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Subject[PATCH 2/7] ptrace: introduce ptrace_event_enabled() and simplify ptrace_event() and tracehook_prepare_clone()
Date
This patch implements ptrace_event_enabled() which tests whether a
given PTRACE_EVENT_* is enabled and use it to simplify ptrace_event()
and tracehook_prepare_clone().

PT_EVENT_FLAG() macro is added which calculates PT_TRACE_* flag from
PTRACE_EVENT_*. This is used to define PT_TRACE_* flags and by
ptrace_event_enabled() to find the matching flag.

This is used to make ptrace_event() and tracehook_prepare_clone()
simpler.

* ptrace_event() callers were responsible for providing mask to test
whether the event was enabled. This patch implements
ptrace_event_enabled() and make ptrace_event() drop @mask and
determine whether the event is enabled from @event. Note that
@event is constant and this conversion doesn't add runtime overhead.

All conversions except tracehook_report_clone_complete() are
trivial. tracehook_report_clone_complete() used to use 0 for @mask
(always enabled) but now tests whether the specified event is
enabled. This doesn't cause any behavior difference as it's
guaranteed that the event specified by @trace is enabled.

* tracehook_prepare_clone() now only determines which event is
applicable and use ptrace_event_enabled() for enable test.

This doesn't introduce any behavior change.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
include/linux/ptrace.h | 46 +++++++++++++++++++++++++++++++-------------
include/linux/tracehook.h | 26 ++++++++++++------------
2 files changed, 45 insertions(+), 27 deletions(-)

diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index 3ff20b3..18feac6 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -90,12 +90,17 @@
#define PT_DTRACE 0x00000002 /* delayed trace (used on m68k, i386) */
#define PT_TRACESYSGOOD 0x00000004
#define PT_PTRACE_CAP 0x00000008 /* ptracer can follow suid-exec */
-#define PT_TRACE_FORK 0x00000010
-#define PT_TRACE_VFORK 0x00000020
-#define PT_TRACE_CLONE 0x00000040
-#define PT_TRACE_EXEC 0x00000080
-#define PT_TRACE_VFORK_DONE 0x00000100
-#define PT_TRACE_EXIT 0x00000200
+
+/* PT_TRACE_* event enable flags */
+#define PT_EVENT_FLAG_SHIFT 4
+#define PT_EVENT_FLAG(event) (1 << (PT_EVENT_FLAG_SHIFT + (event) - 1))
+
+#define PT_TRACE_FORK PT_EVENT_FLAG(PTRACE_EVENT_FORK)
+#define PT_TRACE_VFORK PT_EVENT_FLAG(PTRACE_EVENT_VFORK)
+#define PT_TRACE_CLONE PT_EVENT_FLAG(PTRACE_EVENT_CLONE)
+#define PT_TRACE_EXEC PT_EVENT_FLAG(PTRACE_EVENT_EXEC)
+#define PT_TRACE_VFORK_DONE PT_EVENT_FLAG(PTRACE_EVENT_VFORK_DONE)
+#define PT_TRACE_EXIT PT_EVENT_FLAG(PTRACE_EVENT_EXIT)

#define PT_TRACE_MASK 0x000003f4

@@ -146,25 +151,38 @@ int generic_ptrace_pokedata(struct task_struct *tsk, unsigned long addr,
unsigned long data);

/**
+ * ptrace_event_enabled - test whether a ptrace event is enabled
+ * @task: ptracee of interest
+ * @event: %PTRACE_EVENT_* to test
+ *
+ * Test whether @event is enabled for ptracee @task.
+ *
+ * Returns %true if @event is enabled, %false otherwise.
+ */
+static inline bool ptrace_event_enabled(struct task_struct *task, int event)
+{
+ return task->ptrace & PT_EVENT_FLAG(event);
+}
+
+/**
* ptrace_event - possibly stop for a ptrace event notification
- * @mask: %PT_* bit to check in @current->ptrace
- * @event: %PTRACE_EVENT_* value to report if @mask is set
+ * @event: %PTRACE_EVENT_* value to report
* @message: value for %PTRACE_GETEVENTMSG to return
*
- * This checks the @mask bit to see if ptrace wants stops for this event.
- * If so we stop, reporting @event and @message to the ptrace parent.
+ * Check whether @event is enabled and, if so, report @event and @message
+ * to the ptrace parent.
*
* Returns nonzero if we did a ptrace notification, zero if not.
*
* Called without locks.
*/
-static inline int ptrace_event(int mask, int event, unsigned long message)
+static inline int ptrace_event(int event, unsigned long message)
{
- if (mask && likely(!(current->ptrace & mask)))
- return 0;
+ if (likely(!ptrace_event_enabled(current, event)))
+ return false;
current->ptrace_message = message;
ptrace_notify((event << 8) | SIGTRAP);
- return 1;
+ return true;
}

/**
diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
index a3e8387..7d38571 100644
--- a/include/linux/tracehook.h
+++ b/include/linux/tracehook.h
@@ -201,7 +201,7 @@ static inline void tracehook_report_exec(struct linux_binfmt *fmt,
struct linux_binprm *bprm,
struct pt_regs *regs)
{
- if (!ptrace_event(PT_TRACE_EXEC, PTRACE_EVENT_EXEC, 0) &&
+ if (!ptrace_event(PTRACE_EVENT_EXEC, 0) &&
unlikely(current->ptrace & PT_PTRACED))
send_sig(SIGTRAP, current, 0);
}
@@ -218,7 +218,7 @@ static inline void tracehook_report_exec(struct linux_binfmt *fmt,
*/
static inline void tracehook_report_exit(long *exit_code)
{
- ptrace_event(PT_TRACE_EXIT, PTRACE_EVENT_EXIT, *exit_code);
+ ptrace_event(PTRACE_EVENT_EXIT, *exit_code);
}

/**
@@ -232,19 +232,19 @@ static inline void tracehook_report_exit(long *exit_code)
*/
static inline int tracehook_prepare_clone(unsigned clone_flags)
{
+ int event = 0;
+
if (clone_flags & CLONE_UNTRACED)
return 0;

- if (clone_flags & CLONE_VFORK) {
- if (current->ptrace & PT_TRACE_VFORK)
- return PTRACE_EVENT_VFORK;
- } else if ((clone_flags & CSIGNAL) != SIGCHLD) {
- if (current->ptrace & PT_TRACE_CLONE)
- return PTRACE_EVENT_CLONE;
- } else if (current->ptrace & PT_TRACE_FORK)
- return PTRACE_EVENT_FORK;
+ if (clone_flags & CLONE_VFORK)
+ event = PTRACE_EVENT_VFORK;
+ else if ((clone_flags & CSIGNAL) != SIGCHLD)
+ event = PTRACE_EVENT_CLONE;
+ else
+ event = PTRACE_EVENT_FORK;

- return 0;
+ return ptrace_event_enabled(current, event) ? event : 0;
}

/**
@@ -318,7 +318,7 @@ static inline void tracehook_report_clone_complete(int trace,
struct task_struct *child)
{
if (unlikely(trace))
- ptrace_event(0, trace, pid);
+ ptrace_event(trace, pid);
}

/**
@@ -336,7 +336,7 @@ static inline void tracehook_report_clone_complete(int trace,
static inline void tracehook_report_vfork_done(struct task_struct *child,
pid_t pid)
{
- ptrace_event(PT_TRACE_VFORK_DONE, PTRACE_EVENT_VFORK_DONE, pid);
+ ptrace_event(PTRACE_EVENT_VFORK_DONE, pid);
}

/**
--
1.7.5.4


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