From: Marc Zyngier <marc.zyngier@arm.com>
Date: Sun, 17 Jun 2018 10:16:21 +0100
Subject: KVM: Enforce error in ioctl for compat tasks when !KVM_COMPAT
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Git-commit: 7ddfd3e0df29106c728dda2a6bd6591ee43a4e3c
Patch-mainline: v4.18-rc2
References: bsc#1106240

The current behaviour of the compat ioctls is a bit odd.
We provide a compat_ioctl method when KVM_COMPAT is set, and NULL
otherwise. But NULL means that the normal, non-compat ioctl should
be used directly for compat tasks, and there is no way to actually
prevent a compat task from issueing KVM ioctls.

This patch changes this behaviour, by always registering a compat_ioctl
method, even if KVM_COMPAT is not selected. In that case, the callback
will always return -EINVAL.

Fixes: de8e5d744051568c8aad ("KVM: Disable compat ioctl for s390")
Reported-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Joerg Roedel <jroedel@suse.de>
---
 virt/kvm/kvm_main.c | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index ada21f47f22b..8b47507faab5 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -116,6 +116,11 @@ static long kvm_vcpu_ioctl(struct file *file, unsigned int ioctl,
 #ifdef CONFIG_KVM_COMPAT
 static long kvm_vcpu_compat_ioctl(struct file *file, unsigned int ioctl,
 				  unsigned long arg);
+#define KVM_COMPAT(c)	.compat_ioctl	= (c)
+#else
+static long kvm_no_compat_ioctl(struct file *file, unsigned int ioctl,
+				unsigned long arg) { return -EINVAL; }
+#define KVM_COMPAT(c)	.compat_ioctl	= kvm_no_compat_ioctl
 #endif
 static int hardware_enable_all(void);
 static void hardware_disable_all(void);
@@ -2396,11 +2401,9 @@ static int kvm_vcpu_release(struct inode *inode, struct file *filp)
 static struct file_operations kvm_vcpu_fops = {
 	.release        = kvm_vcpu_release,
 	.unlocked_ioctl = kvm_vcpu_ioctl,
-#ifdef CONFIG_KVM_COMPAT
-	.compat_ioctl   = kvm_vcpu_compat_ioctl,
-#endif
 	.mmap           = kvm_vcpu_mmap,
 	.llseek		= noop_llseek,
+	KVM_COMPAT(kvm_vcpu_compat_ioctl),
 };
 
 /*
@@ -2824,10 +2827,8 @@ static int kvm_device_release(struct inode *inode, struct file *filp)
 
 static const struct file_operations kvm_device_fops = {
 	.unlocked_ioctl = kvm_device_ioctl,
-#ifdef CONFIG_KVM_COMPAT
-	.compat_ioctl = kvm_device_ioctl,
-#endif
 	.release = kvm_device_release,
+	KVM_COMPAT(kvm_device_ioctl),
 };
 
 struct kvm_device *kvm_device_from_filp(struct file *filp)
@@ -3165,10 +3166,8 @@ static long kvm_vm_compat_ioctl(struct file *filp,
 static struct file_operations kvm_vm_fops = {
 	.release        = kvm_vm_release,
 	.unlocked_ioctl = kvm_vm_ioctl,
-#ifdef CONFIG_KVM_COMPAT
-	.compat_ioctl   = kvm_vm_compat_ioctl,
-#endif
 	.llseek		= noop_llseek,
+	KVM_COMPAT(kvm_vm_compat_ioctl),
 };
 
 static int kvm_dev_ioctl_create_vm(unsigned long type)
@@ -3259,8 +3258,8 @@ out:
 
 static struct file_operations kvm_chardev_ops = {
 	.unlocked_ioctl = kvm_dev_ioctl,
-	.compat_ioctl   = kvm_dev_ioctl,
 	.llseek		= noop_llseek,
+	KVM_COMPAT(kvm_dev_ioctl),
 };
 
 static struct miscdevice kvm_dev = {