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From: Sean Christopherson <seanjc@google.com>
To: Eduardo Habkost <ehabkost@redhat.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>,
	Maxim Levitsky <mlevitsk@redhat.com>,
	kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	Nitesh Narayan Lal <nitesh@redhat.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 4/4] KVM: x86: Fix stack-out-of-bounds memory access from ioapic_write_indirect()
Date: Thu, 26 Aug 2021 18:01:15 +0000	[thread overview]
Message-ID: <YSfW62JxXXBI1/UE@google.com> (raw)
In-Reply-To: <20210826145210.gpfbiagntwoswrzp@habkost.net>

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 <ehabkost@redhat.com>
> ---
> 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.

  reply	other threads:[~2021-08-26 18:01 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-23 14:30 [PATCH v2 0/4] KVM: Various fixes and improvements around kicking vCPUs Vitaly Kuznetsov
2021-08-23 14:30 ` [PATCH v2 1/4] KVM: Clean up benign vcpu->cpu data races when " Vitaly Kuznetsov
2021-08-23 14:30 ` [PATCH v2 2/4] KVM: Guard cpusmask NULL check with CONFIG_CPUMASK_OFFSTACK Vitaly Kuznetsov
2021-08-23 14:30 ` [PATCH v2 3/4] KVM: Optimize kvm_make_vcpus_request_mask() a bit Vitaly Kuznetsov
2021-08-23 14:30 ` [PATCH v2 4/4] KVM: x86: Fix stack-out-of-bounds memory access from ioapic_write_indirect() Vitaly Kuznetsov
2021-08-23 18:58   ` Eduardo Habkost
2021-08-24  7:13     ` Vitaly Kuznetsov
2021-08-24 14:23       ` Eduardo Habkost
2021-08-24 14:42         ` Vitaly Kuznetsov
2021-08-24 16:07           ` Maxim Levitsky
2021-08-24 17:40             ` Sean Christopherson
2021-08-25  8:26               ` Vitaly Kuznetsov
2021-08-25  8:21             ` Vitaly Kuznetsov
2021-08-25  9:11               ` Maxim Levitsky
2021-08-25  9:43                 ` Vitaly Kuznetsov
2021-08-25 10:41                   ` Maxim Levitsky
2021-08-25 13:19                   ` Eduardo Habkost
2021-08-26 12:40                     ` Vitaly Kuznetsov
2021-08-26 14:52                       ` Eduardo Habkost
2021-08-26 18:01                         ` Sean Christopherson [this message]
2021-08-26 18:13                           ` Eduardo Habkost
2021-08-26 19:27             ` Eduardo Habkost
2021-08-30 19:47             ` Nitesh Lal

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