linux-kernel - RE: [RESEND PATCH 5/6] KVM: x86/VMX: add kvm_vmx_reinject_nmi

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]

Date:   Tue, 15 Nov 2022 07:50:49 +0000
From:   "Li, Xin3" <xin3.li@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Paolo Bonzini <pbonzini@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "Tian, Kevin" <kevin.tian@...el.com>
Subject: RE: [RESEND PATCH 5/6] KVM: x86/VMX: add kvm_vmx_reinject_nmi_irq()
 for NMI/IRQ reinjection

> > > But what about NMIs, afaict this is all horribly broken for NMIs.
> > >
> > > So the whole VMX thing latches the NMI (which stops NMI recursion),
> right?
> > >
> > > But then you drop out of noinstr code, which means any random
> > > exception can happen (kprobes #BP, hw_breakpoint #DB, or even #PF
> > > due to random nonsense like *SAN). This exception will do IRET and
> > > clear the NMI latch, all before you get to run any of the NMI code.
> >
> > What you said here implies that we have this problem in the existing code.
> > Because a fake iret stack is created to call the NMI handler in the
> > IDT NMI descriptor, which lastly executes the IRET instruction.
> 
> I can't follow; of course the IDT handler terminates with IRET, it has to no?

With FRED, ERETS/ERETU replace IRET, and use bit 28 of the popped CS field
to control whether to unblock NMI. If bit 28 of the field (above the selector)
is 1, ERETS/ERETU unblocks NMIs.

> 
> And yes, the current code appears to suffer the same defect.