From 9057f54d74eae13757b4bf295ff9ed8fd9a2673a Mon Sep 17 00:00:00 2001
From: Warner Losh <imp@FreeBSD.org>
Date: Tue, 8 Aug 2017 20:44:16 +0000
Subject: [PATCH] Fail to open efirt device when no EFI on system.

libefivar expects opening /dev/efi to indicate if the we can make efi
runtime calls. With a null routine, it was always succeeding leading
efi_variables_supported() to return the wrong value. Only succeed if
we have an efi_runtime table. Also, while I'm hear, out of an
abundance of caution, add a likely redundant check to make sure
efi_systbl is not NULL before dereferencing it. I know it can't be
NULL if efi_cfgtbl is non-NULL, but the compiler doesn't.
---
 sys/amd64/amd64/efirt.c | 11 ++++++++++-
 sys/amd64/include/efi.h |  1 +
 sys/dev/efidev/efidev.c | 13 +++++++++++++
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/sys/amd64/amd64/efirt.c b/sys/amd64/amd64/efirt.c
index 94229db1f9ee..ea940d771c51 100644
--- a/sys/amd64/amd64/efirt.c
+++ b/sys/amd64/amd64/efirt.c
@@ -420,13 +420,22 @@ efi_uninit(void)
 	mtx_destroy(&efi_lock);
 }
 
+int
+efi_rt_ok(void)
+{
+
+	if (efi_runtime == NULL)
+		return (ENXIO);
+	return (0);
+}
+
 int
 efi_get_table(struct uuid *uuid, void **ptr)
 {
 	struct efi_cfgtbl *ct;
 	u_long count;
 
-	if (efi_cfgtbl == NULL)
+	if (efi_cfgtbl == NULL || efi_systbl == NULL)
 		return (ENXIO);
 	count = efi_systbl->st_entries;
 	ct = efi_cfgtbl;
diff --git a/sys/amd64/include/efi.h b/sys/amd64/include/efi.h
index a0a39b4056e9..c29a1a4d09a8 100644
--- a/sys/amd64/include/efi.h
+++ b/sys/amd64/include/efi.h
@@ -49,6 +49,7 @@
 struct uuid;
 struct efi_tm;
 
+int efi_rt_ok(void);
 int efi_get_table(struct uuid *uuid, void **ptr);
 int efi_get_time(struct efi_tm *tm);
 int efi_get_time_locked(struct efi_tm *tm);
diff --git a/sys/dev/efidev/efidev.c b/sys/dev/efidev/efidev.c
index d6e0e06468e5..1b83d55d511c 100644
--- a/sys/dev/efidev/efidev.c
+++ b/sys/dev/efidev/efidev.c
@@ -39,14 +39,27 @@ __FBSDID("$FreeBSD$");
 #include <machine/efi.h>
 #include <sys/efiio.h>
 
+static d_open_t efidev_open;
 static d_ioctl_t efidev_ioctl;
 
 static struct cdevsw efi_cdevsw = {
 	.d_name = "efi",
 	.d_version = D_VERSION,
+	.d_open = efidev_open,
 	.d_ioctl = efidev_ioctl,
 };
 	
+static int
+efidev_open(struct cdev *dev __unused, int oflags __unused,
+    int devtype __unused, struct thread *td __unused)
+{
+	/*
+	 * Only return success when we have an actual runtime to call.
+	 */
+
+	return efi_rt_ok();
+}
+
 static int
 efidev_ioctl(struct cdev *dev __unused, u_long cmd, caddr_t addr,
     int flags __unused, struct thread *td __unused)