linux-kernel - Re: [PATCH v16 29/51] KVM: VMX: Configure nested capabilities after CPU capabilities

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: <aNLJosN_1gZ7z4VF@google.com>
Date: Tue, 23 Sep 2025 09:24:02 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Chao Gao <chao.gao@...el.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Tom Lendacky <thomas.lendacky@....com>, Mathias Krause <minipli@...ecurity.net>, 
	John Allen <john.allen@....com>, Rick Edgecombe <rick.p.edgecombe@...el.com>, 
	Binbin Wu <binbin.wu@...ux.intel.com>, Xiaoyao Li <xiaoyao.li@...el.com>, 
	Maxim Levitsky <mlevitsk@...hat.com>, Zhang Yi Z <yi.z.zhang@...ux.intel.com>, Xin Li <xin@...or.com>
Subject: Re: [PATCH v16 29/51] KVM: VMX: Configure nested capabilities after
 CPU capabilities

On Tue, Sep 23, 2025, Chao Gao wrote:
> On Fri, Sep 19, 2025 at 03:32:36PM -0700, Sean Christopherson wrote:
> >Swap the order between configuring nested VMX capabilities and base CPU
> >capabilities, so that nested VMX support can be conditioned on core KVM
> >support, e.g. to allow conditioning support for LOAD_CET_STATE on the
> >presence of IBT or SHSTK.  Because the sanity checks on nested VMX config
> >performed by vmx_check_processor_compat() run _after_ vmx_hardware_setup(),
> >any use of kvm_cpu_cap_has() when configuring nested VMX support will lead
> >to failures in vmx_check_processor_compat().
> >
> >While swapping the order of two (or more) configuration flows can lead to
> >a game of whack-a-mole, in this case nested support inarguably should be
> >done after base support.  KVM should never condition base support on nested
> >support, because nested support is fully optional, while obviously it's
> >desirable to condition nested support on base support.  And there's zero
> >evidence the current ordering was intentional, e.g. commit 66a6950f9995
> >("KVM: x86: Introduce kvm_cpu_caps to replace runtime CPUID masking")
> >likely placed the call to kvm_set_cpu_caps() after nested setup because it
> >looked pretty.
> >
> >Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> 
> Reviewed-by: Chao Gao <chao.gao@...el.com>
> 
> I had a feeling I'd seen this patch before :). After some searching in lore, I
> tracked it down:
> https://lore.kernel.org/kvm/20241001050110.3643764-22-xin@zytor.com/

Gah, sorry Xin :-/