KVM: Add a comment describing the /dev/kvm no_compat handling

Add a comment explaining the rational behind having both no_compat open and ioctl callbacks to fend off compat tasks. Signed-off-by: Marc Zyngier <[email protected]> Signed-off-by: Paolo Bonzini <[email protected]>
vieko · Nov 15, 2019 · 9cb09e7 · 9cb09e7
1 parent ed69a6c
commit 9cb09e7
Showing 1 changed file with 7 additions and 0 deletions.
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
@@ -122,6 +122,13 @@ static long kvm_vcpu_compat_ioctl(struct file *file, unsigned int ioctl,
 				  unsigned long arg);
 #define KVM_COMPAT(c)	.compat_ioctl	= (c)
 #else
+/*
+ * For architectures that don't implement a compat infrastructure,
+ * adopt a double line of defense:
+ * - Prevent a compat task from opening /dev/kvm
+ * - If the open has been done by a 64bit task, and the KVM fd
+ *   passed to a compat task, let the ioctls fail.
+ */
 static long kvm_no_compat_ioctl(struct file *file, unsigned int ioctl,
 				unsigned long arg) { return -EINVAL; }