riscv: bhyve: add NULL check for hyp in riscv_send_ipi

[doonbsd_gmail.com]

Summary

In riscv_send_ipi(), check if hyp is NULL before accessing hyp->vm
to prevent a potential NULL pointer dereference.

Micro-optimization: Use __predict_false for the hypctx == NULL check.

Signed-off-by: Doongar Singh <[e-mail]>

[jrtc27]

Commit message does not say the "why", only the "what"; i.e. it doesn't say under what circumstances this can happen. Can it happen? It would seem like a rather broken state to be in.

[doonbsd_gmail.com]

riscv_send_ipi() is an independent non-static helper function. Since the check is for all possible CPUs and not just active CPUs, any part of the kernel (malicious) can call it with wrong arguments and cause a kernel panic. I think its a good defensive check.

[jrtc27]

That is not in general sufficient reasoning

[doonbsd_gmail.com]

I am sorry. Being defensive when function is open for abuse is not good enough? Also, the guest SBI calls can't be trusted.