Re: [PATCH v11 42/45] virt: Add SEV-SNP guest driver

[Brijesh Singh <brijesh.singh@amd.com>]

Hi Dov,

On 3/2/22 04:03, Dov Murik wrote:
> Hi Brijesh,
> 
> On 24/02/2022 18:56, Brijesh Singh wrote:
>> The SEV-SNP specification provides the guest a mechanism to communicate
>> with the PSP without risk from a malicious hypervisor who wishes to
>> read, alter, drop or replay the messages sent. The driver uses
>> snp_issue_guest_request() to issue GHCB SNP_GUEST_REQUEST or
>> SNP_EXT_GUEST_REQUEST NAE events to submit the request to PSP.
>>
>> The PSP requires that all communication should be encrypted using key
>> specified through the platform_data.
>>
>> Userspace can use SNP_GET_REPORT ioctl() to query the guest attestation
>> report.
>>
>> See SEV-SNP spec section Guest Messages for more details.
>>
>> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
>> ---
> 
> [...]
> 
>> +
>> +static struct snp_guest_crypto *init_crypto(struct snp_guest_dev *snp_dev, u8 *key, size_t keylen)
>> +{
>> +	struct snp_guest_crypto *crypto;
>> +
>> +	crypto = kzalloc(sizeof(*crypto), GFP_KERNEL_ACCOUNT);
>> +	if (!crypto)
>> +		return NULL;
>> +
>> +	crypto->tfm = crypto_alloc_aead("gcm(aes)", 0, 0);
>> +	if (IS_ERR(crypto->tfm))
>> +		goto e_free;
> 
> 
> When trying this series, the sevguest module didn't load (and printed no
> error message).  After adding some debug messages, I found that the
> crypto_alloc_read() call returned an error.  I found out that
> CONFIG_CRYPTO_GCM was disabled in my config.
> 
> Consider modifying sevguest/Kconfig to force it in:
> 
> 
> 
> diff --git a/drivers/virt/coco/sevguest/Kconfig b/drivers/virt/coco/sevguest/Kconfig
> index 2be45820e86c..74ca1fe09437 100644
> --- a/drivers/virt/coco/sevguest/Kconfig
> +++ b/drivers/virt/coco/sevguest/Kconfig
> @@ -1,7 +1,9 @@
>   config SEV_GUEST
>          tristate "AMD SEV Guest driver"
>          default m
> -       depends on AMD_MEM_ENCRYPT && CRYPTO_AEAD2
> +       depends on AMD_MEM_ENCRYPT
> +       select CRYPTO_AEAD2
> +       select CRYPTO_GCM
>          help
>            SEV-SNP firmware provides the guest a mechanism to communicate with
>            the PSP without risk from a malicious hypervisor who wishes to read,
> 
> 
> 
> Another thing to consider is to add messages to the various error paths
> in snp_guest_probe().  Not sure what is the common practice in other modules.
> 

I am not sure about sparkling the error message on the various paths, 
but I agree with adding the 'select'.

If I happen to do v12, I will include it in my series; otherwise, the 
maintainer can pull your above fixup on top of it.

thanks for looking into it.

~Brijesh