[4.2.y-ckt stable] Patch "x86/signal: Fix restart_syscall number for x32 tasks" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    x86/signal: Fix restart_syscall number for x32 tasks

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt2.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From e4300341dd470a16d6ff9c5a6d6d2091592cdc37 Mon Sep 17 00:00:00 2001
From: "Dmitry V. Levin" <ldv at altlinux.org>
Date: Tue, 1 Dec 2015 00:54:36 +0300
Subject: x86/signal: Fix restart_syscall number for x32 tasks

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 at gmail.com>
Signed-off-by: Dmitry V. Levin <ldv at altlinux.org>
Cc: Elvira Khabirova <lineprinter0 at gmail.com>
Link: http://lkml.kernel.org/r/20151130215436.GA25996@altlinux.org
Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/x86/kernel/signal.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 71820c4..ce10cbc 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -685,12 +685,15 @@ handle_signal(struct ksignal *ksig, struct pt_regs *regs)
 	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
@@ -719,7 +722,7 @@ static void do_signal(struct pt_regs *regs)
 			break;

 		case -ERESTART_RESTARTBLOCK:
-			regs->ax = NR_restart_syscall;
+			regs->ax = get_nr_restart_syscall(regs);
 			regs->ip -= 2;
 			break;
 		}
--
1.9.1