From patchwork Fri Oct 21 17:33:28 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Peter Gonda X-Patchwork-Id: 13015195 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A40EAC433FE for ; Fri, 21 Oct 2022 17:33:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230143AbiJURdj (ORCPT ); Fri, 21 Oct 2022 13:33:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35274 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229853AbiJURdh (ORCPT ); Fri, 21 Oct 2022 13:33:37 -0400 Received: from mail-pl1-x649.google.com (mail-pl1-x649.google.com [IPv6:2607:f8b0:4864:20::649]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 91DB626205B for ; Fri, 21 Oct 2022 10:33:36 -0700 (PDT) Received: by mail-pl1-x649.google.com with SMTP id w11-20020a170902e88b00b001855276704aso2050412plg.4 for ; Fri, 21 Oct 2022 10:33:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:from:subject:mime-version:message-id:date:from:to:cc:subject :date:message-id:reply-to; bh=Rm31qAFaq+M5EgnK0auSpdF+G0fRaJUMCym7D7tYLvw=; b=YrHCpg3QEb9QJEUkOK3NXTmjU0qVBg1fZfBzLdxZoVUVe0ZbDSdSlLJs50rvbe0zL6 2i2fHKgaCdM4MDMWA5FB4J4yF4zEfp+172NtQvekyq98xeDI6wNceG2aYhaUu/hujtnI YofEh9QFhpuWWjI9yEK5Ctgai33+KfV9F5nHvKjHs6OOgZRrC9TeP4Id6FfXZOYFx1ks zVArlk9s0+tGOBcHEMb61aVIfLhlw1x8KzO95Zn1gAq/c+BgeUb/hVGf43b04o7hLrr5 3ktFYcBGfUHLyUkDqJXHQIZ/ynGYfinJFlUSXEIMvDpv47Hq+Ur+ogXGIiUf+MdJxl7L ijXA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:from:subject:mime-version:message-id:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=Rm31qAFaq+M5EgnK0auSpdF+G0fRaJUMCym7D7tYLvw=; b=VfULks8QSBy0racrQbJEzstLzdxUelZ1djSJdjNm5rsX8dMsAU9FfBUPNLC72nfo74 vOR9qkdD0PbX3pBP8J56fK/pjN4cNOZdeajr18U47tsHmG0dyS3BB9TKAWwB+dtKXjX/ s9q5Y3W515z/vq9FkatvFf1cvUlsxiub9cM1KEEhfy/x7diLJBF37N8VmiSH805isMPr tDHcIDQCCGgp17NUV97wmu58AjCoIr32YlKvsmXgdabVt7imIeZmLy2khQWeHr7j5bhw TUkb5JvHAohf8Irnc0BM7eUBcxRLyKav7kF7wV0BOLbxWUpHkJl3apBl6XXhv+ztzRaz 4x7g== X-Gm-Message-State: ACrzQf2yH/+Z2UIq9sumH/Tam4mGXqvIqLQGB5Z+yl8KMAb2xL/E8R6u 6tU1zIznrair79zEC9e5L/dkcJOUZrM= X-Google-Smtp-Source: AMsMyM4fVZqqp2S5uhWZHjdVvRNZU+skQdKq/j16fQ/MICKD5HU6uWA/WkxAVI1JxfGo+yZxrVtCIqMNGng= X-Received: from pgonda1.kir.corp.google.com ([2620:15c:29:203:3e70:6547:73ac:76aa]) (user=pgonda job=sendgmr) by 2002:a17:902:cecf:b0:185:475a:4073 with SMTP id d15-20020a170902cecf00b00185475a4073mr20663741plg.60.1666373616083; Fri, 21 Oct 2022 10:33:36 -0700 (PDT) Date: Fri, 21 Oct 2022 10:33:28 -0700 Message-Id: <20221021173328.2489411-1-pgonda@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.38.0.135.g90850a2211-goog Subject: [PATCH V2] virt: Prevent IV reuse in SNP guest driver From: Peter Gonda To: thomas.lendacky@amd.com Cc: Peter Gonda , Dionna Glaze , Borislav Petkov , Michael Roth , Haowen Bai , Yang Yingliang , Marc Orr , David Rientjes , Ashish Kalra , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org The ASP and an SNP guest use a series of AES-GCM keys called VMPCKs to communicate securely with each other. The IV to this scheme is a sequence number that both the ASP and the guest track. Currently this sequence number in a guest request must exactly match the sequence number tracked by the ASP. This means that if the guest sees an error from the host during a request it can only retry that exact request or disable the VMPCK to prevent an IV reuse. AES-GCM cannot tolerate IV reuse see: https://csrc.nist.gov/csrc/media/projects/block-cipher-techniques/documents/bcm/comments/800-38-series-drafts/gcm/joux_comments.pdf To handle userspace querying the cert_data length. Instead of requesting the cert length from userspace use the size of the drivers allocated shared buffer. Then copy that buffer to userspace, or give userspace an error depending on the size of the buffer given by userspace. Fixes: fce96cf044308 ("virt: Add SEV-SNP guest driver") Signed-off-by: Peter Gonda Reported-by: Peter Gonda Reviewed-by: Dionna Glaze Cc: Borislav Petkov Cc: Tom Lendacky Cc: Michael Roth Cc: Haowen Bai Cc: Yang Yingliang Cc: Marc Orr Cc: David Rientjes Cc: Ashish Kalra Cc: linux-kernel@vger.kernel.org Cc: kvm@vger.kernel.org --- drivers/virt/coco/sev-guest/sev-guest.c | 93 ++++++++++++++++--------- 1 file changed, 62 insertions(+), 31 deletions(-) diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c index f422f9c58ba7..8c54ea84bc57 100644 --- a/drivers/virt/coco/sev-guest/sev-guest.c +++ b/drivers/virt/coco/sev-guest/sev-guest.c @@ -41,7 +41,7 @@ struct snp_guest_dev { struct device *dev; struct miscdevice misc; - void *certs_data; + u8 (*certs_data)[SEV_FW_BLOB_MAX_SIZE]; struct snp_guest_crypto *crypto; struct snp_guest_msg *request, *response; struct snp_secrets_page_layout *layout; @@ -67,8 +67,27 @@ static bool is_vmpck_empty(struct snp_guest_dev *snp_dev) return true; } +/* + * If we receive an error from the host or ASP we have two options. We can + * either retry the exact same encrypted request or we can discontinue using the + * VMPCK. + * + * This is because in the current encryption scheme GHCB v2 uses AES-GCM to + * encrypt the requests. The IV for this scheme is the sequence number. GCM + * cannot tolerate IV reuse. + * + * The ASP FW v1.51 only increments the sequence numbers on a successful + * guest<->ASP back and forth and only accepts messages at its exact sequence + * number. + * + * So if we were to reuse the sequence number the encryption scheme is + * vulnerable. If we encrypt the sequence number for a fresh IV the ASP will + * reject our request. + */ static void snp_disable_vmpck(struct snp_guest_dev *snp_dev) { + dev_alert(snp_dev->dev, "Disabling vmpck_id: %d to prevent IV reuse.\n", + vmpck_id); memzero_explicit(snp_dev->vmpck, VMPCK_KEY_LEN); snp_dev->vmpck = NULL; } @@ -326,29 +345,29 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in if (fw_err) *fw_err = err; - if (rc) - return rc; + if (rc) { + dev_alert(snp_dev->dev, + "Detected error from ASP request. rc: %d, fw_err: %llu\n", + rc, *fw_err); + goto disable_vmpck; + } - /* - * The verify_and_dec_payload() will fail only if the hypervisor is - * actively modifying the message header or corrupting the encrypted payload. - * This hints that hypervisor is acting in a bad faith. Disable the VMPCK so that - * the key cannot be used for any communication. The key is disabled to ensure - * that AES-GCM does not use the same IV while encrypting the request payload. - */ rc = verify_and_dec_payload(snp_dev, resp_buf, resp_sz); if (rc) { dev_alert(snp_dev->dev, - "Detected unexpected decode failure, disabling the vmpck_id %d\n", - vmpck_id); - snp_disable_vmpck(snp_dev); - return rc; + "Detected unexpected decode failure from ASP. rc: %d\n", + rc); + goto disable_vmpck; } /* Increment to new message sequence after payload decryption was successful. */ snp_inc_msg_seqno(snp_dev); return 0; + +disable_vmpck: + snp_disable_vmpck(snp_dev); + return rc; } static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg) @@ -437,7 +456,7 @@ static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_reques struct snp_guest_crypto *crypto = snp_dev->crypto; struct snp_ext_report_req req; struct snp_report_resp *resp; - int ret, npages = 0, resp_len; + int ret, resp_len, req_cert_len, resp_cert_len; lockdep_assert_held(&snp_cmd_mutex); @@ -448,14 +467,15 @@ static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_reques return -EFAULT; /* userspace does not want certificate data */ - if (!req.certs_len || !req.certs_address) + req_cert_len = req.certs_len; + if (!req_cert_len || !req.certs_address) goto cmd; - if (req.certs_len > SEV_FW_BLOB_MAX_SIZE || - !IS_ALIGNED(req.certs_len, PAGE_SIZE)) + if (req_cert_len > sizeof(*snp_dev->certs_data) || + !IS_ALIGNED(req_cert_len, PAGE_SIZE)) return -EINVAL; - if (!access_ok((const void __user *)req.certs_address, req.certs_len)) + if (!access_ok((const void __user *)req.certs_address, req_cert_len)) return -EFAULT; /* @@ -464,8 +484,7 @@ static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_reques * the host. If host does not supply any certs in it, then copy * zeros to indicate that certificate data was not provided. */ - memset(snp_dev->certs_data, 0, req.certs_len); - npages = req.certs_len >> PAGE_SHIFT; + memset(snp_dev->certs_data, 0, sizeof(*snp_dev->certs_data)); cmd: /* * The intermediate response buffer is used while decrypting the @@ -477,25 +496,37 @@ static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_reques if (!resp) return -ENOMEM; - snp_dev->input.data_npages = npages; + snp_dev->input.data_npages = sizeof(*snp_dev->certs_data) >> PAGE_SHIFT; ret = handle_guest_request(snp_dev, SVM_VMGEXIT_EXT_GUEST_REQUEST, arg->msg_version, SNP_MSG_REPORT_REQ, &req.data, sizeof(req.data), resp->data, resp_len, &arg->fw_err); + resp_cert_len = snp_dev->input.data_npages << PAGE_SHIFT; + /* If certs length is invalid then copy the returned length */ if (arg->fw_err == SNP_GUEST_REQ_INVALID_LEN) { - req.certs_len = snp_dev->input.data_npages << PAGE_SHIFT; + dev_alert(snp_dev->dev, + "Certificate data from host: %d, Max size allocated by driver: %lu.\n", + resp_cert_len, sizeof(*snp_dev->certs_data)); + ret = -EFAULT; + } + + if (ret) + goto e_free; + + /* Pass the actual certificate data size back to userspace */ + req.certs_len = resp_cert_len; + if (resp_cert_len > req_cert_len) { + arg->fw_err = SNP_GUEST_REQ_INVALID_LEN; if (copy_to_user((void __user *)arg->req_data, &req, sizeof(req))) ret = -EFAULT; - } - if (ret) goto e_free; + } - if (npages && - copy_to_user((void __user *)req.certs_address, snp_dev->certs_data, - req.certs_len)) { + if (copy_to_user((void __user *)req.certs_address, snp_dev->certs_data, + resp_cert_len)) { ret = -EFAULT; goto e_free; } @@ -676,7 +707,7 @@ static int __init sev_guest_probe(struct platform_device *pdev) if (!snp_dev->response) goto e_free_request; - snp_dev->certs_data = alloc_shared_pages(dev, SEV_FW_BLOB_MAX_SIZE); + snp_dev->certs_data = alloc_shared_pages(dev, sizeof(*snp_dev->certs_data)); if (!snp_dev->certs_data) goto e_free_response; @@ -703,7 +734,7 @@ static int __init sev_guest_probe(struct platform_device *pdev) return 0; e_free_cert_data: - free_shared_pages(snp_dev->certs_data, SEV_FW_BLOB_MAX_SIZE); + free_shared_pages(snp_dev->certs_data, sizeof(*snp_dev->certs_data)); e_free_response: free_shared_pages(snp_dev->response, sizeof(struct snp_guest_msg)); e_free_request: @@ -717,7 +748,7 @@ static int __exit sev_guest_remove(struct platform_device *pdev) { struct snp_guest_dev *snp_dev = platform_get_drvdata(pdev); - free_shared_pages(snp_dev->certs_data, SEV_FW_BLOB_MAX_SIZE); + free_shared_pages(snp_dev->certs_data, sizeof(*snp_dev->certs_data)); free_shared_pages(snp_dev->response, sizeof(struct snp_guest_msg)); free_shared_pages(snp_dev->request, sizeof(struct snp_guest_msg)); deinit_crypto(snp_dev->crypto);