Re: [PATCH 0/5] kvm: fix latent guest entry/exit bugs

[Paolo Bonzini]

On 1/14/22 16:19, Mark Rutland wrote:
> I also think there is another issue here. When an IRQ is taken from SIE, will
> user_mode(regs) always be false, or could it be true if the guest userspace is
> running? If it can be true I think tha context tracking checks can complain,
> and it*might*  be possible to trigger a panic().

I think that it would be false, because the guest PSW is in the SIE 
block and switched on SIE entry and exit, but I might be incorrect.

Paolo

> In irqentry_enter(), if user_mode(regs) == true, we call
> irqentry_enter_from_user_mode -> __enter_from_user_mode(). There we check that
> the context is CONTEXT_USER, but IIUC that will be CONTEXT_GUEST at this point.
> We also call arch_check_user_regs(), and IIUC this might permit a malicious
> guest to trigger a host panic by way of debug_user_asce(), but I may have
> misunderstood and that might not be possible.