linux-kernel - Re: [PATCH 2/6] KVM MMU: fix kvm_mmu_zap

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]

Date:	Mon, 12 Apr 2010 12:08:15 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	KVM list <kvm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/6] KVM MMU: fix kvm_mmu_zap_page() and its calling path

On 04/12/2010 11:53 AM, Xiao Guangrong wrote:
>>
>>>            kvm->arch.n_free_mmu_pages = 0;
>>> @@ -1589,7 +1589,8 @@ static void mmu_unshadow(struct kvm *kvm, gfn_t
>>> gfn)
>>>            &&   !sp->role.invalid) {
>>>                pgprintk("%s: zap %lx %x\n",
>>>                     __func__, gfn, sp->role.word);
>>> -            kvm_mmu_zap_page(kvm, sp);
>>> +            if (kvm_mmu_zap_page(kvm, sp))
>>> +                nn = bucket->first;
>>>            }
>>>        }
>>>
>>>        
>> I don't understand why this is needed.
>>      
> There is the code segment in mmu_unshadow():
>
> |hlist_for_each_entry_safe(sp, node, nn, bucket, hash_link) {
> |		if (sp->gfn == gfn&&  !sp->role.direct
> |		&&  !sp->role.invalid) {
> |			pgprintk("%s: zap %lx %x\n",
> |				 __func__, gfn, sp->role.word);
> |			kvm_mmu_zap_page(kvm, sp);
> |		}
> |	}
>
> in the loop, if nn is zapped, hlist_for_each_entry_safe() access nn will
> cause crash. and it's checked in other functions, such as kvm_mmu_zap_all(),
> kvm_mmu_unprotect_page()...
>    

hlist_for_each_entry_safe() is supposed to be be safe against removal of 
the element that is pointed to by the iteration cursor.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

--
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/