linux-kernel - Re: [PATCH v2 2/9] KVM: x86: remove return value of kvm_vcpu

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <YykMc2NDOzvG+xoy@google.com>
Date:   Tue, 20 Sep 2022 00:42:27 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        mlevitsk@...hat.com, vkuznets@...hat.com
Subject: Re: [PATCH v2 2/9] KVM: x86: remove return value of kvm_vcpu_block

On Wed, Aug 17, 2022, Sean Christopherson wrote:
> Side topic, usage of kvm_apic_accept_events() appears to be broken (though nothing
> can trigger the bug).  If kvm_apic_accept_events() were to return an -errno, then
> kvm_arch_vcpu_ioctl_run() would return '0' to userspace without updating
> vcpu->run->exit_reason.  I think an easy fix is to drop the return value entirely
> and then WARN if kvm_check_nested_events() returns something other than -EBUSY.
> 
> 	if (is_guest_mode(vcpu)) {
> 		r = kvm_check_nested_events(vcpu);
> 		if (r < 0) {
> 			WARN_ON_ONCE(r != -EBUSY);
> 			return;
> 		}

For posterity, I was wrong.  Way down the stack, vmx_complete_nested_posted_interrupt()
can return -ENXIO after filling vcpu->run->exit_reason via kvm_handle_memory_failure().
That's the entire reason why negative values from kvm_check_nested_events() and
kvm_apic_accept_events() are morphed to '0', i.e. to "exit to userspace".