s390/ftrace: add code replacement sanity checks

int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,

		    unsigned long addr)

{

	struct ftrace_insn insn;

	unsigned short op;

	void *from, *to;

	size_t size;

	ftrace_generate_nop_insn(&insn);

	size = sizeof(insn);

	from = &insn;

	to = (void *) rec->ip;

	if (probe_kernel_read(&op, (void *) rec->ip, sizeof(op)))

	struct ftrace_insn orig, new, old;

	if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old)))

		return -EFAULT;

	if (addr == MCOUNT_ADDR) {

		/* Initial code replacement; we expect to see stg r14,8(r15) */

		orig.opc = 0xe3e0;

		orig.disp = 0xf0080024;

		ftrace_generate_nop_insn(&new);

	} else if (old.opc == BREAKPOINT_INSTRUCTION) {

		/*

	 * 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.

		 * 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.

		 */

	if (op == BREAKPOINT_INSTRUCTION) {

		size -= 2;

		from += 2;

		to += 2;

		insn.disp = KPROBE_ON_FTRACE_NOP;

		new.opc = orig.opc = BREAKPOINT_INSTRUCTION;

		orig.disp = KPROBE_ON_FTRACE_CALL;

		new.disp = KPROBE_ON_FTRACE_NOP;

	} else {

		/* Replace ftrace call with a nop. */

		ftrace_generate_call_insn(&orig, rec->ip);

		ftrace_generate_nop_insn(&new);

	}

	if (probe_kernel_write(to, from, size))

	/* Verify that the to be replaced code matches what we expect. */

	if (memcmp(&orig, &old, sizeof(old)))

		return -EINVAL;

	if (probe_kernel_write((void *) rec->ip, &new, sizeof(new)))

		return -EPERM;

	return 0;

}

int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)

{

	struct ftrace_insn insn;

	unsigned short op;

	void *from, *to;

	size_t size;

	ftrace_generate_call_insn(&insn, rec->ip);

	size = sizeof(insn);

	from = &insn;

	to = (void *) rec->ip;

	if (probe_kernel_read(&op, (void *) rec->ip, sizeof(op)))

	struct ftrace_insn orig, new, old;

	if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old)))

		return -EFAULT;

	if (old.opc == BREAKPOINT_INSTRUCTION) {

		/*

	 * 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.

		 * 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.

		 */

	if (op == BREAKPOINT_INSTRUCTION) {

		size -= 2;

		from += 2;

		to += 2;

		insn.disp = KPROBE_ON_FTRACE_CALL;

		new.opc = orig.opc = BREAKPOINT_INSTRUCTION;

		orig.disp = KPROBE_ON_FTRACE_NOP;

		new.disp = KPROBE_ON_FTRACE_CALL;

	} else {

		/* Replace nop with an ftrace call. */

		ftrace_generate_nop_insn(&orig);

		ftrace_generate_call_insn(&new, rec->ip);

	}

	if (probe_kernel_write(to, from, size))

	/* Verify that the to be replaced code matches what we expect. */

	if (memcmp(&orig, &old, sizeof(old)))

		return -EINVAL;

	if (probe_kernel_write((void *) rec->ip, &new, sizeof(new)))

		return -EPERM;

	return 0;

}