On Mon, Sep 13 2021 at 13:01, Sohil Mehta wrote:
> +/*
> + * No lock is needed to read the active flag. Writes only happen from
> + * r_info->task that owns the UPID. Everyone else would just read this flag.
> + *
> + * This only provides a static check. The receiver may become inactive right
> + * after this check. The primary reason to have this check is to prevent future
> + * senders from connecting with this UPID, since the receiver task has already
> + * made this UPID inactive.
How is that not racy?
> +static void free_uitt(struct uintr_uitt_ctx *uitt_ctx)
> +{
> + unsigned long flags;
> +
> + spin_lock_irqsave(&uitt_ctx->uitt_lock, flags);
> + kfree(uitt_ctx->uitt);
Again. Please move kfree() outside of the lock held region. But aside of
that what is this lock protecting here?
> + uitt_ctx->uitt = NULL;
> + spin_unlock_irqrestore(&uitt_ctx->uitt_lock, flags);
If there is concurrency then the other task which is blocked on
uitt_lock will operate on uitt_ctx while the same is freed.
Again, this lacks any life time and serialization rules. Just sprinkling
locks all over the place does not make it magically correct.
> + kfree(uitt_ctx);
> +}
> +static void put_uitt_ref(struct uintr_uitt_ctx *uitt_ctx)
> +{
> + if (refcount_dec_and_test(&uitt_ctx->refs))
> + free_uitt(uitt_ctx);
> +}
> +static struct uintr_uitt_ctx *get_uitt_ref(struct uintr_uitt_ctx *uitt_ctx)
> +{
> + refcount_inc(&uitt_ctx->refs);
> + return uitt_ctx;
> +}
> +
> +static inline void mark_uitte_invalid(struct uintr_sender_info *s_info)
> +{
> + struct uintr_uitt_entry *uitte;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&s_info->uitt_ctx->uitt_lock, flags);
> + uitte = &s_info->uitt_ctx->uitt[s_info->uitt_index];
> + uitte->valid = 0;
> + spin_unlock_irqrestore(&s_info->uitt_ctx->uitt_lock, flags);
> +}
> +
> static void __clear_vector_from_upid(u64 uvec, struct uintr_upid *upid)
> {
> clear_bit(uvec, (unsigned long *)&upid->puir);
> @@ -175,6 +290,210 @@ static void receiver_clear_uvec(struct callback_head *head)
> kfree(r_info);
> }
>
> +static void teardown_uitt(void)
> +{
> + struct task_struct *t = current;
> + struct fpu *fpu = &t->thread.fpu;
> + u64 msr64;
> +
> + put_uitt_ref(t->thread.ui_send->uitt_ctx);
> + kfree(t->thread.ui_send);
> + t->thread.ui_send = NULL;
> +
> + fpregs_lock();
> +
> + if (fpregs_state_valid(fpu, smp_processor_id())) {
> + /* Modify only the relevant bits of the MISC MSR */
> + rdmsrl(MSR_IA32_UINTR_MISC, msr64);
> + msr64 &= GENMASK_ULL(63, 32);
More magic numbers.
> + wrmsrl(MSR_IA32_UINTR_MISC, msr64);
> + wrmsrl(MSR_IA32_UINTR_TT, 0ULL);
> +static void __free_uitt_entry(unsigned int entry)
> +{
> + struct task_struct *t = current;
> + unsigned long flags;
> +
> + if (entry >= UINTR_MAX_UITT_NR)
> + return;
> +
> + if (!is_uintr_sender(t))
> + return;
> +
> + pr_debug("send: Freeing UITTE entry %d for task=%d\n", entry, t->pid);
> +
> + spin_lock_irqsave(&t->thread.ui_send->uitt_ctx->uitt_lock, flags);
> + memset(&t->thread.ui_send->uitt_ctx->uitt[entry], 0,
> + sizeof(struct uintr_uitt_entry));
> + spin_unlock_irqrestore(&t->thread.ui_send->uitt_ctx->uitt_lock,
> flags);
What's the spinlock protecting here?
> + clear_bit(entry, (unsigned long *)t->thread.ui_send->uitt_mask);
> +
> + if (is_uitt_empty(t)) {
> + pr_debug("send: UITT mask is empty. Dereference and teardown UITT\n");
> + teardown_uitt();
> + }
> +}
> +void do_uintr_unregister_sender(struct uintr_receiver_info *r_info,
> + struct uintr_sender_info *s_info)
> +{
> + int ret;
> +
> + /*
> + * To make sure any new senduipi result in a #GP fault.
> + * The task work might take non-zero time to kick the process out.
-ENOPARSE
> + */
> + mark_uitte_invalid(s_info);
> +
> + pr_debug("send: Adding Free UITTE %d task work for task=%d\n",
> + s_info->uitt_index, s_info->task->pid);
> +
> + init_task_work(&s_info->twork, sender_free_uitte);
> + ret = task_work_add(s_info->task, &s_info->twork, true);
> + if (ret) {
> + /*
> + * Dereferencing the UITT and UPID here since the task has
> + * exited.
> + */
> + pr_debug("send: Free UITTE %d task=%d has already exited\n",
> + s_info->uitt_index, s_info->task->pid);
> + put_upid_ref(s_info->r_upid_ctx);
> + put_uitt_ref(s_info->uitt_ctx);
> + put_task_struct(s_info->task);
> + kfree(s_info);
> + return;
> + }
> +}
> +
> +int do_uintr_register_sender(struct uintr_receiver_info *r_info,
> + struct uintr_sender_info *s_info)
> +{
> + struct uintr_uitt_entry *uitte = NULL;
> + struct uintr_sender *ui_send;
> + struct task_struct *t = current;
> + unsigned long flags;
> + int entry;
> + int ret;
> +
> + /*
> + * Only a static check. Receiver could exit anytime after this check.
> + * This check only prevents connections using uintr_fd after the
> + * receiver has already exited/unregistered.
> + */
> + if (!uintr_is_receiver_active(r_info))
> + return -ESHUTDOWN;
How is this safe against a concurrent unregister/exit operation?
Thanks,
tglx
