[PATCH v13 00/12] tracing: wprobe: x86: Add wprobe for watchpoint

["Masami Hiramatsu (Google)" <mhiramat@kernel.org>]

Hi,

Here is the 13th version of the series for adding new wprobe (watch probe)
which provides memory access tracing event. Moreover, this can be used
via event trigger. Thus it can trace memory access on dynamically
allocated objects too.
The previous version is here:

  https://lore.kernel.org/all/178611679753.237811.10190793347982785419.stgit@devnote2/

This version adds RCU protection for kprobe_blacklist, fixes trigger
reference counting and error paths, eliminates race conditions in selftests,
and addresses review comments. See below for more details.

Changes in v13:
 - kprobes: Protect kprobe_blacklist with RCU to allow safe lockless
   traversals from atomic/NMI sections.
 - tracing/wprobe: Use %pS to format symbol and offset in trace_wprobe_show().
 - tracing/wprobe: Align WPROBE_DEFAULT_CLEAR_ADDRESS to 8 bytes using a
   dedicated u64 variable.
 - tracing/wprobe: Remove manual trigger count decrement to rely on core
   event_trigger_count().
 - tracing/wprobe: Check for field tokens before field parsing in clear_wprobe
   to avoid spurious error logs on numeric counts and avoid masking syntax
   errors.
 - tracing/wprobe: Fix trigger reference count leak and error cleanup paths
   in wprobe_trigger_cmd_parse().
 - x86/hw_breakpoints: Add compiler barrier() before checking cpu_dr7_seq.
 - HWBP: Add comments to modify_local_hw_breakpoint_addr() clarifying
   the early bp->attr.bp_addr update behavior during the NMI race window.
 - selftests/ftrace: Look up target functions dynamically in
   trigger-wprobe-syntax-errors.tc.
 - selftests/ftrace: Disable set_wprobe trigger before verifying clear_wprobe
   in trigger-wprobe.tc to prevent sample_timer_cb race conditions.
 - Documentation/trace: Add [:COUNT] to trigger syntax synopsis.

Public branch
-------------
I will push this branch as topic/wprobe-v2 to my tree so that it
can be easily tested.

https://git.kernel.org/pub/scm/linux/kernel/git/mhiramat/linux.git/log/?h=topic/wprobe-v2

This is based on linux-trace tree's linux-trace/for-next.

Usage
-----

The basic usage of this wprobe is similar to other probes;

  w:[GRP/][EVENT] [r|w|rw]@<ADDRESS|SYMBOL[+|-OFFS]>[:LEN] [FETCHARGS]

This defines a new wprobe event. For example, to trace jiffies update,
you can do;

 echo 'w:my_jiffies w@jiffies:8 value=+0($addr)' >> dynamic_events
 echo 1 > events/wprobes/my_jiffies/enable

Moreover, this can be combined with event trigger to trace the memory
access on slab objects. The trigger syntax is;

  set_wprobe:WPROBE_EVENT:FIELD[+|-OFFSET][:COUNT] [if FILTER]
  clear_wprobe:WPROBE_EVENT[:FIELD[+|-OFFSET][:COUNT]] [if FILTER]

set_wprobe sets WPROBE_EVENT's watch address on FIELD[+|-OFFSET].
clear_wprobe clears WPROBE_EVENT's watch address if it is set to
FIELD[+|-OFFSET]. If FIELD is omitted, forcibly clear the watch address
when trigger event is hit.

For example, trace the first 8 byte of the dentry data structure passed
to do_truncate() until it is deleted by dentry_kill().
(Note: all tracefs setup uses '>>' so that it does not kick do_truncate())

  # echo 'w:watch rw@0:8 address=$addr value=+0($addr)' > dynamic_events

  # echo 'f:truncate do_truncate dentry=$arg2' >> dynamic_events
  # echo 'set_wprobe:watch:dentry' >> events/fprobes/truncate/trigger

  # echo 'f:dentry_kill dentry_kill dentry=$arg1' >> dynamic_events
  # echo 'clear_wprobe:watch:dentry' >> events/fprobes/dentry_kill/trigger

  # echo 1 >> events/fprobes/truncate/enable
  # echo 1 >> events/fprobes/dentry_kill/enable

  # echo aaa > /tmp/hoge
  # echo bbb > /tmp/hoge
  # echo ccc > /tmp/hoge
  # rm /tmp/hoge

Then, the trace data will show;

 # tracer: nop
 #
 # entries-in-buffer/entries-written: 32/32   #P:8
 #
 #                                _-----=> irqs-off/BH-disabled
 #                               / _----=> need-resched
 #                              | / _---=> hardirq/softirq
 #                              || / _--=> preempt-depth
 #                              ||| / _-=> migrate-disable
 #                              |||| /     delay
 #           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
 #              | |         |   |||||     |         |
               sh-107     [004] ...1.     9.990418: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff888004ad6618
               sh-107     [004] ...1.     9.990914: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff888004b3de78
               sh-107     [004] ...1.     9.993175: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff8880049ddd40
               sh-107     [004] .....     9.995198: truncate: (do_truncate+0x4/0x120) dentry=0xffff8880048083a8
               sh-107     [004] ...1.     9.995389: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff8880049db998
               sh-107     [004] ..Zff     9.997503: watch: (lookup_fast+0xaa/0x150) address=0xffff8880048083a8 value=0x8200080
               sh-107     [004] ..Zff     9.997509: watch: (path_openat+0x211/0xda0) address=0xffff8880048083a8 value=0x8200080
               sh-107     [004] ..Zff     9.997514: watch: (path_openat+0xa56/0xda0) address=0xffff8880048083a8 value=0x8200080
               sh-107     [004] ..Zff     9.997518: watch: (path_openat+0xae2/0xda0) address=0xffff8880048083a8 value=0x8200080
               sh-107     [004] .....     9.997521: truncate: (do_truncate+0x4/0x120) dentry=0xffff8880048083a8
               sh-107     [004] ...1.     9.997582: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff888004808270
               sh-107     [004] ...1.     9.999365: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff8880049db728
               sh-107     [004] ...1.     9.999388: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff888004b1c000
               rm-113     [005] ..Zff    10.000965: watch: (lookup_fast+0xaa/0x150) address=0xffff8880048083a8 value=0x8200080
               rm-113     [005] ..Zff    10.000971: watch: (path_lookupat+0x97/0x1e0) address=0xffff8880048083a8 value=0x8200080
               rm-113     [005] ..Zff    10.000984: watch: (lookup_fast+0xaa/0x150) address=0xffff8880048083a8 value=0x8200080
               rm-113     [005] ..Zff    10.000988: watch: (path_lookupat+0x97/0x1e0) address=0xffff8880048083a8 value=0x8200080
               rm-113     [005] ..Zff    10.001010: watch: (lookup_one_qstr_excl+0x28/0x140) address=0xffff8880048083a8 value=0x8200080
               rm-113     [005] ..Zff    10.001014: watch: (lookup_one_qstr_excl+0xd1/0x140) address=0xffff8880048083a8 value=0x8200080
               rm-113     [005] ..Zff    10.001018: watch: (may_delete_dentry+0x1c/0x200) address=0xffff8880048083a8 value=0x8200080
               rm-113     [005] ..Zff    10.001021: watch: (may_delete_dentry+0x195/0x200) address=0xffff8880048083a8 value=0x8200080
               rm-113     [005] ..Zff    10.001031: watch: (vfs_unlink+0x5e/0x260) address=0xffff8880048083a8 value=0x8200080
               rm-113     [005] d.Z..    10.001067: watch: (d_make_discardable+0x1b/0x40) address=0xffff8880048083a8 value=0x8200080
               rm-113     [005] d.Z..    10.001071: watch: (d_make_discardable+0x29/0x40) address=0xffff8880048083a8 value=0x200080
               rm-113     [005] ...1.    10.001072: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff8880048083a8
               rm-113     [005] ...1.    10.001218: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff8880048083a8
               sh-107     [004] ...1.    10.001416: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff8880049db110
               sh-107     [004] ...1.    10.001444: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff8880049db248
               sh-107     [004] ...1.    10.001500: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff888004ad6618
               sh-107     [004] ...1.    10.002067: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff888004b41e78
               sh-107     [004] ...1.    10.904920: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff888004b41e78
               sh-107     [004] ...1.    10.905129: dentry_kill: (dentry_kill+0x0/0x2c0) dentry=0xffff888004ad6618


Thank you,

---
base-commit: 54f133c6178d06b169dceae18cc92c4945933b8c

Jinchao Wang (2):
      x86/hw_breakpoints: Make DR7 updates NMI safe
      x86/hw_breakpoints: Add arch_modify_local_hw_breakpoint_addr() API

Masami Hiramatsu (Google) (10):
      kprobes: Protect kprobe_blacklist with RCU
      HWBP: Add modify_local_hw_breakpoint_addr() API
      tracing/wprobe: Add wprobe (watchpoint probe) trace event support
      x86: hw_breakpoint: Add a kconfig to clarify when a breakpoint fires
      selftests: tracing: Add a basic testcase for wprobe
      selftests: tracing: Add syntax testcase for wprobe
      tracing/wprobe: Add set_wprobe and clear_wprobe event triggers
      selftests: ftrace: Add wprobe trigger testcase
      tracing/wprobe: Support BTF typecast in fetchargs
      tracing/wprobe: Support BTF struct offset resolution in set_wprobe trigger


 Documentation/trace/index.rst                      |    1 
 Documentation/trace/wprobetrace.rst                |  185 +++
 arch/Kconfig                                       |   18 
 arch/x86/Kconfig                                   |    2 
 arch/x86/include/asm/debugreg.h                    |   37 -
 arch/x86/include/asm/hw_breakpoint.h               |    2 
 arch/x86/kernel/cpu/mce/core.c                     |   20 
 arch/x86/kernel/hw_breakpoint.c                    |  139 +-
 arch/x86/kernel/nmi.c                              |    7 
 arch/x86/kernel/traps.c                            |   10 
 include/linux/hw_breakpoint.h                      |    6 
 include/linux/kprobes.h                            |    1 
 include/linux/trace_events.h                       |    3 
 kernel/events/hw_breakpoint.c                      |   48 +
 kernel/kprobes.c                                   |   14 
 kernel/trace/Kconfig                               |   24 
 kernel/trace/Makefile                              |    1 
 kernel/trace/trace.c                               |    9 
 kernel/trace/trace.h                               |    6 
 kernel/trace/trace_events_trigger.c                |    2 
 kernel/trace/trace_probe.c                         |   36 -
 kernel/trace/trace_probe.h                         |   22 
 kernel/trace/trace_wprobe.c                        | 1440 ++++++++++++++++++++
 tools/testing/selftests/ftrace/config              |    3 
 .../ftrace/test.d/dynevent/add_remove_wprobe.tc    |   63 +
 .../test.d/dynevent/wprobes_syntax_errors.tc       |   22 
 .../test.d/trigger/trigger-wprobe-btf-offset.tc    |   74 +
 .../test.d/trigger/trigger-wprobe-btf-typecast.tc  |   72 +
 .../test.d/trigger/trigger-wprobe-syntax-errors.tc |   37 +
 .../ftrace/test.d/trigger/trigger-wprobe.tc        |   87 +
 30 files changed, 2309 insertions(+), 82 deletions(-)
 create mode 100644 Documentation/trace/wprobetrace.rst
 create mode 100644 kernel/trace/trace_wprobe.c
 create mode 100644 tools/testing/selftests/ftrace/test.d/dynevent/add_remove_wprobe.tc
 create mode 100644 tools/testing/selftests/ftrace/test.d/dynevent/wprobes_syntax_errors.tc
 create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-wprobe-btf-offset.tc
 create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-wprobe-btf-typecast.tc
 create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-wprobe-syntax-errors.tc
 create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-wprobe.tc

--
Masami Hiramatsu (Google) <mhiramat@kernel.org>