4.4-stable review patch. If anyone has any objections, please let me know.
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From: Sean Christopherson sean.j.christopherson@intel.com
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: 852b6d57dc7f ("kvm: add device control API") Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson sean.j.christopherson@intel.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- Documentation/virtual/kvm/api.txt | 16 +++++++++++----- virt/kvm/kvm_main.c | 3 +++ 2 files changed, 14 insertions(+), 5 deletions(-)
--- a/Documentation/virtual/kvm/api.txt +++ b/Documentation/virtual/kvm/api.txt @@ -13,7 +13,7 @@ of a virtual machine. The ioctls belong
- 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 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 desc 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 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -2611,6 +2611,9 @@ static long kvm_device_ioctl(struct file { 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);