s390/signal: remove sigreturn on stack

{rt_}sigreturn is now called from the vdso, so we no longer
need the svc on the stack, and therefore no hack to support that
mechanism on machines with non-executable stack.
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/include/asm/entry-common.h

@@ -14,7 +14,6 @@
 #define ARCH_EXIT_TO_USER_MODE_WORK (_TIF_GUARDED_STORAGE | _TIF_PER_TRAP)
 
 void do_per_trap(struct pt_regs *regs);
-void do_syscall(struct pt_regs *regs);
 
 #ifdef CONFIG_DEBUG_ENTRY
 static __always_inline void arch_check_user_regs(struct pt_regs *regs)

arch/s390/kernel/syscall.c

@@ -108,7 +108,7 @@ SYSCALL_DEFINE0(ni_syscall)
 	return -ENOSYS;
 }
 
-void do_syscall(struct pt_regs *regs)
+static void do_syscall(struct pt_regs *regs)
 {
 	unsigned long nr;
 

arch/s390/kernel/traps.c

@@ -301,10 +301,9 @@ static void (*pgm_check_table[128])(struct pt_regs *regs);
 void noinstr __do_pgm_check(struct pt_regs *regs)
 {
 	unsigned long last_break = S390_lowcore.breaking_event_addr;
-	unsigned int trapnr, syscall_redirect = 0;
+	unsigned int trapnr;
 	irqentry_state_t state;
 
-	add_random_kstack_offset();
 	regs->int_code = *(u32 *)&S390_lowcore.pgm_ilc;
 	regs->int_parm_long = S390_lowcore.trans_exc_code;
 
@@ -346,18 +345,9 @@ void noinstr __do_pgm_check(struct pt_regs *regs)
 	trapnr = regs->int_code & PGM_INT_CODE_MASK;
 	if (trapnr)
 		pgm_check_table[trapnr](regs);
-	syscall_redirect = user_mode(regs) && test_pt_regs_flag(regs, PIF_SYSCALL);
 out:
 	local_irq_disable();
 	irqentry_exit(regs, state);
-
-	if (syscall_redirect) {
-		enter_from_user_mode(regs);
-		local_irq_enable();
-		regs->orig_gpr2 = regs->gprs[2];
-		do_syscall(regs);
-		exit_to_user_mode();
-	}
 }
 
 /*

arch/s390/mm/fault.c

@@ -285,26 +285,6 @@ static noinline void do_sigbus(struct pt_regs *regs)
 			(void __user *)(regs->int_parm_long & __FAIL_ADDR_MASK));
 }
 
-static noinline int signal_return(struct pt_regs *regs)
-{
-	u16 instruction;
-	int rc;
-
-	rc = __get_user(instruction, (u16 __user *) regs->psw.addr);
-	if (rc)
-		return rc;
-	if (instruction == 0x0a77) {
-		set_pt_regs_flag(regs, PIF_SYSCALL);
-		regs->int_code = 0x00040077;
-		return 0;
-	} else if (instruction == 0x0aad) {
-		set_pt_regs_flag(regs, PIF_SYSCALL);
-		regs->int_code = 0x000400ad;
-		return 0;
-	}
-	return -EACCES;
-}
-
 static noinline void do_fault_error(struct pt_regs *regs, int access,
 					vm_fault_t fault)
 {
@@ -312,9 +292,6 @@ static noinline void do_fault_error(struct pt_regs *regs, int access,
 
 	switch (fault) {
 	case VM_FAULT_BADACCESS:
-		if (access == VM_EXEC && signal_return(regs) == 0)
-			break;
-		fallthrough;
 	case VM_FAULT_BADMAP:
 		/* Bad memory access. Check if it is kernel or user space. */
 		if (user_mode(regs)) {