linux-kernel - Re: [PATCH v2 2/6] KVM: MMU: don't drop spte if overwrite it from W to RO

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:	Wed, 17 Nov 2010 17:57:40 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 2/6] KVM: MMU: don't drop spte if overwrite it from
 W to RO

On 11/17/2010 05:42 PM, Marcelo Tosatti wrote:
> On Wed, Nov 17, 2010 at 12:10:50PM +0800, Xiao Guangrong wrote:
>> We just need flush tlb if overwrite a writable spte with a read-only
>> one.
>>
>> And we should move this operation to set_spte() for sync_page path
>>
>> Signed-off-by: Xiao Guangrong<xiaoguangrong@...fujitsu.com>
>> ---
>>   arch/x86/kvm/mmu.c |   20 +++++++++-----------
>>   1 files changed, 9 insertions(+), 11 deletions(-)
>>
>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>> index e008ae7..9bad960 100644
>> --- a/arch/x86/kvm/mmu.c
>> +++ b/arch/x86/kvm/mmu.c
>> @@ -1966,7 +1966,7 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
>>   		    gfn_t gfn, pfn_t pfn, bool speculative,
>>   		    bool can_unsync, bool reset_host_protection)
>>   {
>> -	u64 spte;
>> +	u64 spte, entry = *sptep;
>>   	int ret = 0;
>>
>>   	/*
>> @@ -2039,6 +2039,14 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
>>
>>   set_pte:
>>   	update_spte(sptep, spte);
>> +	/*
>> +	 * If we overwrite a writable spte with a read-only one we
>> +	 * should flush remote TLBs. Otherwise rmap_write_protect
>> +	 * will find a read-only spte, even though the writable spte
>> +	 * might be cached on a CPU's TLB.
>> +	 */
>> +	if (is_writable_pte(entry)&&  !is_writable_pte(*sptep))
>> +		kvm_flush_remote_tlbs(vcpu->kvm);
> There is no need to flush on sync_page path since the guest is
> responsible for it.
>

  If we don't, the next rmap_write_protect() will incorrectly decide 
that there's no need to flush tlbs.

--
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/