linux-kernel - Re: [PATCH 1/7] KVM: Write protect the updated slot only when we start dirty logging

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20121225130840.74996653.yoshikawa_takuya_b1@lab.ntt.co.jp>
Date:	Tue, 25 Dec 2012 13:08:40 +0900
From:	Takuya Yoshikawa <yoshikawa_takuya_b1@....ntt.co.jp>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	mtosatti@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/7] KVM: Write protect the updated slot only when we
 start dirty logging

On Mon, 24 Dec 2012 15:27:17 +0200
Gleb Natapov <gleb@...hat.com> wrote:

> > @@ -6897,7 +6897,14 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
> >  	spin_lock(&kvm->mmu_lock);
> >  	if (nr_mmu_pages)
> >  		kvm_mmu_change_mmu_pages(kvm, nr_mmu_pages);
> > -	kvm_mmu_slot_remove_write_access(kvm, mem->slot);
> > +	/*
> > +	 * Write protect all pages for dirty logging.
> > +	 * Existing largepage mappings are destroyed here and new ones will
> > +	 * not be created until the end of the logging.
> > +	 */
> > +	if ((mem->flags & KVM_MEM_LOG_DIRTY_PAGES) &&
> > +	    !(old.flags & KVM_MEM_LOG_DIRTY_PAGES))
> > +		kvm_mmu_slot_remove_write_access(kvm, mem->slot);
> We should not check old slot flags here or at least check that
> old.npages is not zero. Userspace may delete a slot using old flags,
> then, if new memslot is created with dirty log enabled, it will not be
> protected.

The flag, KVM_MEM_LOG_DIRTY_PAGES, is explicitely cleared when we
delete a slot to free dirty_bitmap:

	if (!npages)
		mem->flags &= ~KVM_MEM_LOG_DIRTY_PAGES;

So when old.npages is not zero, the second condition must be true.

Other parts are doing "if (!slot->dirty_bitmap)" to see if the slot
is in dirty logging mode.  If you prefer, we can do the same here.

Thanks,
	Takuya
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/