Re: [PATCH 2/5] crypto: ccp: Reject SEV commands with mismatching command buffer

From: Tom Lendacky <thomas.lendacky@amd.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Brijesh Singh <brijesh.singh@amd.com>,
	John Allen <john.allen@amd.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-crypto@vger.kernel.org,
	linux-kernel@vger.kernel.org, Borislav Petkov <bp@suse.de>
Subject: Re: [PATCH 2/5] crypto: ccp: Reject SEV commands with mismatching command buffer
Date: Mon, 5 Apr 2021 11:37:13 -0500	[thread overview]
Message-ID: <d79ac2a4-10f7-2ff1-fb66-d246348493fa@amd.com> (raw)
In-Reply-To: <YGs7vioH8TVzyckx@google.com>

On 4/5/21 11:33 AM, Sean Christopherson wrote:
> On Mon, Apr 05, 2021, Tom Lendacky wrote:
>> On 4/2/21 6:36 PM, Sean Christopherson wrote:
>>> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
>>> index 6556d220713b..4c513318f16a 100644
>>> --- a/drivers/crypto/ccp/sev-dev.c
>>> +++ b/drivers/crypto/ccp/sev-dev.c
>>> @@ -141,6 +141,7 @@ static int __sev_do_cmd_locked(int cmd, void *data, int *psp_ret)
>>>  	struct sev_device *sev;
>>>  	unsigned int phys_lsb, phys_msb;
>>>  	unsigned int reg, ret = 0;
>>> +	int buf_len;
>>>  
>>>  	if (!psp || !psp->sev_data)
>>>  		return -ENODEV;
>>> @@ -150,7 +151,11 @@ static int __sev_do_cmd_locked(int cmd, void *data, int *psp_ret)
>>>  
>>>  	sev = psp->sev_data;
>>>  
>>> -	if (data && WARN_ON_ONCE(is_vmalloc_addr(data)))
>>> +	buf_len = sev_cmd_buffer_len(cmd);
>>> +	if (WARN_ON_ONCE(!!data != !!buf_len))
>>
>> Seems a bit confusing to me.  Can this just be:
>>
>> 	if (WARN_ON_ONCE(data && !buf_len))
> 
> Or as Christophe pointed out, "!data != !buf_len".
> 
>> Or is this also trying to catch the case where buf_len is non-zero but
>> data is NULL?
> 
> Ya.  It's not necessary to detect "buf_len && !data", but it doesn't incur
> additional cost.  Is there a reason _not_ to disallow that?

Nope, no reason. I was just trying to process all the not signs :)

Thanks,
Tom

> 