arm64: read thread flags

Some thread flags can be set remotely, and so even when IRQs are
disabled, the flags can change under our feet. Generally this is
unlikely to cause a problem in practice, but it is somewhat unsound, and
KCSAN will legitimately warn that there is a data race.

To avoid such issues, we should snapshot the flags prior to using them.
Let's use the new helpers to do so on arm64.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>

arch/arm64/kernel/ptrace.c

@@ -1834,7 +1834,7 @@ static void tracehook_report_syscall(struct pt_regs *regs,
 
 int syscall_trace_enter(struct pt_regs *regs)
 {
-	unsigned long flags = READ_ONCE(current_thread_info()->flags);
+	unsigned long flags = read_thread_flags();
 
 	if (flags & (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE)) {
 		tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);
@@ -1857,7 +1857,7 @@ int syscall_trace_enter(struct pt_regs *regs)
 
 void syscall_trace_exit(struct pt_regs *regs)
 {
-	unsigned long flags = READ_ONCE(current_thread_info()->flags);
+	unsigned long flags = read_thread_flags();
 
 	audit_syscall_exit(regs);
 

arch/arm64/kernel/signal.c

@@ -971,7 +971,7 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
 		}
 
 		local_daif_mask();
-		thread_flags = READ_ONCE(current_thread_info()->flags);
+		thread_flags = read_thead_flags();
 	} while (thread_flags & _TIF_WORK_MASK);
 }
 

arch/arm64/kernel/syscall.c

@@ -84,7 +84,7 @@ void syscall_trace_exit(struct pt_regs *regs);
 static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
 			   const syscall_fn_t syscall_table[])
 {
-	unsigned long flags = current_thread_info()->flags;
+	unsigned long flags = read_thread_flags();
 
 	regs->orig_x0 = regs->regs[0];
 	regs->syscallno = scno;
@@ -151,7 +151,7 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
 	 */
 	if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) {
 		local_daif_mask();
-		flags = current_thread_info()->flags;
+		flags = read_thread_flags();
 		if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP))
 			return;
 		local_daif_restore(DAIF_PROCCTX);