netdev - Re: [PATCH 05/13] HV: Add Write/Read MSR registers via ghcb page

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, 2 Aug 2021 21:18:15 +0800
From:   Tianyu Lan <ltykernel@...il.com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        wei.liu@...nel.org, decui@...rosoft.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com,
        dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
        konrad.wilk@...cle.com, boris.ostrovsky@...cle.com,
        jgross@...e.com, sstabellini@...nel.org, will@...nel.org,
        davem@...emloft.net, kuba@...nel.org, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, arnd@...db.de, hch@....de,
        m.szyprowski@...sung.com, robin.murphy@....com,
        thomas.lendacky@....com, brijesh.singh@....com, ardb@...nel.org,
        Tianyu.Lan@...rosoft.com, rientjes@...gle.com,
        martin.b.radev@...il.com, akpm@...ux-foundation.org,
        rppt@...nel.org, kirill.shutemov@...ux.intel.com,
        aneesh.kumar@...ux.ibm.com, krish.sadhukhan@...cle.com,
        saravanand@...com, xen-devel@...ts.xenproject.org,
        pgonda@...gle.com, david@...hat.com, keescook@...omium.org,
        hannes@...xchg.org, sfr@...b.auug.org.au,
        michael.h.kelley@...rosoft.com, iommu@...ts.linux-foundation.org,
        linux-arch@...r.kernel.org, linux-hyperv@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
        netdev@...r.kernel.org, vkuznets@...hat.com, anparri@...rosoft.com
Subject: Re: [PATCH 05/13] HV: Add Write/Read MSR registers via ghcb page

On 8/2/2021 8:28 PM, Joerg Roedel wrote:
> On Wed, Jul 28, 2021 at 10:52:20AM -0400, Tianyu Lan wrote:
>> +void hv_ghcb_msr_write(u64 msr, u64 value)
>> +{
>> +	union hv_ghcb *hv_ghcb;
>> +	void **ghcb_base;
>> +	unsigned long flags;
>> +
>> +	if (!ms_hyperv.ghcb_base)
>> +		return;
>> +
>> +	WARN_ON(in_nmi());
>> +
>> +	local_irq_save(flags);
>> +	ghcb_base = (void **)this_cpu_ptr(ms_hyperv.ghcb_base);
>> +	hv_ghcb = (union hv_ghcb *)*ghcb_base;
>> +	if (!hv_ghcb) {
>> +		local_irq_restore(flags);
>> +		return;
>> +	}
>> +
>> +	memset(hv_ghcb, 0x00, HV_HYP_PAGE_SIZE);
> 
> Do you really need to zero out the whole 4k? The validation bitmap
> should be enough, there are no secrets on the page anyway.
> Same in hv_ghcb_msr_read().

OK. Thanks for suggestion. I will have a try.

> 
>> +enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
>> +				   struct es_em_ctxt *ctxt,
>> +				   u64 exit_code, u64 exit_info_1,
>> +				   u64 exit_info_2)
>>   {
>>   	enum es_result ret;
>>   
>> @@ -109,7 +109,16 @@ static enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
>>   	ghcb_set_sw_exit_info_1(ghcb, exit_info_1);
>>   	ghcb_set_sw_exit_info_2(ghcb, exit_info_2);
>>   
>> -	sev_es_wr_ghcb_msr(__pa(ghcb));
>> +	/*
>> +	 * Hyper-V runs paravisor with SEV. Ghcb page is allocated by
>> +	 * paravisor and not needs to be updated in the Linux guest.
>> +	 * Otherwise, the ghcb page's PA reported by paravisor is above
>> +	 * VTOM. Hyper-V use this function with NULL for ctxt point and
>> +	 * skip setting ghcb page in such case.
>> +	 */
>> +	if (ctxt)
>> +		sev_es_wr_ghcb_msr(__pa(ghcb));
> 
> No, do not make this function work with ctxt==NULL. Instead, factor out
> a helper function which contains what Hyper-V needs and use that in
> sev_es_ghcb_hv_call() and Hyper-V code.
> 

OK. Will update.

>> +union hv_ghcb {
>> +	struct ghcb ghcb;
>> +} __packed __aligned(PAGE_SIZE);
> 
> I am curious what this will end up being good for.
> 

Hyper-V introduces a specific hypercall request in GHCB page and use 
same union in the Linux Hyper-V code to read/write MSR and call the new 
hypercall request.