linux-kernel - Re: [PATCH 3/3] KVM: SVM: allow to intercept all exceptions for debug

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: <YFBtI55sVzIJ15U+@8bytes.org>
Date:   Tue, 16 Mar 2021 09:32:35 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Maxim Levitsky <mlevitsk@...hat.com>
Cc:     kvm@...r.kernel.org, Vitaly Kuznetsov <vkuznets@...hat.com>,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Wanpeng Li <wanpengli@...cent.com>,
        Kieran Bingham <kbingham@...nel.org>,
        Jessica Yu <jeyu@...nel.org>,
        Jan Kiszka <jan.kiszka@...mens.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Borislav Petkov <bp@...en8.de>,
        Stefano Garzarella <sgarzare@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH 3/3] KVM: SVM: allow to intercept all exceptions for debug

Hi Maxim,

On Tue, Mar 16, 2021 at 12:10:20AM +0200, Maxim Levitsky wrote:
> -static int (*const svm_exit_handlers[])(struct kvm_vcpu *vcpu) = {
> +static int (*svm_exit_handlers[])(struct kvm_vcpu *vcpu) = {

Can you keep this const and always set the necessary handlers? If
exceptions are not intercepted they will not be used.

> @@ -333,7 +334,9 @@ static inline void clr_exception_intercept(struct vcpu_svm *svm, u32 bit)
>  	struct vmcb *vmcb = svm->vmcb01.ptr;
>  
>  	WARN_ON_ONCE(bit >= 32);
> -	vmcb_clr_intercept(&vmcb->control, INTERCEPT_EXCEPTION_OFFSET + bit);
> +
> +	if (!((1 << bit) & debug_intercept_exceptions))
> +		vmcb_clr_intercept(&vmcb->control, INTERCEPT_EXCEPTION_OFFSET + bit);

This will break SEV-ES guests, as those will not cause an intercept but
now start to get #VC exceptions on every other exception that is raised.
SEV-ES guests are not prepared for that and will not even boot, so
please don't enable this feature for them.