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Date:   Wed, 2 Mar 2022 08:33:20 -0600
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Cc:     brijesh.singh@amd.com, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ard Biesheuvel <ardb@kernel.org>,
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        Sean Christopherson <seanjc@google.com>,
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        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
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        Peter Zijlstra <peterz@infradead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Tobin Feldman-Fitzthum <tobin@ibm.com>,
        Borislav Petkov <bp@alien8.de>,
        Michael Roth <michael.roth@amd.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Andi Kleen <ak@linux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        brijesh.ksingh@gmail.com, tony.luck@intel.com, marcorr@google.com,
        sathyanarayanan.kuppuswamy@linux.intel.com
Subject: Re: [PATCH v11 42/45] virt: Add SEV-SNP guest driver
Content-Language: en-US
To:     Dov Murik <dovmurik@linux.ibm.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        linux-efi@vger.kernel.org, platform-driver-x86@vger.kernel.org,
        linux-coco@lists.linux.dev, linux-mm@kvack.org
References: <20220224165625.2175020-1-brijesh.singh@amd.com>
 <20220224165625.2175020-43-brijesh.singh@amd.com>
 <c197dc02-b63a-eb45-8e52-275934177d7e@linux.ibm.com>
From:   Brijesh Singh <brijesh.singh@amd.com>
In-Reply-To: <c197dc02-b63a-eb45-8e52-275934177d7e@linux.ibm.com>
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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