On Mon, 27 Jun 2016 10:06:57 -0400
David Long [off-list ref] wrote:

On 06/27/2016 02:57 AM, Pratyush Anand wrote:

quoted

Hi David,

On 26/06/2016:11:06:47 PM, David Long wrote:

quoted

From: Sandeepa Prabhu <redacted>

Add support for basic kernel probes(kprobes) and jump probes
(jprobes) for ARM64.

Kprobes utilizes software breakpoint and single step debug
exceptions supported on ARM v8.

A software breakpoint is placed at the probe address to trap the
kernel execution into the kprobe handler.

ARM v8 supports enabling single stepping before the break exception
return (ERET), with next PC in exception return address (ELR_EL1). The
kprobe handler prepares an executable memory slot for out-of-line
execution with a copy of the original instruction being probed, and
enables single stepping. The PC is set to the out-of-line slot address
before the ERET. With this scheme, the instruction is executed with the
exact same register context except for the PC (and DAIF) registers.

Debug mask (PSTATE.D) is enabled only when single stepping a recursive
kprobe, e.g.: during kprobes reenter so that probed instruction can be
single stepped within the kprobe handler -exception- context.
The recursion depth of kprobe is always 2, i.e. upon probe re-entry,
any further re-entry is prevented by not calling handlers and the case
counted as a missed kprobe).

Single stepping from the x-o-l slot has a drawback for PC-relative accesses
like branching and symbolic literals access as the offset from the new PC
(slot address) may not be ensured to fit in the immediate value of
the opcode. Such instructions need simulation, so reject
probing them.

Instructions generating exceptions or cpu mode change are rejected
for probing.

Exclusive load/store instructions are rejected too.  Additionally, the
code is checked to see if it is inside an exclusive load/store sequence
(code from Pratyush).

System instructions are mostly enabled for stepping, except MSR/MRS
accesses to "DAIF" flags in PSTATE, which are not safe for
probing.

Thanks to Steve Capper and Pratyush Anand for several suggested
Changes.

Signed-off-by: Sandeepa Prabhu <redacted>
Signed-off-by: David A. Long <redacted>
Signed-off-by: Pratyush Anand <redacted>
---
  arch/arm64/Kconfig                      |   1 +
  arch/arm64/include/asm/debug-monitors.h |   5 +
  arch/arm64/include/asm/insn.h           |   2 +
  arch/arm64/include/asm/kprobes.h        |  60 ++++
  arch/arm64/include/asm/probes.h         |  34 +++
  arch/arm64/include/asm/ptrace.h         |   1 +
  arch/arm64/kernel/Makefile              |   2 +-
  arch/arm64/kernel/debug-monitors.c      |  16 +-
  arch/arm64/kernel/kprobes/Makefile      |   1 +
  arch/arm64/kernel/kprobes/decode-insn.c | 143 +++++++++
  arch/arm64/kernel/kprobes/decode-insn.h |  34 +++
  arch/arm64/kernel/kprobes/kprobes.c     | 525 ++++++++++++++++++++++++++++++++
  arch/arm64/kernel/vmlinux.lds.S         |   1 +
  arch/arm64/mm/fault.c                   |  26 ++
  14 files changed, 848 insertions(+), 3 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/Makefile
  create mode 100644 arch/arm64/kernel/kprobes/decode-insn.c
  create mode 100644 arch/arm64/kernel/kprobes/decode-insn.h

Can we rename kernel/kprobes as kernel/probes? uprobes code will use
decode-insn.c and further simulate-insn.c as well. So, I would like to place my
uprobes.c in same directory.

I had some reservations about making it a "kprobes" subdir for that 
reason but the advice I got was to simply go with Masami Hiramatsu's 
specific feedback and have a subsequent uprobes patch move these files 
to a replacement "probes" subdir.  If there ends up being yet another 
revision of this patch maybe he will consider allowing it to be called 
"probes" from the start.

Yeah, if you've already been sure it will be done,
I'm OK to rename it "probe" :) I just didn't know your work.

quoted

quoted

  create mode 100644 arch/arm64/kernel/kprobes/kprobes.c

[...]

quoted

diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
index 6c0c7d3..c7bbeed 100644
--- a/arch/arm64/include/asm/ptrace.h
+++ b/arch/arm64/include/asm/ptrace.h

@@ -209,6 +209,7 @@ struct task_struct;
  int valid_user_regs(struct user_pt_regs *regs, struct task_struct *task);

  #define instruction_pointer(regs)	((unsigned long)(regs)->pc)
+#define instruction_pointer_set(regs, value)	((regs)->pc = ((u64) (value)))

IIRC, Will Daecon had asked to include asm-generic/ptrace.h into asm/ptrace.h when
I had done similar changes for uprobe needs. May be you can pick patch from
my uprobe tree.

Ah, right. we have something similar routines in asm-generic/ptrace.h.

Feel free to include it.

Thanks,

quoted

https://github.com/pratyushanand/linux/commit/bb3e114797c2888ed8ad528cca20e569dd2d818e

I will look at this.

quoted

~Pratyush

Thanks,
-dl

-- 
Masami Hiramatsu [off-list ref]