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@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 63d04348371b ("KVM: x86: move kvm_create_vcpu_debugfs after last failure point")
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
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 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
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
}
--
2.26.2
