[PATCH v10 0/9] arm64: Add kernel probes (kprobes) support

From: David Long
Date: Mon Feb 29 2016 - 21:59:42 EST

From: "David A. Long" <dave.long@xxxxxxxxxx>

This patchset is heavily based on Sandeepa Prabhu's ARM v8 kprobes patches,
first seen in October 2013. This version attempts to address concerns raised by
reviewers and also fixes problems discovered during testing.

This patchset adds support for kernel probes(kprobes), jump probes(jprobes)
and return probes(kretprobes) support for ARM64.

The kprobes mechanism makes use of software breakpoint and single stepping
support available in the ARM v8 kernel.

Changes since v2 include:

1) Removal of NOP padding in kprobe XOL slots. Slots are now exactly one
instruction long.
2) Disabling of interrupts during execution in single-step mode.
3) Fixing of numerous problems in instruction simulation code (mostly
thanks to Will Cohen).
4) Support for the HAVE_REGS_AND_STACK_ACCESS_API feature is added, to allow
access to kprobes through debugfs.
5) kprobes is *not* enabled in defconfig.
6) Numerous complaints from checkpatch have been cleaned up, although a couple
remain as removing the function pointer typedefs results in ugly code.

Changes since v3 include:

1) Remove table-driven instruction parsing and replace with an if statement
calling out to old and new instruction test functions in insn.c.
2) I removed the addition of orig_x0 to ptrace.h.
3) Reorder the patches.
4) Replace the previous interrupt disabling (from Will Cohen) with
an improved solution (from Steve Capper).

Changes since v4 include:

1) Added insn.c functions to detect exception instructions and DAIF
read/write instructions, and use them to reject probing same.
2) Changed adr detect function to also recognize adrp. Reject both.
3) Added missing __kprobes for some new functions.
4) Added call to kprobes_fault_handler from mm do_page_fault.
5) Reject all non-simulated branch/ret instructions, not just those
that use an immediate offset.
6) Moved software breakpoint definitions into debug-monitors.h.
7) Removed "!XIP_KERNEL" from Kconfig.
8) changed kprobes_condition_check_t and kprobes_prepare_t to probes_*,
for future sharing with uprobes.
9) Removed bogus call to kprobes_restore_local_irqflag() from

Changes since v5 include:

1) Replaced installation of breakpoint hook with direct call from the
handlers in debug-monitors.c, as requested.
2) Reject probing of instructions that read the interrupt mask, in
addition to instructions that set it.
3) Cleaned up comments describing usage of Debug Mask.
4) Added KPROBE_REENTER case in reenter_kprobe.
5) Corrected the ifdef'd definitions for notify_page_fault() to be
consistent when KPROBES is not configed.
6) Changed "cpsr" to "pstate" for HAVE_REGS_AND_STACK_ACCESS_API feature.
7) Added back in missing new files in previous patch.
8) Changed two instances of pr_warning() to pr_warn().

Note that there seems to be at least a potential issue with kprobes
on multiple (possibly all) platforms having to do with use of kfree
inside of the kretprobes trampoline handler. This has manifested
occasionally in systemtap testing on arm64. There does not appear to
be an simple solution to the problem.

Changes since v6 include:

1) New trampoline code from Will Cohen fixes the occasional failure seen
when processing kretprobes by replacing the software breakpoint with
assembly code to implement the return to the original execution stream.
2) Changed ip0, ip1, fp, and lr to plain numbered registers for purposes
of recognizing them as an ascii string in the stack/reg access code.
3) Removed orig_x0.
4) Moved ARM_x* defines from arch/arm64/include/uapi/asm/ptrace.h to

Changes since v7 include:

1) Move trampoline entry/return code into separate ".S" file instead
of making it a macro in a header file.
2) Add missing register name definitions in asm-offsets.c and use them
in place of hard-coded integer offsets in the trampoline code.
3) Correct the values used to decode MSR immediate instructions, in insn.h.
4) Remove the currently unused simulate_none() function.

Changes since v8 include:

1) Replaced use of REG_OFFSET_NAME with GPR_OFFSET_NAME for numbered
2) Added an alias for "lr" in the register name lookup table, which perf
tools need to be able to recognize.
3) Changed the code for checking instruction types for probeability and
steppability as per review feedback.
4) Fixed the size of cache being flushed when filling single-step slot.
5) Fixed big-endian issues.
6) Blacklisted copy_to/from_user to avoid aborts while single-stepping.
7) Record conditional instructions that fail the conditional test just
like any other probed (non-conditional) instruction.
8) Removed use of magic number for detecting jprobe return and just
check the breakpoint address instead.
9) Got rid of the unnecessary arch/arm64/kprobes.h.
10) The PSTATE and SP are now properly saved in the kretprobe trampoline
11) This patch no longer depends on the "Consolidate redundant
register/stack access code" patch set.
12) Remove call to fixup_exception from kprobe_fault_handler.

Changes since v9 include:

1) Remove arch/arm/opcodes.c from the arm64 build and move the renamed
arm64_check_condition() function to armv8_deprecated.c. Remove the
2) Various other type and style changes suggested by Marc Zyngier.
3) Put back the call to fixup_exception from kprobe_fault_handler.
It proved to be necessary for correct operation.

David A. Long (4):
arm64: Add more test functions to insn.c
arm64: add copy_to/from_user to kprobes blacklist
arm64: add conditional instruction simulation support

Sandeepa Prabhu (4):
arm64: Kprobes with single stepping support
arm64: kprobes instruction simulation support
arm64: Add kernel return probes support (kretprobes)
kprobes: Add arm64 case in kprobe example module

William Cohen (1):
arm64: Add trampoline code for kretprobes

arch/arm64/Kconfig | 3 +
arch/arm64/include/asm/debug-monitors.h | 5 +
arch/arm64/include/asm/insn.h | 41 ++
arch/arm64/include/asm/kprobes.h | 62 ++++
arch/arm64/include/asm/probes.h | 45 +++
arch/arm64/include/asm/ptrace.h | 33 +-
arch/arm64/kernel/Makefile | 6 +-
arch/arm64/kernel/armv8_deprecated.c | 19 +-
arch/arm64/kernel/asm-offsets.c | 22 ++
arch/arm64/kernel/debug-monitors.c | 18 +-
arch/arm64/kernel/insn.c | 131 +++++++
arch/arm64/kernel/kprobes-arm64.c | 150 ++++++++
arch/arm64/kernel/kprobes-arm64.h | 35 ++
arch/arm64/kernel/kprobes.c | 616 +++++++++++++++++++++++++++++++
arch/arm64/kernel/kprobes_trampoline.S | 67 ++++
arch/arm64/kernel/probes-simulate-insn.c | 187 ++++++++++
arch/arm64/kernel/probes-simulate-insn.h | 28 ++
arch/arm64/kernel/ptrace.c | 117 ++++++
arch/arm64/kernel/vmlinux.lds.S | 1 +
arch/arm64/lib/copy_from_user.S | 1 +
arch/arm64/lib/copy_to_user.S | 1 +
arch/arm64/mm/fault.c | 25 ++
samples/kprobes/kprobe_example.c | 8 +
23 files changed, 1613 insertions(+), 8 deletions(-)
create mode 100644 arch/arm64/include/asm/kprobes.h
create mode 100644 arch/arm64/include/asm/probes.h
create mode 100644 arch/arm64/kernel/kprobes-arm64.c
create mode 100644 arch/arm64/kernel/kprobes-arm64.h
create mode 100644 arch/arm64/kernel/kprobes.c
create mode 100644 arch/arm64/kernel/kprobes_trampoline.S
create mode 100644 arch/arm64/kernel/probes-simulate-insn.c
create mode 100644 arch/arm64/kernel/probes-simulate-insn.h