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

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commit ddba91801a 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: 852b6d57dc ("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>
This commit is contained in:
Sean Christopherson 2019-02-15 12:48:39 -08:00 committed by Greg Kroah-Hartman
parent a6c42842c6
commit 9badc8549f
2 changed files with 14 additions and 5 deletions
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16
Documentation/virtual/kvm/api.txt
View File

@ -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

3
virt/kvm/kvm_main.c
View File

@ -2812,6 +2812,9 @@ 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);