Re: [PATCH v2 2/5] x86/tdx: Add validation of userspace MMIO instructions

[Edgecombe, Rick P]

On Mon, 2024-08-05 at 15:29 +0200, Alexey Gladkov (Intel) wrote:
> +       vaddr = (unsigned long)insn_get_addr_ref(&insn, regs);
> +
> +       if (user_mode(regs)) {
> +               if (mmap_read_lock_killable(current->mm))
> +                       return -EINTR;
> +
> +               ret = valid_vaddr(ve, mmio, size, vaddr);
> +               if (ret)
> +                       goto unlock;
> +       }
> +

In the case of user MMIO, if the user instruction + MAX_INSN_SIZE straddles a
page, then the "fetch" in the kernel could trigger a #VE. In this case the  
kernel would handle this second #VE as a !user_mode() MMIO I guess.

Would something prevent the same munmap() checks needing to happen for that
second kernel #VE? If not, I wonder if the munmap() protection logic should also
trigger for any userspace range ve->gpa as well.