arm64: rseq: Implement backend rseq calls and select HAVE_RSEQ

Implement calls to rseq_signal_deliver, rseq_handle_notify_resume
and rseq_syscall so that we can select HAVE_RSEQ on arm64.
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/Kconfig

@@ -138,6 +138,7 @@ config ARM64
 	select HAVE_PERF_USER_STACK_DUMP
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_RCU_TABLE_FREE
+	select HAVE_RSEQ
 	select HAVE_STACKPROTECTOR
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_KPROBES

arch/arm64/include/asm/unistd.h

@@ -43,7 +43,7 @@
 #define __ARM_NR_compat_cacheflush	(__ARM_NR_COMPAT_BASE+2)
 #define __ARM_NR_compat_set_tls		(__ARM_NR_COMPAT_BASE+5)
 
-#define __NR_compat_syscalls		398
+#define __NR_compat_syscalls		399
 #endif
 
 #define __ARCH_WANT_SYS_CLONE

arch/arm64/include/asm/unistd32.h

@@ -817,6 +817,8 @@ __SYSCALL(__NR_pkey_alloc, sys_pkey_alloc)
 __SYSCALL(__NR_pkey_free, sys_pkey_free)
 #define __NR_statx 397
 __SYSCALL(__NR_statx, sys_statx)
+#define __NR_rseq 398
+__SYSCALL(__NR_rseq, sys_rseq)
 
 /*
  * Please add new compat syscalls above this comment and update

arch/arm64/kernel/entry.S

@@ -904,6 +904,7 @@ ENDPROC(el0_error)
 ret_fast_syscall:
 	disable_daif
 	str	x0, [sp, #S_X0]			// returned x0
+#ifndef CONFIG_DEBUG_RSEQ
 	ldr	x1, [tsk, #TSK_TI_FLAGS]	// re-check for syscall tracing
 	and	x2, x1, #_TIF_SYSCALL_WORK
 	cbnz	x2, ret_fast_syscall_trace
@@ -911,6 +912,7 @@ ret_fast_syscall:
 	cbnz	x2, work_pending
 	enable_step_tsk x1, x2
 	kernel_exit 0
+#endif
 ret_fast_syscall_trace:
 	enable_daif
 	b	__sys_trace_return_skipped	// we already saved x0

arch/arm64/kernel/ptrace.c

@@ -1658,6 +1658,8 @@ asmlinkage void syscall_trace_exit(struct pt_regs *regs)
 
 	if (test_thread_flag(TIF_SYSCALL_TRACE))
 		tracehook_report_syscall(regs, PTRACE_SYSCALL_EXIT);
+
+	rseq_syscall(regs);
 }
 
 /*

arch/arm64/kernel/signal.c

@@ -802,6 +802,8 @@ static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
 	int usig = ksig->sig;
 	int ret;
 
+	rseq_signal_deliver(ksig, regs);
+
 	/*
 	 * Set up the stack frame
 	 */
@@ -940,6 +942,7 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
 			if (thread_flags & _TIF_NOTIFY_RESUME) {
 				clear_thread_flag(TIF_NOTIFY_RESUME);
 				tracehook_notify_resume(regs);
+				rseq_handle_notify_resume(NULL, regs);
 			}
 
 			if (thread_flags & _TIF_FOREIGN_FPSTATE)