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author | David Matlack <dmatlack@google.com> | 2022-03-03 21:33:27 +0300 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-04-08 15:40:38 +0300 |
commit | eccfee44949d2d8ac9675d5b3f29cacaed5ba6c8 (patch) | |
tree | aa8b0b45d1c2cb66f8d6c89bf5f736c5c8e43414 /virt/kvm | |
parent | 09c771c45c1243e295470225aaee726693fdc242 (diff) | |
download | linux-eccfee44949d2d8ac9675d5b3f29cacaed5ba6c8.tar.xz |
KVM: Prevent module exit until all VMs are freed
commit 5f6de5cbebee925a612856fce6f9182bb3eee0db upstream.
Tie the lifetime the KVM module to the lifetime of each VM via
kvm.users_count. This way anything that grabs a reference to the VM via
kvm_get_kvm() cannot accidentally outlive the KVM module.
Prior to this commit, the lifetime of the KVM module was tied to the
lifetime of /dev/kvm file descriptors, VM file descriptors, and vCPU
file descriptors by their respective file_operations "owner" field.
This approach is insufficient because references grabbed via
kvm_get_kvm() do not prevent closing any of the aforementioned file
descriptors.
This fixes a long standing theoretical bug in KVM that at least affects
async page faults. kvm_setup_async_pf() grabs a reference via
kvm_get_kvm(), and drops it in an asynchronous work callback. Nothing
prevents the VM file descriptor from being closed and the KVM module
from being unloaded before this callback runs.
Fixes: af585b921e5d ("KVM: Halt vcpu if page it tries to access is swapped out")
Fixes: 3d3aab1b973b ("KVM: set owner of cpu and vm file operations")
Cc: stable@vger.kernel.org
Suggested-by: Ben Gardon <bgardon@google.com>
[ Based on a patch from Ben implemented for Google's kernel. ]
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20220303183328.1499189-2-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'virt/kvm')
-rw-r--r-- | virt/kvm/kvm_main.c | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index d22de4392507..9cd8ca2d8bc1 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -114,6 +114,8 @@ EXPORT_SYMBOL_GPL(kvm_debugfs_dir); static int kvm_debugfs_num_entries; static const struct file_operations stat_fops_per_vm; +static struct file_operations kvm_chardev_ops; + static long kvm_vcpu_ioctl(struct file *file, unsigned int ioctl, unsigned long arg); #ifdef CONFIG_KVM_COMPAT @@ -818,6 +820,16 @@ static struct kvm *kvm_create_vm(unsigned long type) preempt_notifier_inc(); + /* + * When the fd passed to this ioctl() is opened it pins the module, + * but try_module_get() also prevents getting a reference if the module + * is in MODULE_STATE_GOING (e.g. if someone ran "rmmod --wait"). + */ + if (!try_module_get(kvm_chardev_ops.owner)) { + r = -ENODEV; + goto out_err; + } + return kvm; out_err: @@ -896,6 +908,7 @@ static void kvm_destroy_vm(struct kvm *kvm) preempt_notifier_dec(); hardware_disable_all(); mmdrop(mm); + module_put(kvm_chardev_ops.owner); } void kvm_get_kvm(struct kvm *kvm) |