ELF program property parsing support
arm64: Basic Branch Target Identification support
elf: Allow arch to tweak initial mmap prot flags
arm64: elf: Enable BTI at exec based on ELF program properties
arm64: BTI: Decode BYTPE bits when printing PSTATE
arm64: unify native/compat instruction skipping
arm64: traps: Shuffle code to eliminate forward declarations
arm64: BTI: Reset BTYPE when skipping emulated instructions
KVM: arm64: BTI: Reset BTYPE when skipping emulated instructions

Mark Brown (1):
arm64: mm: Display guarded pages in ptdump

Documentation/arm64/cpu-feature-registers.rst | 2 +
Documentation/arm64/elf_hwcaps.rst | 5 +
arch/arm64/Kconfig | 25 +++
arch/arm64/include/asm/cpucaps.h | 3 +-
arch/arm64/include/asm/cpufeature.h | 6 +
arch/arm64/include/asm/elf.h | 51 ++++++
arch/arm64/include/asm/esr.h | 2 +-
arch/arm64/include/asm/exception.h | 1 +
arch/arm64/include/asm/hwcap.h | 1 +
arch/arm64/include/asm/kvm_emulate.h | 6 +-
arch/arm64/include/asm/mman.h | 37 +++++
arch/arm64/include/asm/pgtable-hwdef.h | 1 +
arch/arm64/include/asm/pgtable.h | 2 +-
arch/arm64/include/asm/ptrace.h | 1 +
arch/arm64/include/asm/sysreg.h | 4 +
arch/arm64/include/uapi/asm/hwcap.h | 1 +
arch/arm64/include/uapi/asm/mman.h | 9 ++
arch/arm64/include/uapi/asm/ptrace.h | 9 ++
arch/arm64/kernel/cpufeature.c | 33 ++++
arch/arm64/kernel/cpuinfo.c | 1 +
arch/arm64/kernel/entry-common.c | 11 ++
arch/arm64/kernel/process.c | 36 ++++-
arch/arm64/kernel/ptrace.c | 2 +-
arch/arm64/kernel/signal.c | 16 ++
arch/arm64/kernel/syscall.c | 18 +++
arch/arm64/kernel/traps.c | 127 +++++++--------
arch/arm64/mm/dump.c | 5 +
fs/Kconfig.binfmt | 6 +
fs/binfmt_elf.c | 145 +++++++++++++++++-
fs/compat_binfmt_elf.c | 4 +
include/linux/elf.h | 43 ++++++
include/linux/mm.h | 3 +
include/uapi/linux/elf.h | 11 ++
33 files changed, 552 insertions(+), 75 deletions(-)
create mode 100644 arch/arm64/include/asm/mman.h
create mode 100644 arch/arm64/include/uapi/asm/mman.h

--
2.20.1