Re: [PATCH v2 04/11] virt: sev-guest: Add simplified helper to assign vmpck

[Nikunj A. Dadhania]

On 4/4/2023 1:56 AM, Tom Lendacky wrote:
> On 3/26/23 09:46, Nikunj A Dadhania wrote:
>> Simplify get_vmpck and prepare it to be used as an API. Update the
>> snp_guest_dev structure in snp_assign_vmpck(). Added vmpck_id to the
>> snp_guest_dev structure which can be used in SNP guest request API and
>> will remove direct use of vmpck_id command line parameter.
> 
> This needs to say more about why you're doing this. The first two 
> sentences need more explanation as they don't really stand on their own.
> How about the this:

Add vmpck_id to snp_guest_dev struct instead of directly using vmpck_id 
command line parameter. Each SNP guest has four VMPCK, which the firmware 
generates and provides to the guest in a special secrets page. Each VMPCK 
has a sequence number. Simplify assignment of key and sequence number 
instead of using a switch case.

> The last sentence talks about removing direct use of vmpck_id, so you 
> should probably do that in this patch since it seems to be the real 
> reason for all this.

I did change all places using vmpck_id to snp_dev->vmpck_id. This is the 
only place the command line parameter is being used.

+       if (!snp_assign_vmpck(snp_dev, vmpck_id)) {

Regards
Nikunj

> 
> Thanks,
> Tom
> 
>>
>> Signed-off-by: Nikunj A Dadhania <nikunj@xxxxxxx>
>> ---
>>   drivers/virt/coco/sev-guest/sev-guest.c | 41 ++++++++-----------------
>>   1 file changed, 12 insertions(+), 29 deletions(-)
>>
>> diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
>> index ec93dee330f2..4901ebc8fa1a 100644
>> --- a/drivers/virt/coco/sev-guest/sev-guest.c
>> +++ b/drivers/virt/coco/sev-guest/sev-guest.c
>> @@ -45,6 +45,7 @@ struct snp_guest_dev {
>>       struct snp_req_data input;
>>       u32 *os_area_msg_seqno;
>>       u8 *vmpck;
>> +    u8 vmpck_id;
>>   };
>>     static u32 vmpck_id;
>> @@ -80,7 +81,7 @@ static inline unsigned int get_ctx_authsize(struct snp_guest_dev *snp_dev)
>>   static void snp_disable_vmpck(struct snp_guest_dev *snp_dev)
>>   {
>>       dev_alert(snp_dev->dev, "Disabling vmpck_id %d to prevent IV reuse.\n",
>> -          vmpck_id);
>> +          snp_dev->vmpck_id);
>>       memzero_explicit(snp_dev->vmpck, VMPCK_KEY_LEN);
>>       snp_dev->vmpck = NULL;
>>   }
>> @@ -339,7 +340,7 @@ static int snp_send_guest_request(struct snp_guest_dev *snp_dev, struct snp_gues
>>       memset(snp_dev->response, 0, sizeof(struct snp_guest_msg));
>>         /* Encrypt the userspace provided payload */
>> -    rc = enc_payload(snp_dev, seqno, req, vmpck_id);
>> +    rc = enc_payload(snp_dev, seqno, req, snp_dev->vmpck_id);
>>       if (rc)
>>           return rc;
>>   @@ -364,7 +365,6 @@ static int snp_send_guest_request(struct snp_guest_dev *snp_dev, struct snp_gues
>>       return 0;
>>   }
>>   -
>>   static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, u8 msg_version,
>>                   u8 msg_type, void *req_buf, size_t req_sz, void *resp_buf,
>>                   u32 resp_sz, __u64 *fw_err)
>> @@ -625,32 +625,16 @@ static const struct file_operations snp_guest_fops = {
>>       .unlocked_ioctl = snp_guest_ioctl,
>>   };
>>   -static u8 *get_vmpck(int id, struct snp_secrets_page_layout *layout, u32 **seqno)
>> +bool snp_assign_vmpck(struct snp_guest_dev *dev, int vmpck_id)
>>   {
>> -    u8 *key = NULL;
>> +    if (WARN_ON(vmpck_id > 3))
>> +        return false;
>>   -    switch (id) {
>> -    case 0:
>> -        *seqno = &layout->os_area.msg_seqno_0;
>> -        key = layout->vmpck0;
>> -        break;
>> -    case 1:
>> -        *seqno = &layout->os_area.msg_seqno_1;
>> -        key = layout->vmpck1;
>> -        break;
>> -    case 2:
>> -        *seqno = &layout->os_area.msg_seqno_2;
>> -        key = layout->vmpck2;
>> -        break;
>> -    case 3:
>> -        *seqno = &layout->os_area.msg_seqno_3;
>> -        key = layout->vmpck3;
>> -        break;
>> -    default:
>> -        break;
>> -    }
>> +    dev->vmpck_id = vmpck_id;
>> +    dev->vmpck = dev->layout->vmpck0 + vmpck_id * VMPCK_KEY_LEN;
>> +    dev->os_area_msg_seqno = &dev->layout->os_area.msg_seqno_0 + vmpck_id;
>>   -    return key;
>> +    return true;
>>   }
>>     static int __init sev_guest_probe(struct platform_device *pdev)
>> @@ -682,8 +666,8 @@ static int __init sev_guest_probe(struct platform_device *pdev)
>>           goto e_unmap;
>>         ret = -EINVAL;
>> -    snp_dev->vmpck = get_vmpck(vmpck_id, layout, &snp_dev->os_area_msg_seqno);
>> -    if (!snp_dev->vmpck) {
>> +    snp_dev->layout = layout;
>> +    if (!snp_assign_vmpck(snp_dev, vmpck_id)) {
>>           dev_err(dev, "invalid vmpck id %d\n", vmpck_id);
>>           goto e_unmap;
>>       }
>> @@ -697,7 +681,6 @@ static int __init sev_guest_probe(struct platform_device *pdev)
>>       mutex_init(&snp_dev->cmd_mutex);
>>       platform_set_drvdata(pdev, snp_dev);
>>       snp_dev->dev = dev;
>> -    snp_dev->layout = layout;
>>         /* Allocate the shared page used for the request and response message. */
>>       snp_dev->request = alloc_shared_pages(dev, sizeof(struct snp_guest_msg));