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

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Date:	Tue, 26 Jul 2011 19:39:16 +0200
From:	Alexander Graf <agraf@...e.de>
To:	Vasiliy Kulikov <segoon@...nwall.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 26.07.2011, at 19:28, Vasiliy Kulikov wrote:

> Alexander,
> 
> On Tue, Jul 26, 2011 at 19:05 +0200, Alexander Graf wrote:
>>> @@ -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? :)
> 
> No, the array name and an address of the array give the same address.  I
> could use ps->reserved instead of &ps->reserved, but it is a question of
> coding style.  I got opposite opinions on this question from different
> maintainers.
> 
> Another thing is that sizeof() of the array name and the pointer to the
> first array element differ.  But I used sizeof(array) here, so it should
> be correct.

Yup, the sizeof looks fine. I was really only puzzled about the &array part. But if it's standardized to return the same as array, then that's great and I can call myself more educated now :)


Alex

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