From d56f5136b01020155b6b0a29f69d924687529bee Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Thu, 4 Jun 2020 15:16:52 +0200 Subject: [PATCH] KVM: let kvm_destroy_vm_debugfs clean up vCPU debugfs directories After commit 63d0434 ("KVM: x86: move kvm_create_vcpu_debugfs after last failure point") we are creating the pre-vCPU debugfs files after the creation of the vCPU file descriptor. This makes it possible for userspace to reach kvm_vcpu_release before kvm_create_vcpu_debugfs has finished. The vcpu->debugfs_dentry then does not have any associated inode anymore, and this causes a NULL-pointer dereference in debugfs_create_file. The solution is simply to avoid removing the files; they are cleaned up when the VM file descriptor is closed (and that must be after KVM_CREATE_VCPU returns). We can stop storing the dentry in struct kvm_vcpu too, because it is not needed anywhere after kvm_create_vcpu_debugfs returns. Reported-by: syzbot+705f4401d5a93a59b87d@syzkaller.appspotmail.com Fixes: 63d04348371b ("KVM: x86: move kvm_create_vcpu_debugfs after last failure point") Signed-off-by: Paolo Bonzini --- arch/arm64/kvm/arm.c | 5 ----- arch/x86/kvm/debugfs.c | 10 +++++----- include/linux/kvm_host.h | 3 +-- virt/kvm/kvm_main.c | 8 ++++---- 4 files changed, 10 insertions(+), 16 deletions(-) diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index 7a57381c05e8..45276ed50dd6 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -144,11 +144,6 @@ out_fail_alloc: return ret; } -int kvm_arch_create_vcpu_debugfs(struct kvm_vcpu *vcpu) -{ - return 0; -} - vm_fault_t kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf) { return VM_FAULT_SIGBUS; diff --git a/arch/x86/kvm/debugfs.c b/arch/x86/kvm/debugfs.c index 018aebce33ff..7e818d64bb4d 100644 --- a/arch/x86/kvm/debugfs.c +++ b/arch/x86/kvm/debugfs.c @@ -43,22 +43,22 @@ static int vcpu_get_tsc_scaling_frac_bits(void *data, u64 *val) DEFINE_SIMPLE_ATTRIBUTE(vcpu_tsc_scaling_frac_fops, vcpu_get_tsc_scaling_frac_bits, NULL, "%llu\n"); -void kvm_arch_create_vcpu_debugfs(struct kvm_vcpu *vcpu) +void kvm_arch_create_vcpu_debugfs(struct kvm_vcpu *vcpu, struct dentry *debugfs_dentry) { - debugfs_create_file("tsc-offset", 0444, vcpu->debugfs_dentry, vcpu, + debugfs_create_file("tsc-offset", 0444, debugfs_dentry, vcpu, &vcpu_tsc_offset_fops); if (lapic_in_kernel(vcpu)) debugfs_create_file("lapic_timer_advance_ns", 0444, - vcpu->debugfs_dentry, vcpu, + debugfs_dentry, vcpu, &vcpu_timer_advance_ns_fops); if (kvm_has_tsc_control) { debugfs_create_file("tsc-scaling-ratio", 0444, - vcpu->debugfs_dentry, vcpu, + debugfs_dentry, vcpu, &vcpu_tsc_scaling_fops); debugfs_create_file("tsc-scaling-ratio-frac-bits", 0444, - vcpu->debugfs_dentry, vcpu, + debugfs_dentry, vcpu, &vcpu_tsc_scaling_frac_fops); } } diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index f43b59b1294c..d38d6b9c24be 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -318,7 +318,6 @@ struct kvm_vcpu { bool preempted; bool ready; struct kvm_vcpu_arch arch; - struct dentry *debugfs_dentry; }; static inline int kvm_vcpu_exiting_guest_mode(struct kvm_vcpu *vcpu) @@ -888,7 +887,7 @@ void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu); void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu); #ifdef __KVM_HAVE_ARCH_VCPU_DEBUGFS -void kvm_arch_create_vcpu_debugfs(struct kvm_vcpu *vcpu); +void kvm_arch_create_vcpu_debugfs(struct kvm_vcpu *vcpu, struct dentry *debugfs_dentry); #endif int kvm_arch_hardware_enable(void); diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 7fa1e38e1659..3577eb84eac0 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -2973,7 +2973,6 @@ static int kvm_vcpu_release(struct inode *inode, struct file *filp) { struct kvm_vcpu *vcpu = filp->private_data; - debugfs_remove_recursive(vcpu->debugfs_dentry); kvm_put_kvm(vcpu->kvm); return 0; } @@ -3000,16 +2999,17 @@ static int create_vcpu_fd(struct kvm_vcpu *vcpu) static void kvm_create_vcpu_debugfs(struct kvm_vcpu *vcpu) { #ifdef __KVM_HAVE_ARCH_VCPU_DEBUGFS + struct dentry *debugfs_dentry; char dir_name[ITOA_MAX_LEN * 2]; if (!debugfs_initialized()) return; snprintf(dir_name, sizeof(dir_name), "vcpu%d", vcpu->vcpu_id); - vcpu->debugfs_dentry = debugfs_create_dir(dir_name, - vcpu->kvm->debugfs_dentry); + debugfs_dentry = debugfs_create_dir(dir_name, + vcpu->kvm->debugfs_dentry); - kvm_arch_create_vcpu_debugfs(vcpu); + kvm_arch_create_vcpu_debugfs(vcpu, debugfs_dentry); #endif }