On Thu, Nov 18, 2021 at 10:32 AM Brijesh Singh [off-list ref] wrote:

On 11/17/21 5:34 PM, Peter Gonda wrote:

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+The guest ioctl should be issued on a file descriptor of the /dev/sev-guest device.
+The ioctl accepts struct snp_user_guest_request. The input and output structure is
+specified through the req_data and resp_data field respectively. If the ioctl fails
+to execute due to a firmware error, then fw_err code will be set.

Should way say what it will be set to? Also Sean pointed out on CCP
driver that 0 is strange to set the error to, its a uint so we cannot
do -1 like we did there. What about all FFs?

Sure, all FF's works, I can document and use it.

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+static inline u64 __snp_get_msg_seqno(struct snp_guest_dev *snp_dev)
+{
+       u64 count;

I may be overly paranoid here but how about
`lockdep_assert_held(&snp_cmd_mutex);` when writing or reading
directly from this data?

Sure, I can do it.

...

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+
+       if (rc)
+               return rc;
+
+       rc = verify_and_dec_payload(snp_dev, resp_buf, resp_sz);
+       if (rc) {
+               /*
+                * The verify_and_dec_payload() will fail only if the hypervisor is
+                * actively modifiying the message header or corrupting the encrypted payload.

modifiying

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+                * This hints that hypervisor is acting in a bad faith. Disable the VMPCK so that
+                * the key cannot be used for any communication.
+                */

This looks great, thanks for changes Brijesh. Should we mention in
comment here or at snp_disable_vmpck() the AES-GCM issues with
continuing to use the key? Or will future updaters to this code
understand already?

Sure, I can add comment about the AES-GCM.

...

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+
+/* See SNP spec SNP_GUEST_REQUEST section for the structure */
+enum msg_type {
+       SNP_MSG_TYPE_INVALID = 0,
+       SNP_MSG_CPUID_REQ,
+       SNP_MSG_CPUID_RSP,
+       SNP_MSG_KEY_REQ,
+       SNP_MSG_KEY_RSP,
+       SNP_MSG_REPORT_REQ,
+       SNP_MSG_REPORT_RSP,
+       SNP_MSG_EXPORT_REQ,
+       SNP_MSG_EXPORT_RSP,
+       SNP_MSG_IMPORT_REQ,
+       SNP_MSG_IMPORT_RSP,
+       SNP_MSG_ABSORB_REQ,
+       SNP_MSG_ABSORB_RSP,
+       SNP_MSG_VMRK_REQ,
+       SNP_MSG_VMRK_RSP,

Did you want to include MSG_ABSORB_NOMA_REQ and MSG_ABSORB_NOMA_RESP here?

Yes, I can includes those for the completeness.

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+struct snp_report_req {
+       /* message version number (must be non-zero) */
+       __u8 msg_version;
+
+       /* user data that should be included in the report */
+       __u8 user_data[64];

Are we missing the 'vmpl' field here? Does those default all requests
to be signed with VMPL0? Users might want to change that, they could
be using a paravisor.

Good question, so far I was thinking that guest kernel will provide its
vmpl level instead of accepted the vmpl level from the userspace. Do you
see a need for a userspace to provide this information ?

That seems fine. I am just confused because we are just encrypting
this struct as the payload for the PSP. Doesn't the message require a
struct that looks like 'snp_report_req_user_data' below?

snp_report_req{
       /* message version number (must be non-zero) */
       __u8 msg_version;

      /* user data that should be included in the report */
       struct snp_report_req_user_data;
};

struct snp_report_req_user_data {
  u8 user_data[64];
  u32 vmpl;
  u32 reserved;
};

thanks