s390: support KPROBES_ON_FTRACE

Instead of using our own kprobes-on-ftrace handling convert the
code to support KPROBES_ON_FTRACE.

Signed-off-by: Sven Schnelle <[e-mail]>
Signed-off-by: Vasily Gorbik <[e-mail]>

Documentation/features/debug/kprobes-on-ftrace/arch-support.txt

···
     |      parisc: |  ok  |
     |     powerpc: |  ok  |
     |       riscv: | TODO |
-    |        s390: | TODO |
+    |        s390: |  ok  |
     |          sh: | TODO |
     |       sparc: | TODO |
     |          um: | TODO |

arch/s390/Kconfig

···
 	select HAVE_KERNEL_UNCOMPRESSED
 	select HAVE_KERNEL_XZ
 	select HAVE_KPROBES
+	select HAVE_KPROBES_ON_FTRACE
 	select HAVE_KRETPROBES
 	select HAVE_KVM
 	select HAVE_LIVEPATCH

arch/s390/include/asm/kprobes.h

···
 struct arch_specific_insn {
 	/* copy of original instruction */
 	kprobe_opcode_t *insn;
-	unsigned int is_ftrace_insn : 1;
 };
 
 struct prev_kprobe {

arch/s390/kernel/ftrace.c

···
 #endif
 }
 
-static inline int is_kprobe_on_ftrace(struct ftrace_insn *insn)
-{
-#ifdef CONFIG_KPROBES
-	if (insn->opc == BREAKPOINT_INSTRUCTION)
-		return 1;
-#endif
-	return 0;
-}
-
 static inline void ftrace_generate_kprobe_nop_insn(struct ftrace_insn *insn)
 {
 #ifdef CONFIG_KPROBES
···
 		/* Initial code replacement */
 		ftrace_generate_orig_insn(&orig);
 		ftrace_generate_nop_insn(&new);
-	} else if (is_kprobe_on_ftrace(&old)) {
-		/*
-		 * If we find a breakpoint instruction, a kprobe has been
-		 * placed at the beginning of the function. We write the
-		 * constant KPROBE_ON_FTRACE_NOP into the remaining four
-		 * bytes of the original instruction so that the kprobes
-		 * handler can execute a nop, if it reaches this breakpoint.
-		 */
-		ftrace_generate_kprobe_call_insn(&orig);
-		ftrace_generate_kprobe_nop_insn(&new);
 	} else {
 		/* Replace ftrace call with a nop. */
 		ftrace_generate_call_insn(&orig, rec->ip);
···
 
 	if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old)))
 		return -EFAULT;
-	if (is_kprobe_on_ftrace(&old)) {
-		/*
-		 * If we find a breakpoint instruction, a kprobe has been
-		 * placed at the beginning of the function. We write the
-		 * constant KPROBE_ON_FTRACE_CALL into the remaining four
-		 * bytes of the original instruction so that the kprobes
-		 * handler can execute a brasl if it reaches this breakpoint.
-		 */
-		ftrace_generate_kprobe_nop_insn(&orig);
-		ftrace_generate_kprobe_call_insn(&new);
-	} else {
-		/* Replace nop with an ftrace call. */
-		ftrace_generate_nop_insn(&orig);
-		ftrace_generate_call_insn(&new, rec->ip);
-	}
+	/* Replace nop with an ftrace call. */
+	ftrace_generate_nop_insn(&orig);
+	ftrace_generate_call_insn(&new, rec->ip);
+
 	/* Verify that the to be replaced code matches what we expect. */
 	if (memcmp(&orig, &old, sizeof(old)))
 		return -EINVAL;
···
 }
 
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+
+#ifdef CONFIG_KPROBES_ON_FTRACE
+void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
+		struct ftrace_ops *ops, struct pt_regs *regs)
+{
+	struct kprobe_ctlblk *kcb;
+	struct kprobe *p = get_kprobe((kprobe_opcode_t *)ip);
+
+	if (unlikely(!p) || kprobe_disabled(p))
+		return;
+
+	if (kprobe_running()) {
+		kprobes_inc_nmissed_count(p);
+		return;
+	}
+
+	__this_cpu_write(current_kprobe, p);
+
+	kcb = get_kprobe_ctlblk();
+	kcb->kprobe_status = KPROBE_HIT_ACTIVE;
+
+	instruction_pointer_set(regs, ip);
+
+	if (!p->pre_handler || !p->pre_handler(p, regs)) {
+
+		instruction_pointer_set(regs, ip + MCOUNT_INSN_SIZE);
+
+		if (unlikely(p->post_handler)) {
+			kcb->kprobe_status = KPROBE_HIT_SSDONE;
+			p->post_handler(p, regs, 0);
+		}
+	}
+	__this_cpu_write(current_kprobe, NULL);
+}
+NOKPROBE_SYMBOL(kprobe_ftrace_handler);
+
+int arch_prepare_kprobe_ftrace(struct kprobe *p)
+{
+	p->ainsn.insn = NULL;
+	return 0;
+}
+#endif

arch/s390/kernel/kprobes.c

···
 
 static void copy_instruction(struct kprobe *p)
 {
-	unsigned long ip = (unsigned long) p->addr;
 	s64 disp, new_disp;
 	u64 addr, new_addr;
 
-	if (ftrace_location(ip) == ip) {
-		/*
-		 * If kprobes patches the instruction that is morphed by
-		 * ftrace make sure that kprobes always sees the branch
-		 * "jg .+24" that skips the mcount block or the "brcl 0,0"
-		 * in case of hotpatch.
-		 */
-		ftrace_generate_nop_insn((struct ftrace_insn *)p->ainsn.insn);
-		p->ainsn.is_ftrace_insn = 1;
-	} else
-		memcpy(p->ainsn.insn, p->addr, insn_length(*p->addr >> 8));
+	memcpy(p->ainsn.insn, p->addr, insn_length(*p->addr >> 8));
 	p->opcode = p->ainsn.insn[0];
 	if (!probe_is_insn_relative_long(p->ainsn.insn))
 		return;
···
 }
 NOKPROBE_SYMBOL(arch_prepare_kprobe);
 
-int arch_check_ftrace_location(struct kprobe *p)
-{
-	return 0;
-}
-
 struct swap_insn_args {
 	struct kprobe *p;
 	unsigned int arm_kprobe : 1;
···
 static int swap_instruction(void *data)
 {
 	struct swap_insn_args *args = data;
-	struct ftrace_insn new_insn, *insn;
 	struct kprobe *p = args->p;
-	size_t len;
+	u16 opc;
 
-	new_insn.opc = args->arm_kprobe ? BREAKPOINT_INSTRUCTION : p->opcode;
-	len = sizeof(new_insn.opc);
-	if (!p->ainsn.is_ftrace_insn)
-		goto skip_ftrace;
-	len = sizeof(new_insn);
-	insn = (struct ftrace_insn *) p->addr;
-	if (args->arm_kprobe) {
-		if (is_ftrace_nop(insn))
-			new_insn.disp = KPROBE_ON_FTRACE_NOP;
-		else
-			new_insn.disp = KPROBE_ON_FTRACE_CALL;
-	} else {
-		ftrace_generate_call_insn(&new_insn, (unsigned long)p->addr);
-		if (insn->disp == KPROBE_ON_FTRACE_NOP)
-			ftrace_generate_nop_insn(&new_insn);
-	}
-skip_ftrace:
-	s390_kernel_write(p->addr, &new_insn, len);
+	opc = args->arm_kprobe ? BREAKPOINT_INSTRUCTION : p->opcode;
+	s390_kernel_write(p->addr, &opc, sizeof(opc));
 	return 0;
 }
 NOKPROBE_SYMBOL(swap_instruction);
···
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 	unsigned long ip = regs->psw.addr;
 	int fixup = probe_get_fixup_type(p->ainsn.insn);
-
-	/* Check if the kprobes location is an enabled ftrace caller */
-	if (p->ainsn.is_ftrace_insn) {
-		struct ftrace_insn *insn = (struct ftrace_insn *) p->addr;
-		struct ftrace_insn call_insn;
-
-		ftrace_generate_call_insn(&call_insn, (unsigned long) p->addr);
-		/*
-		 * A kprobe on an enabled ftrace call site actually single
-		 * stepped an unconditional branch (ftrace nop equivalent).
-		 * Now we need to fixup things and pretend that a brasl r0,...
-		 * was executed instead.
-		 */
-		if (insn->disp == KPROBE_ON_FTRACE_CALL) {
-			ip += call_insn.disp * 2 - MCOUNT_INSN_SIZE;
-			regs->gprs[0] = (unsigned long)p->addr + sizeof(*insn);
-		}
-	}
 
 	if (fixup & FIXUP_PSW_NORMAL)
 		ip += (unsigned long) p->addr - (unsigned long) p->ainsn.insn;

arch/s390/kernel/mcount.S

···
 	.globl	ftrace_regs_caller
 	.set	ftrace_regs_caller,ftrace_caller
 	stg	%r14,(__SF_GPRS+8*8)(%r15)	# save traced function caller
+	lghi	%r14,0				# save condition code
+	ipm	%r14				# don't put any instructions
+	sllg	%r14,%r14,16			# clobbering CC before this point
 	lgr	%r1,%r15
 #if !(defined(CC_USING_HOTPATCH) || defined(CC_USING_NOP_MCOUNT))
 	aghi	%r0,MCOUNT_RETURN_FIXUP
···
 	# allocate pt_regs and stack frame for ftrace_trace_function
 	aghi	%r15,-STACK_FRAME_SIZE
 	stg	%r1,(STACK_PTREGS_GPRS+15*8)(%r15)
+	stg	%r14,(STACK_PTREGS_PSW)(%r15)
+	lg	%r14,(__SF_GPRS+8*8)(%r1)	# restore original return address
+	stosm	(STACK_PTREGS_PSW)(%r15),0
 	aghi	%r1,-TRACED_FUNC_FRAME_SIZE
 	stg	%r1,__SF_BACKCHAIN(%r15)
 	stg	%r0,(STACK_PTREGS_PSW+8)(%r15)