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

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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@xxxxxxx>
---

[...]

+
+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



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