linux-kernel - RE: [PATCH v5 34/34] KVM: x86/vmx: execute "int $2" to handle NMI in NMI caused VM exits when FRED is enabled

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 for Android: free password hash cracker in your pocket

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

Message-ID: <SA1PR11MB6734AE9646C3018A31872D88A8879@SA1PR11MB6734.namprd11.prod.outlook.com>
Date:   Thu, 23 Mar 2023 00:26:25 +0000
From:   "Li, Xin3" <xin3.li@...el.com>
To:     "Christopherson,, Sean" <seanjc@...gle.com>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>
CC:     "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>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>
Subject: RE: [PATCH v5 34/34] KVM: x86/vmx: execute "int $2" to handle NMI in
 NMI caused VM exits when FRED is enabled

> Organization aside, this seems to defeat the purpose of _not_ unconditionally
> unmasking NMIs on ERET since the kernel assumes any random "int $2" is coming
> from KVM after an NMI VM-Exit.

I'm a bit confused.  KVM VMX is the only component needing to execute "int $2"
and it surely has NMI blocked after an NMI VM-exit.

> Eww, and "int $2" doesn't even go directly to fred_exc_nmi(), it trampolines
> through fred_sw_interrupt_kernel() first.  Looks like "int $2" from userspace gets
> routed to a #GP, so at least that bit is handled.

FRED does a 2-level dispatch, unless an event handler is on a hot path,
we don't promote its handling.  NMI seems not a frequent event.

> I'm not dead set against the proposed approach, but IMO it's not obviously better
> than a bit of assembly to have a more direct call into the NMI handler.

I will give it a shot.