[PATCH RESEND v3 1/3] ptrace: pass type of a syscall-stop in ptrace_message

[Elvira Khabirova]

Define two constants, PTRACE_EVENTMSG_SYSCALL_ENTRY and
PTRACE_EVENTMSG_SYSCALL_EXIT, and place them in ptrace_message
for the duration of syscall-stops.
This way ptracers can distinguish syscall-enter-stops
from syscall-exit-stops using PTRACE_GETEVENTMSG request.

Signed-off-by: Elvira Khabirova <lineprin...@altlinux.org>
Signed-off-by: Dmitry V. Levin <l...@altlinux.org>
---
 include/linux/tracehook.h   |  9 ++++++---
 include/uapi/linux/ptrace.h | 10 ++++++++++
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
index 40b0b4c1bf7b..633a83fe7051 100644
--- a/include/linux/tracehook.h
+++ b/include/linux/tracehook.h
@@ -57,13 +57,15 @@ struct linux_binprm;
 /*
  * ptrace report for syscall entry and exit looks identical.
  */
-static inline int ptrace_report_syscall(struct pt_regs *regs)
+static inline int ptrace_report_syscall(struct pt_regs *regs,
+                                       unsigned long message)
 {
        int ptrace = current->ptrace;
 
        if (!(ptrace & PT_PTRACED))
                return 0;
 
+       current->ptrace_message = message;
        ptrace_notify(SIGTRAP | ((ptrace & PT_TRACESYSGOOD) ? 0x80 : 0));
 
        /*
@@ -76,6 +78,7 @@ static inline int ptrace_report_syscall(struct pt_regs *regs)
                current->exit_code = 0;
        }
 
+       current->ptrace_message = 0;
        return fatal_signal_pending(current);
 }
 
@@ -101,7 +104,7 @@ static inline int ptrace_report_syscall(struct pt_regs 
*regs)
 static inline __must_check int tracehook_report_syscall_entry(
        struct pt_regs *regs)
 {
-       return ptrace_report_syscall(regs);
+       return ptrace_report_syscall(regs, PTRACE_EVENTMSG_SYSCALL_ENTRY);
 }
 
 /**
@@ -126,7 +129,7 @@ static inline void tracehook_report_syscall_exit(struct 
pt_regs *regs, int step)
        if (step)
                user_single_step_report(regs);
        else
-               ptrace_report_syscall(regs);
+               ptrace_report_syscall(regs, PTRACE_EVENTMSG_SYSCALL_EXIT);
 }
 
 /**
diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h
index d5a1b8a492b9..cb138902d042 100644
--- a/include/uapi/linux/ptrace.h
+++ b/include/uapi/linux/ptrace.h
@@ -104,6 +104,16 @@ struct seccomp_metadata {
 #define PTRACE_O_MASK          (\
        0x000000ff | PTRACE_O_EXITKILL | PTRACE_O_SUSPEND_SECCOMP)
 
+/*
+ * These values are stored in task->ptrace_message by 
tracehook_report_syscall_*
+ * to describe current syscall-stop.
+ *
+ * Values for these constants are chosen so that they do not appear
+ * in task->ptrace_message by other means.
+ */
+#define PTRACE_EVENTMSG_SYSCALL_ENTRY  0x80000000U
+#define PTRACE_EVENTMSG_SYSCALL_EXIT   0x90000000U
+
 #include <asm/ptrace.h>
 
 
-- 
2.19.1