Re: [PATCH v5 01/14] virt: sev-guest: Use AES GCM crypto library

[Tom Lendacky <thomas.lendacky@amd.com>]

On 10/30/23 01:36, Nikunj A Dadhania wrote:
> The sev-guest driver encryption code uses Crypto API for SNP guest
> messaging to interact with AMD Security processor. For enabling SecureTSC,
> SEV-SNP guests need to send a TSC_INFO request guest message before the
> smpboot phase starts. Details from the TSC_INFO response will be used to
> program the VMSA before the secondary CPUs are brought up. The Crypto API
> is not available this early in the boot phase.
> 
> In preparation of moving the encryption code out of sev-guest driver to
> support SecureTSC and make reviewing the diff easier, start using AES GCM
> library implementation instead of Crypto API.
> 
> CC: Ard Biesheuvel <ardb@kernel.org>
> Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
> Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>

I just a few nit comments that might be nice to cover if you have to do a 
v6...

> ---
>   drivers/virt/coco/sev-guest/Kconfig     |   4 +-
>   drivers/virt/coco/sev-guest/sev-guest.c | 163 ++++++------------------
>   drivers/virt/coco/sev-guest/sev-guest.h |   3 +
>   3 files changed, 44 insertions(+), 126 deletions(-)
> 
> diff --git a/drivers/virt/coco/sev-guest/Kconfig b/drivers/virt/coco/sev-guest/Kconfig
> index da2d7ca531f0..bcc760bfb468 100644
> --- a/drivers/virt/coco/sev-guest/Kconfig
> +++ b/drivers/virt/coco/sev-guest/Kconfig
> @@ -2,9 +2,7 @@ config SEV_GUEST
>   	tristate "AMD SEV Guest driver"
>   	default m
>   	depends on AMD_MEM_ENCRYPT
> -	select CRYPTO
> -	select CRYPTO_AEAD2
> -	select CRYPTO_GCM
> +	select CRYPTO_LIB_AESGCM
>   	help
>   	  SEV-SNP firmware provides the guest a mechanism to communicate with
>   	  the PSP without risk from a malicious hypervisor who wishes to read,
> diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
> index 97dbe715e96a..68044c436866 100644
> --- a/drivers/virt/coco/sev-guest/sev-guest.c
> +++ b/drivers/virt/coco/sev-guest/sev-guest.c
> @@ -16,8 +16,7 @@
>   #include <linux/miscdevice.h>
>   #include <linux/set_memory.h>
>   #include <linux/fs.h>
> -#include <crypto/aead.h>
> -#include <linux/scatterlist.h>
> +#include <crypto/gcm.h>
>   #include <linux/psp-sev.h>
>   #include <uapi/linux/sev-guest.h>
>   #include <uapi/linux/psp-sev.h>
> @@ -28,24 +27,16 @@
>   #include "sev-guest.h"
>   
>   #define DEVICE_NAME	"sev-guest"
> -#define AAD_LEN		48
> -#define MSG_HDR_VER	1
>   
>   #define SNP_REQ_MAX_RETRY_DURATION	(60*HZ)
>   #define SNP_REQ_RETRY_DELAY		(2*HZ)
>   
> -struct snp_guest_crypto {
> -	struct crypto_aead *tfm;
> -	u8 *iv, *authtag;
> -	int iv_len, a_len;
> -};
> -
>   struct snp_guest_dev {
>   	struct device *dev;
>   	struct miscdevice misc;
>   
>   	void *certs_data;
> -	struct snp_guest_crypto *crypto;
> +	struct aesgcm_ctx *ctx;
>   	/* request and response are in unencrypted memory */
>   	struct snp_guest_msg *request, *response;
>   
> @@ -152,132 +143,59 @@ static inline struct snp_guest_dev *to_snp_dev(struct file *file)
>   	return container_of(dev, struct snp_guest_dev, misc);
>   }
>   
> -static struct snp_guest_crypto *init_crypto(struct snp_guest_dev *snp_dev, u8 *key, size_t keylen)
> +static struct aesgcm_ctx *snp_init_crypto(u8 *key, size_t keylen)
>   {
> -	struct snp_guest_crypto *crypto;
> +	struct aesgcm_ctx *ctx;
>   
> -	crypto = kzalloc(sizeof(*crypto), GFP_KERNEL_ACCOUNT);
> -	if (!crypto)
> +	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL_ACCOUNT);
> +	if (!ctx)
>   		return NULL;
>   
> -	crypto->tfm = crypto_alloc_aead("gcm(aes)", 0, 0);
> -	if (IS_ERR(crypto->tfm))
> -		goto e_free;
> -
> -	if (crypto_aead_setkey(crypto->tfm, key, keylen))
> -		goto e_free_crypto;
> -
> -	crypto->iv_len = crypto_aead_ivsize(crypto->tfm);
> -	crypto->iv = kmalloc(crypto->iv_len, GFP_KERNEL_ACCOUNT);
> -	if (!crypto->iv)
> -		goto e_free_crypto;
> -
> -	if (crypto_aead_authsize(crypto->tfm) > MAX_AUTHTAG_LEN) {
> -		if (crypto_aead_setauthsize(crypto->tfm, MAX_AUTHTAG_LEN)) {
> -			dev_err(snp_dev->dev, "failed to set authsize to %d\n", MAX_AUTHTAG_LEN);
> -			goto e_free_iv;
> -		}
> +	if (aesgcm_expandkey(ctx, key, keylen, AUTHTAG_LEN)) {
> +		pr_err("SNP: crypto init failed\n");
> +		kfree(ctx);
> +		return NULL;
>   	}
>   
> -	crypto->a_len = crypto_aead_authsize(crypto->tfm);
> -	crypto->authtag = kmalloc(crypto->a_len, GFP_KERNEL_ACCOUNT);
> -	if (!crypto->authtag)
> -		goto e_free_iv;
> -
> -	return crypto;
> -
> -e_free_iv:
> -	kfree(crypto->iv);
> -e_free_crypto:
> -	crypto_free_aead(crypto->tfm);
> -e_free:
> -	kfree(crypto);
> -
> -	return NULL;
> -}
> -
> -static void deinit_crypto(struct snp_guest_crypto *crypto)
> -{
> -	crypto_free_aead(crypto->tfm);
> -	kfree(crypto->iv);
> -	kfree(crypto->authtag);
> -	kfree(crypto);
> -}
> -
> -static int enc_dec_message(struct snp_guest_crypto *crypto, struct snp_guest_msg *msg,
> -			   u8 *src_buf, u8 *dst_buf, size_t len, bool enc)
> -{
> -	struct snp_guest_msg_hdr *hdr = &msg->hdr;
> -	struct scatterlist src[3], dst[3];
> -	DECLARE_CRYPTO_WAIT(wait);
> -	struct aead_request *req;
> -	int ret;
> -
> -	req = aead_request_alloc(crypto->tfm, GFP_KERNEL);
> -	if (!req)
> -		return -ENOMEM;
> -
> -	/*
> -	 * AEAD memory operations:
> -	 * +------ AAD -------+------- DATA -----+---- AUTHTAG----+
> -	 * |  msg header      |  plaintext       |  hdr->authtag  |
> -	 * | bytes 30h - 5Fh  |    or            |                |
> -	 * |                  |   cipher         |                |
> -	 * +------------------+------------------+----------------+
> -	 */
> -	sg_init_table(src, 3);
> -	sg_set_buf(&src[0], &hdr->algo, AAD_LEN);
> -	sg_set_buf(&src[1], src_buf, hdr->msg_sz);
> -	sg_set_buf(&src[2], hdr->authtag, crypto->a_len);
> -
> -	sg_init_table(dst, 3);
> -	sg_set_buf(&dst[0], &hdr->algo, AAD_LEN);
> -	sg_set_buf(&dst[1], dst_buf, hdr->msg_sz);
> -	sg_set_buf(&dst[2], hdr->authtag, crypto->a_len);
> -
> -	aead_request_set_ad(req, AAD_LEN);
> -	aead_request_set_tfm(req, crypto->tfm);
> -	aead_request_set_callback(req, 0, crypto_req_done, &wait);
> -
> -	aead_request_set_crypt(req, src, dst, len, crypto->iv);
> -	ret = crypto_wait_req(enc ? crypto_aead_encrypt(req) : crypto_aead_decrypt(req), &wait);
> -
> -	aead_request_free(req);
> -	return ret;
> +	return ctx;
>   }
>   
> -static int __enc_payload(struct snp_guest_dev *snp_dev, struct snp_guest_msg *msg,
> +static int __enc_payload(struct aesgcm_ctx *ctx, struct snp_guest_msg *msg,
>   			 void *plaintext, size_t len)
>   {
> -	struct snp_guest_crypto *crypto = snp_dev->crypto;
>   	struct snp_guest_msg_hdr *hdr = &msg->hdr;
> +	u8 iv[GCM_AES_IV_SIZE] = {};
>   
> -	memset(crypto->iv, 0, crypto->iv_len);
> -	memcpy(crypto->iv, &hdr->msg_seqno, sizeof(hdr->msg_seqno));
> +	if (WARN_ON((hdr->msg_sz + ctx->authsize) > sizeof(msg->payload)))
> +		return -EBADMSG;
>   
> -	return enc_dec_message(crypto, msg, plaintext, msg->payload, len, true);
> +	memcpy(iv, &hdr->msg_seqno, sizeof(hdr->msg_seqno));
> +	aesgcm_encrypt(ctx, msg->payload, plaintext, len, &hdr->algo, AAD_LEN,
> +		       iv, hdr->authtag);
> +	return 0;
>   }

__enc_payload() is pretty small now and can probably just be part of the 
only function that calls it, enc_payload().

>   
> -static int dec_payload(struct snp_guest_dev *snp_dev, struct snp_guest_msg *msg,
> +static int dec_payload(struct aesgcm_ctx *ctx, struct snp_guest_msg *msg,
>   		       void *plaintext, size_t len)
>   {
> -	struct snp_guest_crypto *crypto = snp_dev->crypto;
>   	struct snp_guest_msg_hdr *hdr = &msg->hdr;
> +	u8 iv[GCM_AES_IV_SIZE] = {};
>   
> -	/* Build IV with response buffer sequence number */
> -	memset(crypto->iv, 0, crypto->iv_len);
> -	memcpy(crypto->iv, &hdr->msg_seqno, sizeof(hdr->msg_seqno));
> -
> -	return enc_dec_message(crypto, msg, msg->payload, plaintext, len, false);
> +	memcpy(iv, &hdr->msg_seqno, sizeof(hdr->msg_seqno));
> +	if (aesgcm_decrypt(ctx, plaintext, msg->payload, len, &hdr->algo,
> +			   AAD_LEN, iv, hdr->authtag))
> +		return 0;
> +	else
> +		return -EBADMSG;

This would look cleaner / read easier to me to have as:

	if (!aesgcm_decrypt(...))
		return -EBADMSG;

	return 0;

But just my opinion.

And ditto here on the size now, can probably just be part of 
verify_and_dec_payload() now.

Thanks,
Tom

>   }
>   
>   static int verify_and_dec_payload(struct snp_guest_dev *snp_dev, void *payload, u32 sz)
>   {
> -	struct snp_guest_crypto *crypto = snp_dev->crypto;
>   	struct snp_guest_msg *resp = &snp_dev->secret_response;
>   	struct snp_guest_msg *req = &snp_dev->secret_request;
>   	struct snp_guest_msg_hdr *req_hdr = &req->hdr;
>   	struct snp_guest_msg_hdr *resp_hdr = &resp->hdr;
> +	struct aesgcm_ctx *ctx = snp_dev->ctx;
>   
>   	dev_dbg(snp_dev->dev, "response [seqno %lld type %d version %d sz %d]\n",
>   		resp_hdr->msg_seqno, resp_hdr->msg_type, resp_hdr->msg_version, resp_hdr->msg_sz);
> @@ -298,11 +216,11 @@ 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);
> +	return dec_payload(ctx, resp, payload, resp_hdr->msg_sz);
>   }
>   
>   static int enc_payload(struct snp_guest_dev *snp_dev, u64 seqno, int version, u8 type,
> @@ -329,7 +247,7 @@ 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);
> +	return __enc_payload(snp_dev->ctx, req, payload, sz);
>   }
>   
>   static int __handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
> @@ -472,7 +390,6 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
>   
>   static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
>   {
> -	struct snp_guest_crypto *crypto = snp_dev->crypto;
>   	struct snp_report_resp *resp;
>   	struct snp_report_req req;
>   	int rc, resp_len;
> @@ -490,7 +407,7 @@ static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_io
>   	 * response payload. Make sure that it has enough space to cover the
>   	 * authtag.
>   	 */
> -	resp_len = sizeof(resp->data) + crypto->a_len;
> +	resp_len = sizeof(resp->data) + snp_dev->ctx->authsize;
>   	resp = kzalloc(resp_len, GFP_KERNEL_ACCOUNT);
>   	if (!resp)
>   		return -ENOMEM;
> @@ -511,7 +428,6 @@ static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_io
>   
>   static int get_derived_key(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
>   {
> -	struct snp_guest_crypto *crypto = snp_dev->crypto;
>   	struct snp_derived_key_resp resp = {0};
>   	struct snp_derived_key_req req;
>   	int rc, resp_len;
> @@ -528,7 +444,7 @@ static int get_derived_key(struct snp_guest_dev *snp_dev, struct snp_guest_reque
>   	 * response payload. Make sure that it has enough space to cover the
>   	 * authtag.
>   	 */
> -	resp_len = sizeof(resp.data) + crypto->a_len;
> +	resp_len = sizeof(resp.data) + snp_dev->ctx->authsize;
>   	if (sizeof(buf) < resp_len)
>   		return -ENOMEM;
>   
> @@ -552,7 +468,6 @@ static int get_derived_key(struct snp_guest_dev *snp_dev, struct snp_guest_reque
>   
>   static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
>   {
> -	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;
> @@ -590,7 +505,7 @@ static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_reques
>   	 * response payload. Make sure that it has enough space to cover the
>   	 * authtag.
>   	 */
> -	resp_len = sizeof(resp->data) + crypto->a_len;
> +	resp_len = sizeof(resp->data) + snp_dev->ctx->authsize;
>   	resp = kzalloc(resp_len, GFP_KERNEL_ACCOUNT);
>   	if (!resp)
>   		return -ENOMEM;
> @@ -802,8 +717,8 @@ static int __init sev_guest_probe(struct platform_device *pdev)
>   		goto e_free_response;
>   
>   	ret = -EIO;
> -	snp_dev->crypto = init_crypto(snp_dev, snp_dev->vmpck, VMPCK_KEY_LEN);
> -	if (!snp_dev->crypto)
> +	snp_dev->ctx = snp_init_crypto(snp_dev->vmpck, VMPCK_KEY_LEN);
> +	if (!snp_dev->ctx)
>   		goto e_free_cert_data;
>   
>   	misc = &snp_dev->misc;
> @@ -818,11 +733,13 @@ static int __init sev_guest_probe(struct platform_device *pdev)
>   
>   	ret =  misc_register(misc);
>   	if (ret)
> -		goto e_free_cert_data;
> +		goto e_free_ctx;
>   
>   	dev_info(dev, "Initialized SEV guest driver (using vmpck_id %d)\n", vmpck_id);
>   	return 0;
>   
> +e_free_ctx:
> +	kfree(snp_dev->ctx);
>   e_free_cert_data:
>   	free_shared_pages(snp_dev->certs_data, SEV_FW_BLOB_MAX_SIZE);
>   e_free_response:
> @@ -841,7 +758,7 @@ static int __exit sev_guest_remove(struct platform_device *pdev)
>   	free_shared_pages(snp_dev->certs_data, SEV_FW_BLOB_MAX_SIZE);
>   	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);
> +	kfree(snp_dev->ctx);
>   	misc_deregister(&snp_dev->misc);
>   
>   	return 0;
> diff --git a/drivers/virt/coco/sev-guest/sev-guest.h b/drivers/virt/coco/sev-guest/sev-guest.h
> index 21bda26fdb95..ceb798a404d6 100644
> --- a/drivers/virt/coco/sev-guest/sev-guest.h
> +++ b/drivers/virt/coco/sev-guest/sev-guest.h
> @@ -13,6 +13,9 @@
>   #include <linux/types.h>
>   
>   #define MAX_AUTHTAG_LEN		32
> +#define AUTHTAG_LEN		16
> +#define AAD_LEN			48
> +#define MSG_HDR_VER		1
>   
>   /* See SNP spec SNP_GUEST_REQUEST section for the structure */
>   enum msg_type {