[PATCH v9 08/16] arm64/ptrace: Do not report_syscall_exit() for PTRACE_SYSEMU_SINGLESTEP

[Jinjie Ruan]

The generic report_single_step() always returns false if SYSCALL_EMU
is set, but arm64 only checks _TIF_SINGLESTEP and does not check
_TIF_SYSCALL_EMU, which means that if both _TIF_SINGLESTEP and
_TIF_SYSCALL_EMU are set, the generic entry will not report
a single-step, whereas arm64 will do it.

As the man manual of PTRACE_SYSEMU and PTRACE_SYSEMU_SINGLESTEP said,
"For PTRACE_SYSEMU, continue and stop on entry to the next system
call, which will not be executed. For PTRACE_SYSEMU_SINGLESTEP, do the
same but also singlestep if not a system call.". And as the generic entry
report_single_step() comment said, If SYSCALL_EMU is set, then the only
reason to report is when SINGLESTEP is set (i.e. PTRACE_SYSEMU_SINGLESTEP).
Because this syscall instruction has been already reported
in syscall_trace_enter(), there is no need to report the syscall
again in syscall_exit_work().

In preparation for moving arm64 over to the generic entry code,

- Add report_single_step() helper for arm64 to make it clear.

- Do not report_syscall_exit() if both _TIF_SYSCALL_EMU and
  _TIF_SINGLESTEP set.

Signed-off-by: Jinjie Ruan <ruanjinjie at huawei.com>
---
 arch/arm64/kernel/ptrace.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 3e233968efa2..25111c121b5e 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -2414,14 +2414,25 @@ int syscall_trace_enter(struct pt_regs *regs, long syscall, unsigned long flags)
 	return syscall;
 }
 
+static inline bool report_single_step(unsigned long flags)
+{
+	if (flags & _TIF_SYSCALL_EMU)
+		return false;
+
+	return flags & _TIF_SINGLESTEP;
+}
+
 static void syscall_exit_work(struct pt_regs *regs, unsigned long flags)
 {
+	bool step;
+
 	audit_syscall_exit(regs);
 
 	if (flags & _TIF_SYSCALL_TRACEPOINT)
 		trace_sys_exit(regs, syscall_get_return_value(current, regs));
 
-	if (flags & (_TIF_SYSCALL_TRACE | _TIF_SINGLESTEP))
+	step = report_single_step(flags);
+	if (step || flags & _TIF_SYSCALL_TRACE)
 		report_syscall_exit(regs);
 }
 
-- 
2.34.1