On 1/25/2024 4:06 PM, Borislav Petkov wrote:
> On Wed, Dec 20, 2023 at 08:43:43PM +0530, Nikunj A Dadhania wrote:
>> @@ -307,11 +197,16 @@ static int verify_and_dec_payload(struct snp_guest_dev *snp_dev, void *payload,
>> * If the message size is greater than our buffer length then return
>> * an error.
>> */
>> - if (unlikely((resp_hdr->msg_sz + crypto->a_len) > sz))
>> + if (unlikely((resp_hdr->msg_sz + ctx->authsize) > sz))
>> return -EBADMSG;
>>
>> /* Decrypt the payload */
>> - return dec_payload(snp_dev, resp, payload, resp_hdr->msg_sz + crypto->a_len);
>> + memcpy(iv, &resp_hdr->msg_seqno, sizeof(resp_hdr->msg_seqno));
>
> sizeof(iv) != sizeof(resp_hdr->msg_seqno) and it fits now.
>
> However, for protection against future bugs, this should be:
>
> memcpy(iv, &resp_hdr->msg_seqno, min(sizeof(iv), sizeof(resp_hdr->msg_seqno)));
Sure, will change.
>
>> + if (!aesgcm_decrypt(ctx, payload, resp->payload, resp_hdr->msg_sz,
>> + &resp_hdr->algo, AAD_LEN, iv, resp_hdr->authtag))
>> + return -EBADMSG;
>> +
>> + return 0;
>> }
>>
>> static int enc_payload(struct snp_guest_dev *snp_dev, u64 seqno, int version, u8 type,
>> @@ -319,6 +214,8 @@ static int enc_payload(struct snp_guest_dev *snp_dev, u64 seqno, int version, u8
>> {
>> struct snp_guest_msg *req = &snp_dev->secret_request;
>> struct snp_guest_msg_hdr *hdr = &req->hdr;
>> + struct aesgcm_ctx *ctx = snp_dev->ctx;
>> + u8 iv[GCM_AES_IV_SIZE] = {};
>>
>> memset(req, 0, sizeof(*req));
>>
>> @@ -338,7 +235,14 @@ static int enc_payload(struct snp_guest_dev *snp_dev, u64 seqno, int version, u8
>> dev_dbg(snp_dev->dev, "request [seqno %lld type %d version %d sz %d]\n",
>> hdr->msg_seqno, hdr->msg_type, hdr->msg_version, hdr->msg_sz);
>>
>> - return __enc_payload(snp_dev, req, payload, sz);
>> + if (WARN_ON((sz + ctx->authsize) > sizeof(req->payload)))
>> + return -EBADMSG;
>> +
>> + memcpy(iv, &hdr->msg_seqno, sizeof(hdr->msg_seqno));
>
> Ditto.
Sure.
>
>> + aesgcm_encrypt(ctx, req->payload, payload, sz, &hdr->algo, AAD_LEN,
>> + iv, hdr->authtag);
>> +
>> + return 0;
>
Thanks,
Nikunj
