bhyve: tpm: Avoid printing a message when clearing the cancel bit

Some drivers do this routinely, e.g., FreeBSD's tpm20 does this every
time it sends a command in tpmcrb_transmit().  This causes the console
to fill up with messages.  Instead, only print a warning if the cancel
bit is set to one.

Reviewed by:	corvink
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D52425

1 files changed, 11 insertions, 4 deletions

diff --git a/usr.sbin/bhyve/tpm_intf_crb.c b/usr.sbin/bhyve/tpm_intf_crb.c
index d571e89bb5ae..7058b47733f3 100644
--- a/usr.sbin/bhyve/tpm_intf_crb.c
+++ b/usr.sbin/bhyve/tpm_intf_crb.c
@@ -371,11 +371,18 @@ tpm_crb_mem_handler(struct vcpu *vcpu __unused, const int dir,
 			break;
 		}
 		case offsetof(struct tpm_crb_regs, ctrl_cancel): {
-			/* TODO: cancel the tpm command */
-			warnx(
-			    "%s: cancelling a TPM command is not implemented yet",
-			    __func__);
+			union tpm_crb_reg_ctrl_cancel cancel;
+
+			if ((size_t)size > sizeof(cancel))
+				goto err_out;
 
+			tpm_crb_mmiocpy(&cancel, val, size);
+			if (cancel.cancel != 0) {
+				/* TODO: cancel the tpm command */
+				warnx(
+		    "%s: cancelling a TPM command is not implemented yet",
+				    __func__);
+			}
 			break;
 		}
 		case offsetof(struct tpm_crb_regs, int_enable):