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Subject[PATCH v15 00/10] arm64: Add kernel probes (kprobes) support
From: "David A. Long" <>

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

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.

Changes since v10 include:

1) Rename arm64_check_condition() to arm32_check_condition().
2) Remove redundant define of ARM_OPCODE_CONDITION_UNCOND.
3) Use a accessor functions to read and write registers by number
in the simulation code, to avoid accidentally overriding parts of
the pt_regs structure (e.g.: when the reg is xzr).
4) Remove unused register offset defines.
5) Replace instance of "(void *) 0" with NULL.
6) Rewrite the kretprobe trampoline code using arch/arm64/kvm/hyp/entry.S
as an example. Construct a more complete saved PSTATE in this code.

Changes since v11 include:

1) Add check for address within irq stack, in regs_within_kernel_stack()
2) Replaced inappropriate use of user_pt_regs with pt_regs.
3) Added comments to opcode_condition_checks table explaining equivalence
of "nv" and "al" condition codes.
4) Cleaned up some subtle problems in the instruction simulation code.
5) Readability improvements in kprobes_trampoline.S.
6) Additional blacklisting for entry code, exception handling code, and
select debug functions.
7) Check address to be probed for proper alignment.
8) Add rodata section to areas where kprobes may not be placed.

Changes since v12 include:

1) Changed regs_get_register() to expicitly reference pt_regs structure
fields instead of just using an address offset.
2) Reject probing of eret.
3) Correctly handle addresses on the interrupt stack
4) Add kprobe_ctlblk argument to static irqflag handling functions to avoid
doing extra calls to get_kprobe_ctlblk().
5) Removed a couple of logically redundant assignments to kprobe_status.
6) Added calls to pause_graph_tracing/unpause_graph_tracing to avoid
disaster when kprobe'ing and tracing at the same time.
7) Added idmap and hypervisor text sections to blacklisted regions
8) Numerous additional comments, formatting changes, and rearranging
of if-else statements.

Changes since v13 include:

1) Fixed regs_get_register() from previous version to correctly calculate
the offset of registers in struct pt_regs.
2) I removed the removal of the typecast inside the instruction_pointer()
define in ptrace.h, and added a define for instruction_pointer_set(). This
was necessary to correct warnings that were being emitted when compiling
kgdb code.
3) Removed a redundant/bogus "NOKPROBE_SYMBOL(do_debug_exception)"
4) Fixed aarch64_insn_extract_system_reg() from previous version to use the
correct name "aarch64_insn_extract_system_reg()".
5) Changed opcode_condition_checks[] to aarch32_opcode_cond_checks[] and
arm32_check_condition() to aarch32_check_condition().
6) I switched the order of the main kprobes patch and the symbol function
blacklisting patch back to the order they were done in the earlier patches.
7) I got rid of struct kprobe_pc_restore and now just use a non-zero saved
PC as the flag to restore the PC.
8) I changed the names of some of the arm64 kprobes source files and moved
then into their own "kprobes" subdirectory under arch/arm64/kernel.
9) I moved the INSN_GOOD_NO_SLOT enum value to the later commit that makes
use of it.
10) I added kernel_disable_single_stap() and spsr_set_debug_flag() calls in
kprobe_fault_handler() for the KPROBE_REENTER case.
11) I brought trampoline_probe_handler() up to date with x86 sources to
pick up a fix from Syuhei (commit 737480a0d525).
12) I changed samples/kprobes/kprobe_example.c modifications to more
closely match what is currently done for other architectures.

Changes since v14:

1) Change the name of arch/arm64/kernel/kprobes to
arch/arm64/kernel/probes/ and fix the name in the Makefile and comments.
2) Include include/linux/asm-generic/ptrace.h in
arch/arm64/include/asm/ptrace.h, add the required definitions in the latter
to make this work, and add a couple typecasts in
arch/arm64/kernel/probes/kprobes.c to accomodate this.
3) added Ack's to commits.

David A. Long (3):
arm64: Add more test functions to insn.c
arm64: add conditional instruction simulation support

Pratyush Anand (2):
arm64: Blacklist non-kprobe-able symbol
arm64: Treat all entry code as non-kprobe-able

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 | 35 ++
arch/arm64/include/asm/ptrace.h | 66 ++-
arch/arm64/kernel/Makefile | 5 +-
arch/arm64/kernel/arm64ksyms.c | 2 +
arch/arm64/kernel/armv8_deprecated.c | 19 +-
arch/arm64/kernel/asm-offsets.c | 11 +
arch/arm64/kernel/debug-monitors.c | 33 +-
arch/arm64/kernel/entry.S | 3 +
arch/arm64/kernel/hw_breakpoint.c | 8 +
arch/arm64/kernel/insn.c | 133 +++++
arch/arm64/kernel/kgdb.c | 4 +
arch/arm64/kernel/probes/Makefile | 3 +
arch/arm64/kernel/probes/decode-insn.c | 174 +++++++
arch/arm64/kernel/probes/decode-insn.h | 35 ++
arch/arm64/kernel/probes/kprobes.c | 675 ++++++++++++++++++++++++++
arch/arm64/kernel/probes/kprobes_trampoline.S | 85 ++++
arch/arm64/kernel/probes/simulate-insn.c | 218 +++++++++
arch/arm64/kernel/probes/simulate-insn.h | 28 ++
arch/arm64/kernel/ptrace.c | 118 +++++
arch/arm64/kernel/ | 2 +
arch/arm64/mm/fault.c | 26 +
samples/kprobes/kprobe_example.c | 9 +
26 files changed, 1794 insertions(+), 9 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/probes/Makefile
create mode 100644 arch/arm64/kernel/probes/decode-insn.c
create mode 100644 arch/arm64/kernel/probes/decode-insn.h
create mode 100644 arch/arm64/kernel/probes/kprobes.c
create mode 100644 arch/arm64/kernel/probes/kprobes_trampoline.S
create mode 100644 arch/arm64/kernel/probes/simulate-insn.c
create mode 100644 arch/arm64/kernel/probes/simulate-insn.h


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