linux-kernel - Re: [PATCH v2 4/5] KVM: x86: Add support for legacy VMware backdoors in nested setups

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: <aIEnm7Y1VN-PCfF8@google.com>
Date: Wed, 23 Jul 2025 11:19:07 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Zack Rusin <zack.rusin@...adcom.com>
Cc: linux-kernel@...r.kernel.org, Doug Covelli <doug.covelli@...adcom.com>, 
	Paolo Bonzini <pbonzini@...hat.com>, Jonathan Corbet <corbet@....net>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>, kvm@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v2 4/5] KVM: x86: Add support for legacy VMware backdoors
 in nested setups

On Tue, Apr 22, 2025, Zack Rusin wrote:
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index 04c375bf1ac2..74c472e51479 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -22,6 +22,7 @@
>  #include <asm/debugreg.h>
>  
>  #include "kvm_emulate.h"
> +#include "kvm_vmware.h"
>  #include "trace.h"
>  #include "mmu.h"
>  #include "x86.h"
> @@ -1517,6 +1518,11 @@ int nested_svm_exit_special(struct vcpu_svm *svm)
>  			 svm->vcpu.arch.apf.host_apf_flags)
>  			/* Trap async PF even if not shadowing */
>  			return NESTED_EXIT_HOST;
> +#ifdef CONFIG_KVM_VMWARE
> +		else if ((exit_code == (SVM_EXIT_EXCP_BASE + GP_VECTOR)) &&
> +			 kvm_vmware_wants_backdoor_to_l0(vcpu, to_svm(vcpu)->vmcb->save.cpl))
> +			return NESTED_EXIT_HOST;
> +#endif

Either provide a stub or do

		else if (IS_ENABLED(CONFIG_KVM_VMWARE) && ...)

Don't do both.  And definitely don't add a stub and #ifdef (some) callers.  I'd
say just drop the #ifdef and rely on the kvm_vmware_wants_backdoor_to_l0() stub
to get the compiler to optimize out the entire elif.

> @@ -6386,6 +6387,11 @@ static bool nested_vmx_l0_wants_exit(struct kvm_vcpu *vcpu,
>  			return true;
>  		else if (is_ve_fault(intr_info))
>  			return true;
> +#ifdef CONFIG_KVM_VMWARE
> +		else if (is_gp_fault(intr_info) &&
> +			 kvm_vmware_wants_backdoor_to_l0(vcpu, vmx_get_cpl(vcpu)))
> +			return true;
> +#endif

Same thing here.