s390/uvdevice: Add info IOCTL

Add an IOCTL that allows userspace to find out which IOCTLs the uvdevice
supports without trial and error.

Explicitly expose the IOCTL nr for the request types.

Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Link: https://lore.kernel.org/r/20230615100533.3996107-3-seiden@linux.ibm.com
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Message-Id: <20230615100533.3996107-3-seiden@linux.ibm.com>

Author: steffen-eiden

arch/s390/include/uapi/asm/uvdevice.h

@@ -32,6 +32,33 @@ struct uvio_attest {
 	__u16 reserved136;				/* 0x0136 */
 };
 
+/**
+ * uvio_uvdev_info - Information of supported functions
+ * @supp_uvio_cmds - supported IOCTLs by this device
+ * @supp_uv_cmds - supported UVCs corresponding to the IOCTL
+ *
+ * UVIO request to get information about supported request types by this
+ * uvdevice and the Ultravisor.  Everything is output. Bits are in LSB0
+ * ordering.  If the bit is set in both, @supp_uvio_cmds and @supp_uv_cmds, the
+ * uvdevice and the Ultravisor support that call.
+ *
+ * Note that bit 0 (UVIO_IOCTL_UVDEV_INFO_NR) is always zero for `supp_uv_cmds`
+ * as there is no corresponding UV-call.
+ */
+struct uvio_uvdev_info {
+	/*
+	 * If bit `n` is set, this device supports the IOCTL with nr `n`.
+	 */
+	__u64 supp_uvio_cmds;
+	/*
+	 * If bit `n` is set, the Ultravisor(UV) supports the UV-call
+	 * corresponding to the IOCTL with nr `n` in the calling contextx (host
+	 * or guest).  The value is only valid if the corresponding bit in
+	 * @supp_uvio_cmds is set as well.
+	 */
+	__u64 supp_uv_cmds;
+};
+
 /*
  * The following max values define an upper length for the IOCTL in/out buffers.
  * However, they do not represent the maximum the Ultravisor allows which is
@@ -46,6 +73,19 @@ struct uvio_attest {
 #define UVIO_DEVICE_NAME "uv"
 #define UVIO_TYPE_UVC 'u'
 
-#define UVIO_IOCTL_ATT _IOWR(UVIO_TYPE_UVC, 0x01, struct uvio_ioctl_cb)
+enum UVIO_IOCTL_NR {
+	UVIO_IOCTL_UVDEV_INFO_NR = 0x00,
+	UVIO_IOCTL_ATT_NR,
+	/* must be the last entry */
+	UVIO_IOCTL_NUM_IOCTLS
+};
+
+#define UVIO_IOCTL(nr)		_IOWR(UVIO_TYPE_UVC, nr, struct uvio_ioctl_cb)
+#define UVIO_IOCTL_UVDEV_INFO	UVIO_IOCTL(UVIO_IOCTL_UVDEV_INFO_NR)
+#define UVIO_IOCTL_ATT		UVIO_IOCTL(UVIO_IOCTL_ATT_NR)
+
+#define UVIO_SUPP_CALL(nr)	(1ULL << (nr))
+#define UVIO_SUPP_UDEV_INFO	UVIO_SUPP_CALL(UVIO_IOCTL_UDEV_INFO_NR)
+#define UVIO_SUPP_ATT		UVIO_SUPP_CALL(UVIO_IOCTL_ATT_NR)
 
 #endif /* __S390_ASM_UVDEVICE_H */

drivers/s390/char/Kconfig

@@ -96,7 +96,7 @@ config SCLP_OFB
 config S390_UV_UAPI
 	def_tristate m
 	prompt "Ultravisor userspace API"
-	depends on S390
+	depends on S390 && (KVM || PROTECTED_VIRTUALIZATION_GUEST)
 	help
 	  Selecting exposes parts of the UV interface to userspace
 	  by providing a misc character device at /dev/uv.

drivers/s390/char/uvdevice.c

@@ -32,6 +32,52 @@
 #include <asm/uvdevice.h>
 #include <asm/uv.h>
 
+#define BIT_UVIO_INTERNAL U32_MAX
+/* Mapping from IOCTL-nr to UVC-bit */
+static const u32 ioctl_nr_to_uvc_bit[] __initconst = {
+	[UVIO_IOCTL_UVDEV_INFO_NR] = BIT_UVIO_INTERNAL,
+	[UVIO_IOCTL_ATT_NR] = BIT_UVC_CMD_RETR_ATTEST,
+};
+
+static_assert(ARRAY_SIZE(ioctl_nr_to_uvc_bit) == UVIO_IOCTL_NUM_IOCTLS);
+
+static struct uvio_uvdev_info uvdev_info = {
+	.supp_uvio_cmds = GENMASK_ULL(UVIO_IOCTL_NUM_IOCTLS - 1, 0),
+};
+
+static void __init set_supp_uv_cmds(unsigned long *supp_uv_cmds)
+{
+	int i;
+
+	for (i = 0; i < UVIO_IOCTL_NUM_IOCTLS; i++) {
+		if (ioctl_nr_to_uvc_bit[i] == BIT_UVIO_INTERNAL)
+			continue;
+		if (!test_bit_inv(ioctl_nr_to_uvc_bit[i], uv_info.inst_calls_list))
+			continue;
+		__set_bit(i, supp_uv_cmds);
+	}
+}
+
+/**
+ * uvio_uvdev_info() - get information about the uvdevice
+ *
+ * @uv_ioctl: ioctl control block
+ *
+ * Lists all IOCTLs that are supported by this uvdevice
+ */
+static int uvio_uvdev_info(struct uvio_ioctl_cb *uv_ioctl)
+{
+	void __user *user_buf_arg = (void __user *)uv_ioctl->argument_addr;
+
+	if (uv_ioctl->argument_len < sizeof(uvdev_info))
+		return -EINVAL;
+	if (copy_to_user(user_buf_arg, &uvdev_info, sizeof(uvdev_info)))
+		return -EFAULT;
+
+	uv_ioctl->uv_rc = UVC_RC_EXECUTED;
+	return 0;
+}
+
 static int uvio_build_uvcb_attest(struct uv_cb_attest *uvcb_attest, u8 *arcb,
 				  u8 *meas, u8 *add_data, struct uvio_attest *uvio_attest)
 {
@@ -185,16 +231,27 @@ static int uvio_attestation(struct uvio_ioctl_cb *uv_ioctl)
 	return ret;
 }
 
-static int uvio_copy_and_check_ioctl(struct uvio_ioctl_cb *ioctl, void __user *argp)
+static int uvio_copy_and_check_ioctl(struct uvio_ioctl_cb *ioctl, void __user *argp,
+				     unsigned long cmd)
 {
+	u8 nr = _IOC_NR(cmd);
+
+	if (_IOC_DIR(cmd) != (_IOC_READ | _IOC_WRITE))
+		return -ENOIOCTLCMD;
+	if (_IOC_TYPE(cmd) != UVIO_TYPE_UVC)
+		return -ENOIOCTLCMD;
+	if (nr >= UVIO_IOCTL_NUM_IOCTLS)
+		return -ENOIOCTLCMD;
+	if (_IOC_SIZE(cmd) != sizeof(*ioctl))
+		return -ENOIOCTLCMD;
 	if (copy_from_user(ioctl, argp, sizeof(*ioctl)))
 		return -EFAULT;
 	if (ioctl->flags != 0)
 		return -EINVAL;
 	if (memchr_inv(ioctl->reserved14, 0, sizeof(ioctl->reserved14)))
 		return -EINVAL;
 
-	return 0;
+	return nr;
 }
 
 /*
@@ -205,12 +262,17 @@ static long uvio_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 	void __user *argp = (void __user *)arg;
 	struct uvio_ioctl_cb uv_ioctl = { };
 	long ret;
+	int nr;
+
+	nr = uvio_copy_and_check_ioctl(&uv_ioctl, argp, cmd);
+	if (nr < 0)
+		return nr;
 
-	switch (cmd) {
-	case UVIO_IOCTL_ATT:
-		ret = uvio_copy_and_check_ioctl(&uv_ioctl, argp);
-		if (ret)
-			return ret;
+	switch (nr) {
+	case UVIO_IOCTL_UVDEV_INFO_NR:
+		ret = uvio_uvdev_info(&uv_ioctl);
+		break;
+	case UVIO_IOCTL_ATT_NR:
 		ret = uvio_attestation(&uv_ioctl);
 		break;
 	default:
@@ -245,6 +307,7 @@ static void __exit uvio_dev_exit(void)
 
 static int __init uvio_dev_init(void)
 {
+	set_supp_uv_cmds((unsigned long *)&uvdev_info.supp_uv_cmds);
 	return misc_register(&uvio_dev_miscdev);
 }