[PATCH v19 02/14] arm64: ptrace: Rework audit_syscall_entry()

Extract syscall_enter_audit() helper and switch to generic helpers to
get syscall number and syscall arguments, matching the generic entry
implementation.

The new code:
- Checks audit_context() first to avoid unnecessary work when audit
  is not active.
- Use syscall_get_arguments() helper instead of directly accessing
  regs fields.
- Use syscall_get_nr() helper to get syscall number instead of directly
  accessing regs->syscallno.
- Now exactly equivalent to generic entry's syscall_enter_audit().

This is a preparation step for converting arm64 to the generic entry
infrastructure. No functional changes intended.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Ada Couprie Diaz <redacted>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Reviewed-by: Yeoreum Yun <redacted>
Reviewed-by: Kevin Brodsky <redacted>
Signed-off-by: Jinjie Ruan <redacted>
---
 arch/arm64/kernel/ptrace.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 96462de75d4b..573b5770698f 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c

@@ -2458,6 +2458,19 @@ static void report_syscall_exit(struct pt_regs *regs)
 	}
 }
 
+#ifdef CONFIG_AUDITSYSCALL
+static inline void syscall_enter_audit(struct pt_regs *regs)
+{
+	long syscall = syscall_get_nr(current, regs);
+	unsigned long args[6];
+
+	syscall_get_arguments(current, regs, args);
+	__audit_syscall_entry(syscall, args[0], args[1], args[2], args[3]);
+}
+#else
+static inline void syscall_enter_audit(struct pt_regs *regs) { }
+#endif
+
 int syscall_trace_enter(struct pt_regs *regs)
 {
 	unsigned long flags = read_thread_flags();

@@ -2476,8 +2489,8 @@ int syscall_trace_enter(struct pt_regs *regs)
 	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
 		trace_sys_enter(regs, regs->syscallno);
 
-	audit_syscall_entry(regs->syscallno, regs->orig_x0, regs->regs[1],
-			    regs->regs[2], regs->regs[3]);
+	if (unlikely(audit_context()))
+		syscall_enter_audit(regs);
 
 	return regs->syscallno;
 }

-- 
2.34.1