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

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Date:   Wed, 2 Mar 2022 08:33:20 -0600
From:   Brijesh Singh <brijesh.singh@....com>
To:     Dov Murik <dovmurik@...ux.ibm.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org
Cc:     brijesh.singh@....com, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Borislav Petkov <bp@...en8.de>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        brijesh.ksingh@...il.com, tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH v11 42/45] virt: Add SEV-SNP guest driver

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@....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