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

Tom Lendacky
2021-04-05T16:37:22Z

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

>