linux-kernel - Re: [patch v2] x86: kvm: x86: fix information leak to userland

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Date:	Tue, 26 Jul 2011 19:05:00 +0200
From:	Alexander Graf <agraf@...e.de>
To:	Vasiliy Kulikov <segooon@...il.com>
Cc:	Jan Kiszka <jan.kiszka@....de>, kernel-janitors@...r.kernel.org,
	Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch v2] x86: kvm: x86: fix information leak to userland


On 30.10.2010, at 20:54, Vasiliy Kulikov wrote:

> Structures kvm_vcpu_events, kvm_debugregs, kvm_pit_state2 and
> kvm_clock_data are copied to userland with some padding and reserved
> fields unitialized.  It leads to leaking of contents of kernel stack
> memory.  We have to initialize them to zero.
> 
> In patch v1 Jan Kiszka suggested to fill reserved fields with zeros
> instead of memset'ting the whole struct.  It makes sense as these
> fields are explicitly marked as padding.  No more fields need zeroing.
> 
> Signed-off-by: Vasiliy Kulikov <segooon@...il.com>
> ---
> Compile tesed only.
> 
> arch/x86/kvm/x86.c |    6 ++++++
> 1 files changed, 6 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b0818f6..463c65b 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2560,6 +2560,7 @@ static void kvm_vcpu_ioctl_x86_get_vcpu_events(struct kvm_vcpu *vcpu,
> 		!kvm_exception_is_soft(vcpu->arch.exception.nr);
> 	events->exception.nr = vcpu->arch.exception.nr;
> 	events->exception.has_error_code = vcpu->arch.exception.has_error_code;
> +	events->exception.pad = 0;
> 	events->exception.error_code = vcpu->arch.exception.error_code;
> 
> 	events->interrupt.injected =
> @@ -2573,12 +2574,14 @@ static void kvm_vcpu_ioctl_x86_get_vcpu_events(struct kvm_vcpu *vcpu,
> 	events->nmi.injected = vcpu->arch.nmi_injected;
> 	events->nmi.pending = vcpu->arch.nmi_pending;
> 	events->nmi.masked = kvm_x86_ops->get_nmi_mask(vcpu);
> +	events->nmi.pad = 0;
> 
> 	events->sipi_vector = vcpu->arch.sipi_vector;
> 
> 	events->flags = (KVM_VCPUEVENT_VALID_NMI_PENDING
> 			 | KVM_VCPUEVENT_VALID_SIPI_VECTOR
> 			 | KVM_VCPUEVENT_VALID_SHADOW);
> +	memset(&events->reserved, 0, sizeof(events->reserved));
> }
> 
> static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
> @@ -2623,6 +2626,7 @@ static void kvm_vcpu_ioctl_x86_get_debugregs(struct kvm_vcpu *vcpu,
> 	dbgregs->dr6 = vcpu->arch.dr6;
> 	dbgregs->dr7 = vcpu->arch.dr7;
> 	dbgregs->flags = 0;
> +	memset(&dbgregs->reserved, 0, sizeof(dbgregs->reserved));
> }
> 
> static int kvm_vcpu_ioctl_x86_set_debugregs(struct kvm_vcpu *vcpu,
> @@ -3106,6 +3110,7 @@ static int kvm_vm_ioctl_get_pit2(struct kvm *kvm, struct kvm_pit_state2 *ps)
> 		sizeof(ps->channels));
> 	ps->flags = kvm->arch.vpit->pit_state.flags;
> 	mutex_unlock(&kvm->arch.vpit->pit_state.lock);
> +	memset(&ps->reserved, 0, sizeof(ps->reserved));

struct kvm_pit_state2 {
        struct kvm_pit_channel_state channels[3];
        __u32 flags;
        __u32 reserved[9];
};

So memset(&ps->reserved) would give you the a __u32 **, no? Same goes for all the other array sets in here. Or am I understanding some C logic wrong? :)


Alex

> 	return r;
> }
> 
> @@ -3486,6 +3491,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
> 		user_ns.clock = kvm->arch.kvmclock_offset + now_ns;
> 		local_irq_enable();
> 		user_ns.flags = 0;
> +		memset(&user_ns.pad, 0, sizeof(user_ns.pad));
> 
> 		r = -EFAULT;
> 		if (copy_to_user(argp, &user_ns, sizeof(user_ns)))
> -- 
> Vasiliy
> --
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