[PATCH v3 00/12] arm64: ARMv8.5-A: Branch Target Identification support

From: Dave Martin
Date: Fri Oct 18 2019 - 13:26:21 EST


This patch 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.

The series is based on v5.4-rc2.

A branch for this series is available in Git [3].

This series supersedes the previous v2 posting [1], and also
incorporates my proposed ELF GNU property parsing implementation. (See
[2] for the ABI spec describing NT_GNU_PROPERTY_TYPE_0).

Changes:

* Minor cleanups / nitpick fixes only.

Since this is an interim update so that Mark Brown can take over
development of the series, I haven't fully retested. The series
builds with defconfig.

There are some outstanding discussion points: see notes in the
invidual patches, particularly on patch 5.


Notes:

* No documentation yet. We could do with some being written before
this series gets merged.

* 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.


[1] [PATCH v2 00/12] arm64: ARMv8.5-A: Branch Target Identification support
https://lore.kernel.org/lkml/1570733080-21015-1-git-send-email-Dave.Martin@xxxxxxx/

[2] Linux Extensions to gABI
https://github.com/hjl-tools/linux-abi/wiki/Linux-Extensions-to-gABI

[3] Git branch:
git://linux-arm.org/linux-dm.git arm64/bti/v3/head
http://linux-arm.org/git?p=linux-dm.git;a=shortlog;h=refs/heads/arm64/bti/v3/head


Dave Martin (12):
ELF: UAPI and Kconfig additions for ELF program properties
ELF: Add ELF program property parsing support
mm: Reserve asm-generic prot flag 0x10 for arch use
arm64: docs: cpu-feature-registers: Document ID_AA64PFR1_EL1
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: traps: Fix inconsistent faulting 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

Documentation/arm64/cpu-feature-registers.rst | 17 ++-
Documentation/arm64/elf_hwcaps.rst | 4 +
arch/arm64/Kconfig | 31 ++++++
arch/arm64/include/asm/cpucaps.h | 3 +-
arch/arm64/include/asm/cpufeature.h | 6 ++
arch/arm64/include/asm/elf.h | 50 +++++++++
arch/arm64/include/asm/esr.h | 2 +-
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 | 8 ++
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 | 1 +
arch/arm64/kernel/cpufeature.c | 33 ++++++
arch/arm64/kernel/cpuinfo.c | 1 +
arch/arm64/kernel/entry.S | 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 | 126 +++++++++++-----------
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/asm-generic/mman-common.h | 1 +
include/uapi/linux/elf.h | 11 ++
32 files changed, 560 insertions(+), 79 deletions(-)
create mode 100644 arch/arm64/include/asm/mman.h
create mode 100644 arch/arm64/include/uapi/asm/mman.h

--
2.1.4