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Commit 7ceedcef authored by Sean Christopherson's avatar Sean Christopherson Committed by Greg Kroah-Hartman
Browse files

KVM: Reject device ioctls from processes other than the VM's creator 



commit ddba91801aeb5c160b660caed1800eb3aef403f8 upstream.

KVM's API requires thats ioctls must be issued from the same process
that created the VM.  In other words, userspace can play games with a
VM's file descriptors, e.g. fork(), SCM_RIGHTS, etc..., but only the
creator can do anything useful.  Explicitly reject device ioctls that
are issued by a process other than the VM's creator, and update KVM's
API documentation to extend its requirements to device ioctls.

Fixes: 852b6d57 ("kvm: add device control API")
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent a0713e81

Documentation/virtual/kvm/api.txt

+11 −5
Original line number Diff line number Diff line
@@ -13,7 +13,7 @@ of a virtual machine. The ioctls belong to three classes 


 - VM ioctls: These query and set attributes that affect an entire virtual

   machine, for example memory layout.  In addition a VM ioctl is used to

   create virtual cpus (vcpus).

   create virtual cpus (vcpus) and devices.



   Only run VM ioctls from the same process (address space) that was used

   to create the VM.
@@ -24,6 +24,11 @@ of a virtual machine. The ioctls belong to three classes 
   Only run vcpu ioctls from the same thread that was used to create the

   vcpu.



 - device ioctls: These query and set attributes that control the operation

   of a single device.



   device ioctls must be issued from the same process (address space) that

   was used to create the VM.



2. File descriptors

-------------------
@@ -32,10 +37,11 @@ The kvm API is centered around file descriptors. An initial 
open("/dev/kvm") obtains a handle to the kvm subsystem; this handle

can be used to issue system ioctls.  A KVM_CREATE_VM ioctl on this

handle will create a VM file descriptor which can be used to issue VM

ioctls.  A KVM_CREATE_VCPU ioctl on a VM fd will create a virtual cpu

and return a file descriptor pointing to it.  Finally, ioctls on a vcpu

fd can be used to control the vcpu, including the important task of

actually running guest code.

ioctls.  A KVM_CREATE_VCPU or KVM_CREATE_DEVICE ioctl on a VM fd will

create a virtual cpu or device and return a file descriptor pointing to

the new resource.  Finally, ioctls on a vcpu or device fd can be used

to control the vcpu or device.  For vcpus, this includes the important

task of actually running guest code.



In general file descriptors can be migrated among processes by means

of fork() and the SCM_RIGHTS facility of unix domain socket.  These

virt/kvm/kvm_main.c

+3 −0
Original line number Diff line number Diff line
@@ -2815,6 +2815,9 @@ static long kvm_device_ioctl(struct file *filp, unsigned int ioctl, 
{

	struct kvm_device *dev = filp->private_data;



	if (dev->kvm->mm != current->mm)

		return -EIO;



	switch (ioctl) {

	case KVM_SET_DEVICE_ATTR:

		return kvm_device_ioctl_attr(dev, dev->ops->set_attr, arg);