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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id u25sm3503724pfn.209.2021.08.26.11.01.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Aug 2021 11:01:19 -0700 (PDT) Date: Thu, 26 Aug 2021 18:01:15 +0000 From: Sean Christopherson To: Eduardo Habkost Cc: Vitaly Kuznetsov , Maxim Levitsky , kvm@vger.kernel.org, Paolo Bonzini , Wanpeng Li , Jim Mattson , "Dr. David Alan Gilbert" , Nitesh Narayan Lal , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 4/4] KVM: x86: Fix stack-out-of-bounds memory access from ioapic_write_indirect() Message-ID: References: <87mtp7jowv.fsf@vitty.brq.redhat.com> <87k0kakip9.fsf@vitty.brq.redhat.com> <2df0b6d18115fb7f2701587b7937d8ddae38e36a.camel@redhat.com> <87h7fej5ov.fsf@vitty.brq.redhat.com> <36b6656637d1e6aaa2ab5098f7ebc27644466294.camel@redhat.com> <87bl5lkgfm.fsf@vitty.brq.redhat.com> <87tujcidka.fsf@vitty.brq.redhat.com> <20210826145210.gpfbiagntwoswrzp@habkost.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210826145210.gpfbiagntwoswrzp@habkost.net> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 26, 2021, Eduardo Habkost wrote: > > @@ -918,7 +918,7 @@ static bool kvm_apic_is_broadcast_dest(struct kvm *kvm, struct kvm_lapic **src, > > static inline bool kvm_apic_map_get_dest_lapic(struct kvm *kvm, > > struct kvm_lapic **src, struct kvm_lapic_irq *irq, > > struct kvm_apic_map *map, struct kvm_lapic ***dst, > > - unsigned long *bitmap) > > + unsigned long *bitmap64) > > You can communicate the expected bitmap size to the compiler > without typedefs if using DECLARE_BITMAP inside the function > parameter list is acceptable coding style (is it?). > > For example, the following would have allowed the compiler to > catch the bug you are fixing: > > Signed-off-by: Eduardo Habkost > --- > diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h > index d7c25d0c1354..e8c64747121a 100644 > --- a/arch/x86/kvm/lapic.h > +++ b/arch/x86/kvm/lapic.h > @@ -236,7 +236,7 @@ bool kvm_apic_pending_eoi(struct kvm_vcpu *vcpu, int vector); > void kvm_wait_lapic_expire(struct kvm_vcpu *vcpu); > > void kvm_bitmap_or_dest_vcpus(struct kvm *kvm, struct kvm_lapic_irq *irq, > - unsigned long *vcpu_bitmap); > + DECLARE_BITMAP(vcpu_bitmap, KVM_MAX_VCPUS)); > > bool kvm_intr_is_single_vcpu_fast(struct kvm *kvm, struct kvm_lapic_irq *irq, > struct kvm_vcpu **dest_vcpu); > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index 76fb00921203..1df113894cba 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -1166,7 +1166,7 @@ static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode, > * each available vcpu to identify the same. > */ > void kvm_bitmap_or_dest_vcpus(struct kvm *kvm, struct kvm_lapic_irq *irq, > - unsigned long *vcpu_bitmap) > + DECLARE_BITMAP(vcpu_bitmap, KVM_MAX_VCPUS)) > { > struct kvm_lapic **dest_vcpu = NULL; > struct kvm_lapic *src = NULL; Sadly, that would not have actually caught the bug. In C++, an array param does indeed have a fixed size, but in C an array param is nothing more than syntatic sugar that is demoted to a plain ol' pointer. E.g. gcc-10 and clang-11 both happily compile with "DECLARE_BITMAP(vcpu_bitmap, 0)" and the original single "unsigned long vcpu_bitmap". Maybe there are gcc extensions to enforce array sizes? But if there are, they are not (yet) enabled for kernel builds.