[PATCH 4.1 002/127] x86/signal: Fix restart_syscall number for x32 tasks

[Greg Kroah-Hartman]

4.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: "Dmitry V. Levin" <ldv@xxxxxxxxxxxx>

commit 22eab1108781eff09961ae7001704f7bd8fb1dce upstream.

When restarting a syscall with regs->ax == -ERESTART_RESTARTBLOCK,
regs->ax is assigned to a restart_syscall number.  For x32 tasks, this
syscall number must have __X32_SYSCALL_BIT set, otherwise it will be
an x86_64 syscall number instead of a valid x32 syscall number. This
issue has been there since the introduction of x32.

Reported-by: strace/tests/restart_syscall.test
Reported-and-tested-by: Elvira Khabirova <lineprinter0@xxxxxxxxx>
Signed-off-by: Dmitry V. Levin <ldv@xxxxxxxxxxxx>
Cc: Elvira Khabirova <lineprinter0@xxxxxxxxx>
Link: http://lkml.kernel.org/r/20151130215436.GA25996@xxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/x86/kernel/signal.c |   17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -667,12 +667,15 @@ handle_signal(struct ksignal *ksig, stru
 	signal_setup_done(failed, ksig, stepping);
 }
 
-#ifdef CONFIG_X86_32
-#define NR_restart_syscall	__NR_restart_syscall
-#else /* !CONFIG_X86_32 */
-#define NR_restart_syscall	\
-	test_thread_flag(TIF_IA32) ? __NR_ia32_restart_syscall : __NR_restart_syscall
-#endif /* CONFIG_X86_32 */
+static inline unsigned long get_nr_restart_syscall(const struct pt_regs *regs)
+{
+#if defined(CONFIG_X86_32) || !defined(CONFIG_X86_64)
+	return __NR_restart_syscall;
+#else /* !CONFIG_X86_32 && CONFIG_X86_64 */
+	return test_thread_flag(TIF_IA32) ? __NR_ia32_restart_syscall :
+		__NR_restart_syscall | (regs->orig_ax & __X32_SYSCALL_BIT);
+#endif /* CONFIG_X86_32 || !CONFIG_X86_64 */
+}
 
 /*
  * Note that 'init' is a special process: it doesn't get signals it doesn't
@@ -701,7 +704,7 @@ static void do_signal(struct pt_regs *re
 			break;
 
 		case -ERESTART_RESTARTBLOCK:
-			regs->ax = NR_restart_syscall;
+			regs->ax = get_nr_restart_syscall(regs);
 			regs->ip -= 2;
 			break;
 		}