signal: Simplify tracehook_report_syscall_exit

Replace user_single_step_siginfo with user_single_step_report
that allocates siginfo structure on the stack and sends it.

This allows tracehook_report_syscall_exit to become a simple
if statement that calls user_single_step_report or ptrace_report_syscall
depending on the value of step.

Update the default helper function now called user_single_step_report
to explicitly set si_code to SI_USER and to set si_uid and si_pid to 0.
The default helper has always been doing this (using memset) but it
was far from obvious.

The powerpc helper can now just call force_sig_fault.
The x86 helper can now just call send_sigtrap.

Unfortunately the default implementation of user_single_step_report
can not use force_sig_fault as it does not use a SIGTRAP si_code.
So it has to carefully setup the siginfo and use use force_sig_info.

The net result is code that is easier to understand and simpler
to maintain.

Ref: 85ec7fd9f8e5 ("ptrace: introduce user_single_step_siginfo() helper")
Reviewed-by: Thomas Gleixner <[e-mail]>
Signed-off-by: "Eric W. Biederman" <[e-mail]>

arch/powerpc/include/asm/ptrace.h

···
 
 #define arch_has_single_step()	(1)
 #define arch_has_block_step()	(!cpu_has_feature(CPU_FTR_601))
-#define ARCH_HAS_USER_SINGLE_STEP_INFO
+#define ARCH_HAS_USER_SINGLE_STEP_REPORT
 
 /*
  * kprobe-based event tracer support

arch/powerpc/kernel/traps.c

···
 }
 NOKPROBE_SYMBOL(die);
 
-void user_single_step_siginfo(struct task_struct *tsk,
-				struct pt_regs *regs, siginfo_t *info)
+void user_single_step_report(struct pt_regs *regs)
 {
-	info->si_signo = SIGTRAP;
-	info->si_code = TRAP_TRACE;
-	info->si_addr = (void __user *)regs->nip;
+	force_sig_fault(SIGTRAP, TRAP_TRACE, (void __user *)regs->nip, current);
 }
 
 static void show_signal_msg(int signr, struct pt_regs *regs, int code,

arch/x86/include/asm/ptrace.h

···
 #define arch_has_block_step()	(boot_cpu_data.x86 >= 6)
 #endif
 
-#define ARCH_HAS_USER_SINGLE_STEP_INFO
+#define ARCH_HAS_USER_SINGLE_STEP_REPORT
 
 /*
  * When hitting ptrace_stop(), we cannot return using SYSRET because

arch/x86/kernel/ptrace.c

···
 	info->si_addr = user_mode(regs) ? (void __user *)regs->ip : NULL;
 }
 
-void user_single_step_siginfo(struct task_struct *tsk,
-				struct pt_regs *regs,
-				struct siginfo *info)
-{
-	fill_sigtrap_info(tsk, regs, 0, TRAP_BRKPT, info);
-}
 
 void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs,
 					 int error_code, int si_code)
···
 	fill_sigtrap_info(tsk, regs, error_code, si_code, &info);
 	/* Send us the fake SIGTRAP */
 	force_sig_info(SIGTRAP, &info, tsk);
+}
+
+void user_single_step_report(struct pt_regs *regs)
+{
+	send_sigtrap(current, regs, 0, TRAP_BRKPT);
 }

include/linux/ptrace.h

···
 extern void user_enable_block_step(struct task_struct *);
 #endif	/* arch_has_block_step */
 
-#ifdef ARCH_HAS_USER_SINGLE_STEP_INFO
-extern void user_single_step_siginfo(struct task_struct *tsk,
-				struct pt_regs *regs, siginfo_t *info);
+#ifdef ARCH_HAS_USER_SINGLE_STEP_REPORT
+extern void user_single_step_report(struct pt_regs *regs);
 #else
-static inline void user_single_step_siginfo(struct task_struct *tsk,
-				struct pt_regs *regs, siginfo_t *info)
+static inline void user_single_step_report(struct pt_regs *regs)
 {
-	info->si_signo = SIGTRAP;
+	siginfo_t info;
+	clear_siginfo(&info);
+	info.si_signo = SIGTRAP;
+	info.si_errno = 0;
+	info.si_code = SI_USER;
+	info.si_pid = 0;
+	info.si_uid = 0;
+	force_sig_info(info.si_signo, &info, current);
 }
 #endif
 

include/linux/tracehook.h

···
  */
 static inline void tracehook_report_syscall_exit(struct pt_regs *regs, int step)
 {
-	if (step) {
-		siginfo_t info;
-		clear_siginfo(&info);
-		user_single_step_siginfo(current, regs, &info);
-		force_sig_info(SIGTRAP, &info, current);
-		return;
-	}
-
-	ptrace_report_syscall(regs);
+	if (step)
+		user_single_step_report(regs);
+	else
+		ptrace_report_syscall(regs);
 }
 
 /**