static int branch_type()

in events/intel/lbr.c [1166:1329]

• 111 lines of code
• 42 McCabe index (conditional complexity)

static int branch_type(unsigned long from, unsigned long to, int abort)
{
	struct insn insn;
	void *addr;
	int bytes_read, bytes_left;
	int ret = X86_BR_NONE;
	int ext, to_plm, from_plm;
	u8 buf[MAX_INSN_SIZE];
	int is64 = 0;

	to_plm = kernel_ip(to) ? X86_BR_KERNEL : X86_BR_USER;
	from_plm = kernel_ip(from) ? X86_BR_KERNEL : X86_BR_USER;

	/*
	 * maybe zero if lbr did not fill up after a reset by the time
	 * we get a PMU interrupt
	 */
	if (from == 0 || to == 0)
		return X86_BR_NONE;

	if (abort)
		return X86_BR_ABORT | to_plm;

	if (from_plm == X86_BR_USER) {
		/*
		 * can happen if measuring at the user level only
		 * and we interrupt in a kernel thread, e.g., idle.
		 */
		if (!current->mm)
			return X86_BR_NONE;

		/* may fail if text not present */
		bytes_left = copy_from_user_nmi(buf, (void __user *)from,
						MAX_INSN_SIZE);
		bytes_read = MAX_INSN_SIZE - bytes_left;
		if (!bytes_read)
			return X86_BR_NONE;

		addr = buf;
	} else {
		/*
		 * The LBR logs any address in the IP, even if the IP just
		 * faulted. This means userspace can control the from address.
		 * Ensure we don't blindly read any address by validating it is
		 * a known text address.
		 */
		if (kernel_text_address(from)) {
			addr = (void *)from;
			/*
			 * Assume we can get the maximum possible size
			 * when grabbing kernel data.  This is not
			 * _strictly_ true since we could possibly be
			 * executing up next to a memory hole, but
			 * it is very unlikely to be a problem.
			 */
			bytes_read = MAX_INSN_SIZE;
		} else {
			return X86_BR_NONE;
		}
	}

	/*
	 * decoder needs to know the ABI especially
	 * on 64-bit systems running 32-bit apps
	 */
#ifdef CONFIG_X86_64
	is64 = kernel_ip((unsigned long)addr) || any_64bit_mode(current_pt_regs());
#endif
	insn_init(&insn, addr, bytes_read, is64);
	if (insn_get_opcode(&insn))
		return X86_BR_ABORT;

	switch (insn.opcode.bytes[0]) {
	case 0xf:
		switch (insn.opcode.bytes[1]) {
		case 0x05: /* syscall */
		case 0x34: /* sysenter */
			ret = X86_BR_SYSCALL;
			break;
		case 0x07: /* sysret */
		case 0x35: /* sysexit */
			ret = X86_BR_SYSRET;
			break;
		case 0x80 ... 0x8f: /* conditional */
			ret = X86_BR_JCC;
			break;
		default:
			ret = X86_BR_NONE;
		}
		break;
	case 0x70 ... 0x7f: /* conditional */
		ret = X86_BR_JCC;
		break;
	case 0xc2: /* near ret */
	case 0xc3: /* near ret */
	case 0xca: /* far ret */
	case 0xcb: /* far ret */
		ret = X86_BR_RET;
		break;
	case 0xcf: /* iret */
		ret = X86_BR_IRET;
		break;
	case 0xcc ... 0xce: /* int */
		ret = X86_BR_INT;
		break;
	case 0xe8: /* call near rel */
		if (insn_get_immediate(&insn) || insn.immediate1.value == 0) {
			/* zero length call */
			ret = X86_BR_ZERO_CALL;
			break;
		}
		fallthrough;
	case 0x9a: /* call far absolute */
		ret = X86_BR_CALL;
		break;
	case 0xe0 ... 0xe3: /* loop jmp */
		ret = X86_BR_JCC;
		break;
	case 0xe9 ... 0xeb: /* jmp */
		ret = X86_BR_JMP;
		break;
	case 0xff: /* call near absolute, call far absolute ind */
		if (insn_get_modrm(&insn))
			return X86_BR_ABORT;

		ext = (insn.modrm.bytes[0] >> 3) & 0x7;
		switch (ext) {
		case 2: /* near ind call */
		case 3: /* far ind call */
			ret = X86_BR_IND_CALL;
			break;
		case 4:
		case 5:
			ret = X86_BR_IND_JMP;
			break;
		}
		break;
	default:
		ret = X86_BR_NONE;
	}
	/*
	 * interrupts, traps, faults (and thus ring transition) may
	 * occur on any instructions. Thus, to classify them correctly,
	 * we need to first look at the from and to priv levels. If they
	 * are different and to is in the kernel, then it indicates
	 * a ring transition. If the from instruction is not a ring
	 * transition instr (syscall, systenter, int), then it means
	 * it was a irq, trap or fault.
	 *
	 * we have no way of detecting kernel to kernel faults.
	 */
	if (from_plm == X86_BR_USER && to_plm == X86_BR_KERNEL
	    && ret != X86_BR_SYSCALL && ret != X86_BR_INT)
		ret = X86_BR_IRQ;

	/*
	 * branch priv level determined by target as
	 * is done by HW when LBR_SELECT is implemented
	 */
	if (ret != X86_BR_NONE)
		ret |= to_plm;

	return ret;
}