From 8dcf70ab1830a98807089f592cc4bd89cda50083 Mon Sep 17 00:00:00 2001 From: Paul Mackerras Date: Tue, 12 Sep 2017 15:42:38 +1000 Subject: [PATCH] KVM: PPC: Book3S HV: Protect updates to spapr_tce_tables list commit edd03602d97236e8fea13cd76886c576186aa307 upstream. Al Viro pointed out that while one thread of a process is executing in kvm_vm_ioctl_create_spapr_tce(), another thread could guess the file descriptor returned by anon_inode_getfd() and close() it before the first thread has added it to the kvm->arch.spapr_tce_tables list. That highlights a more general problem: there is no mutual exclusion between writers to the spapr_tce_tables list, leading to the possibility of the list becoming corrupted, which could cause a host kernel crash. To fix the mutual exclusion problem, we add a mutex_lock/unlock pair around the list_del_rce in kvm_spapr_tce_release(). If another thread does guess the file descriptor returned by the anon_inode_getfd() call in kvm_vm_ioctl_create_spapr_tce() and closes it, its call to kvm_spapr_tce_release() will not do any harm because it will have to wait until the first thread has released kvm->lock. The other things that the second thread could do with the guessed file descriptor are to mmap it or to pass it as a parameter to a KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE ioctl on a KVM device fd. An mmap call won't cause any harm because kvm_spapr_tce_mmap() and kvm_spapr_tce_fault() don't access the spapr_tce_tables list or the kvmppc_spapr_tce_table.list field, and the fields that they do use have been properly initialized by the time of the anon_inode_getfd() call. The KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE ioctl calls kvm_spapr_tce_attach_iommu_group(), which scans the spapr_tce_tables list looking for the kvmppc_spapr_tce_table struct corresponding to the fd given as the parameter. Either it will find the new entry or it won't; if it doesn't, it just returns an error, and if it does, it will function normally. So, in each case there is no harmful effect. [paulus@ozlabs.org - moved parts of the upstream patch into the backport of 47c5310a8dbe, adjusted this commit message accordingly.] Fixes: 366baf28ee3f ("KVM: PPC: Use RCU for arch.spapr_tce_tables") Reviewed-by: David Gibson Signed-off-by: Paul Mackerras Signed-off-by: Greg Kroah-Hartman --- arch/powerpc/kvm/book3s_64_vio.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c index 7c1cb9d..da2a7ec 100644 --- a/arch/powerpc/kvm/book3s_64_vio.c +++ b/arch/powerpc/kvm/book3s_64_vio.c @@ -129,8 +129,11 @@ static int kvm_spapr_tce_mmap(struct file *file, struct vm_area_struct *vma) static int kvm_spapr_tce_release(struct inode *inode, struct file *filp) { struct kvmppc_spapr_tce_table *stt = filp->private_data; + struct kvm *kvm = stt->kvm; + mutex_lock(&kvm->lock); list_del_rcu(&stt->list); + mutex_unlock(&kvm->lock); kvm_put_kvm(stt->kvm); -- 2.7.4