Can't boot after update

[csete]

I'm running 18.04 on my Dell XPS 15 9570, in dual boot mode with Windows 10. I have not disabled secure boot, because it all seemed to be working well. Last night I ran software updater and I can no longer boot the machine. I'm seeing:

error: /boot/vmlinuz-5.0.0-21-generic has invalid signature.
error: you need to load the kernel first

Poking around the net for similar errors, this appears to be related to secure boot. Is there any way to get my machine back up and running without turning off secure boot?

Thanks,
Craig

[prafulladv]

I am getting the Invalid signature error when I updated to Ubuntu 18.04. Before update, I had Windows 10 home and Kali Linux. Now while booting Kali , I get this error. Windows is booting fine.
I don't want to change secure boot settings

error: /boot/vmlinuz-4.15.0-kali2-amd64 has invalid signature
error: you need to load the kernel first.

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