s390/seccomp: add support for system call filtering using BPF

Signed-off-by: Heiko Carstens <[e-mail]>
Signed-off-by: Martin Schwidefsky <[e-mail]>

arch/s390/Kconfig

···
 	select GENERIC_TIME_VSYSCALL
 	select GENERIC_CLOCKEVENTS
 	select KTIME_SCALAR if 32BIT
+	select HAVE_ARCH_SECCOMP_FILTER
 
 config SCHED_OMIT_FRAME_POINTER
 	def_bool y

arch/s390/include/asm/syscall.h

···
 #ifndef _ASM_SYSCALL_H
 #define _ASM_SYSCALL_H	1
 
+#include <linux/audit.h>
 #include <linux/sched.h>
 #include <linux/err.h>
 #include <asm/ptrace.h>
···
 		regs->orig_gpr2 = args[0];
 }
 
+static inline int syscall_get_arch(struct task_struct *task,
+				   struct pt_regs *regs)
+{
+#ifdef CONFIG_COMPAT
+	if (test_tsk_thread_flag(task, TIF_31BIT))
+		return AUDIT_ARCH_S390;
+#endif
+	return sizeof(long) == 8 ? AUDIT_ARCH_S390X : AUDIT_ARCH_S390;
+}
 #endif	/* _ASM_SYSCALL_H */

arch/s390/kernel/ptrace.c

···
 	long ret = 0;
 
 	/* Do the secure computing check first. */
-	secure_computing_strict(regs->gprs[2]);
+	if (secure_computing(regs->gprs[2])) {
+		/* seccomp failures shouldn't expose any additional code. */
+		ret = -1;
+		goto out;
+	}
 
 	/*
 	 * The sysc_tracesys code in entry.S stored the system
···
 			    regs->gprs[2], regs->orig_gpr2,
 			    regs->gprs[3], regs->gprs[4],
 			    regs->gprs[5]);
+out:
 	return ret ?: regs->gprs[2];
 }