[PATCH v2 1/2] s390/signal: Fix incorrect return address in signal frame

[Heiko Carstens]

exit_to_user_mode_loop() can call arch_do_signal_or_restart() multiple
times when signals are pending.

If the first call set up a vDSO system call restart by saving the real
user return address and adjusting psw.addr so it points to the vDSO stub,
a second call builds the signal frame with the wrong return address.

Restore psw.addr from arch_data, and set the return code to -EINTR before
building the signal frame.

This requires restart_block.arch_data to be properly initialized for all
tasks. Move the initialization in copy_thread() in front of the kernel
thread check, so that it also covers kernel threads and their children
(PID 1, usermode helpers). Only PID 0 is left uninitialized, since it
never returns to user space.

Fixes: df29a7440c4b ("s390/signal: switch to using vdso for sigreturn and syscall restart")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Heiko Carstens <hca@xxxxxxxxxxxxx>
---
 arch/s390/kernel/process.c | 12 ++++++------
 arch/s390/kernel/signal.c  |  6 +++++-
 2 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/arch/s390/kernel/process.c b/arch/s390/kernel/process.c
index 416650ae4871..4676a6a8257e 100644
--- a/arch/s390/kernel/process.c
+++ b/arch/s390/kernel/process.c
@@ -131,6 +131,12 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 	p->thread.hardirq_timer = 0;
 	p->thread.softirq_timer = 0;
 	p->thread.last_break = 1;
+	/*
+	 * s390 stores the svc return address in arch_data when calling
+	 * sigreturn()/restart_syscall() via vdso. 1 means no valid address
+	 * stored.
+	 */
+	p->restart_block.arch_data = 1;
 
 	frame->sf.back_chain = 0;
 	frame->sf.gprs[11 - 6] = (unsigned long)&frame->childregs;
@@ -168,12 +174,6 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 		p->thread.acrs[0] = (unsigned int)(tls >> 32);
 		p->thread.acrs[1] = (unsigned int)tls;
 	}
-	/*
-	 * s390 stores the svc return address in arch_data when calling
-	 * sigreturn()/restart_syscall() via vdso. 1 means no valid address
-	 * stored.
-	 */
-	p->restart_block.arch_data = 1;
 	return 0;
 }
 
diff --git a/arch/s390/kernel/signal.c b/arch/s390/kernel/signal.c
index 4874de5edea0..b59b0c49a1aa 100644
--- a/arch/s390/kernel/signal.c
+++ b/arch/s390/kernel/signal.c
@@ -475,7 +475,11 @@ void arch_do_signal_or_restart(struct pt_regs *regs)
 		}
 		/* No longer in a system call */
 		clear_pt_regs_flag(regs, PIF_SYSCALL);
-
+		if (!(current->restart_block.arch_data & 1)) {
+			regs->psw.addr = current->restart_block.arch_data;
+			current->restart_block.arch_data = 1;
+			regs->gprs[2] = -EINTR;
+		}
 		rseq_signal_deliver(&ksig, regs);
 		handle_signal(&ksig, oldset, regs);
 		return;
-- 
2.53.0