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[35.247.111.240]) by smtp.gmail.com with ESMTPSA id b126sm22346155pga.91.2021.04.07.13.08.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 07 Apr 2021 13:08:46 -0700 (PDT) Date: Wed, 7 Apr 2021 20:08:42 +0000 From: Sean Christopherson To: Tom Lendacky Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, Paolo Bonzini , Jim Mattson , Joerg Roedel , Vitaly Kuznetsov , Wanpeng Li , Borislav Petkov , Ingo Molnar , Thomas Gleixner , Brijesh Singh Subject: Re: [PATCH] KVM: SVM: Make sure GHCB is mapped before updating Message-ID: References: <03b349cb19b360d4c2bbeebdd171f99298082d28.1617820214.git.thomas.lendacky@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <03b349cb19b360d4c2bbeebdd171f99298082d28.1617820214.git.thomas.lendacky@amd.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wed, Apr 07, 2021, Tom Lendacky wrote: > From: Tom Lendacky > > The sev_vcpu_deliver_sipi_vector() routine will update the GHCB to inform > the caller of the AP Reset Hold NAE event that a SIPI has been delivered. > However, if a SIPI is performed without a corresponding AP Reset Hold, > then the GHCB may not be mapped, which will result in a NULL pointer > dereference. > > Check that the GHCB is mapped before attempting the update. It's tempting to say the ghcb_set_*() helpers should guard against this, but that would add a lot of pollution and the vast majority of uses are very clearly in the vmgexit path. svm_complete_emulated_msr() is the only other case that is non-obvious; would it make sense to sanity check svm->ghcb there as well? diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index 019ac836dcd0..abe9c765628f 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -2728,7 +2728,8 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) static int svm_complete_emulated_msr(struct kvm_vcpu *vcpu, int err) { struct vcpu_svm *svm = to_svm(vcpu); - if (!sev_es_guest(vcpu->kvm) || !err) + + if (!err || !sev_es_guest(vcpu->kvm) || !WARN_ON_ONCE(svm->ghcb)) return kvm_complete_insn_gp(vcpu, err); ghcb_set_sw_exit_info_1(svm->ghcb, 1); > Fixes: 647daca25d24 ("KVM: SVM: Add support for booting APs in an SEV-ES guest") > Signed-off-by: Tom Lendacky Either way: Reviewed-by: Sean Christopherson > --- > arch/x86/kvm/svm/sev.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c > index 83e00e524513..13758e3b106d 100644 > --- a/arch/x86/kvm/svm/sev.c > +++ b/arch/x86/kvm/svm/sev.c > @@ -2105,5 +2105,6 @@ void sev_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector) > * the guest will set the CS and RIP. Set SW_EXIT_INFO_2 to a > * non-zero value. > */ > - ghcb_set_sw_exit_info_2(svm->ghcb, 1); > + if (svm->ghcb) > + ghcb_set_sw_exit_info_2(svm->ghcb, 1); > } > -- > 2.31.0 >