summaryrefslogtreecommitdiffstats
path: root/drivers/virt/coco/sev-guest/sev-guest.c
blob: c47e54b2a865eaa8f4a9be223540a190989d4448 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
// SPDX-License-Identifier: GPL-2.0-only
/*
 * AMD Secure Encrypted Virtualization (SEV) guest driver interface
 *
 * Copyright (C) 2021 Advanced Micro Devices, Inc.
 *
 * Author: Brijesh Singh <brijesh.singh@amd.com>
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/mutex.h>
#include <linux/io.h>
#include <linux/platform_device.h>
#include <linux/miscdevice.h>
#include <linux/set_memory.h>
#include <linux/fs.h>
#include <crypto/aead.h>
#include <linux/scatterlist.h>
#include <linux/psp-sev.h>
#include <uapi/linux/sev-guest.h>
#include <uapi/linux/psp-sev.h>

#include <asm/svm.h>
#include <asm/sev.h>

#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;
	/* request and response are in unencrypted memory */
	struct snp_guest_msg *request, *response;

	/*
	 * Avoid information leakage by double-buffering shared messages
	 * in fields that are in regular encrypted memory.
	 */
	struct snp_guest_msg secret_request, secret_response;

	struct snp_secrets_page_layout *layout;
	struct snp_req_data input;
	union {
		struct snp_report_req report;
		struct snp_derived_key_req derived_key;
		struct snp_ext_report_req ext_report;
	} req;
	u32 *os_area_msg_seqno;
	u8 *vmpck;
};

static u32 vmpck_id;
module_param(vmpck_id, uint, 0444);
MODULE_PARM_DESC(vmpck_id, "The VMPCK ID to use when communicating with the PSP.");

/* Mutex to serialize the shared buffer access and command handling. */
static DEFINE_MUTEX(snp_cmd_mutex);

static bool is_vmpck_empty(struct snp_guest_dev *snp_dev)
{
	char zero_key[VMPCK_KEY_LEN] = {0};

	if (snp_dev->vmpck)
		return !memcmp(snp_dev->vmpck, zero_key, VMPCK_KEY_LEN);

	return true;
}

/*
 * If an error is received from the host or AMD Secure Processor (ASP) there
 * are two options. Either retry the exact same encrypted request or 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 the sequence number were to be reused the encryption scheme is
 * vulnerable. If the sequence number were incremented for a fresh IV the ASP
 * will reject the 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;
}

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

	lockdep_assert_held(&snp_cmd_mutex);

	/* Read the current message sequence counter from secrets pages */
	count = *snp_dev->os_area_msg_seqno;

	return count + 1;
}

/* Return a non-zero on success */
static u64 snp_get_msg_seqno(struct snp_guest_dev *snp_dev)
{
	u64 count = __snp_get_msg_seqno(snp_dev);

	/*
	 * The message sequence counter for the SNP guest request is a  64-bit
	 * value but the version 2 of GHCB specification defines a 32-bit storage
	 * for it. If the counter exceeds the 32-bit value then return zero.
	 * The caller should check the return value, but if the caller happens to
	 * not check the value and use it, then the firmware treats zero as an
	 * invalid number and will fail the  message request.
	 */
	if (count >= UINT_MAX) {
		dev_err(snp_dev->dev, "request message sequence counter overflow\n");
		return 0;
	}

	return count;
}

static void snp_inc_msg_seqno(struct snp_guest_dev *snp_dev)
{
	/*
	 * The counter is also incremented by the PSP, so increment it by 2
	 * and save in secrets page.
	 */
	*snp_dev->os_area_msg_seqno += 2;
}

static inline struct snp_guest_dev *to_snp_dev(struct file *file)
{
	struct miscdevice *dev = file->private_data;

	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)
{
	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;

	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;
		}
	}

	crypto->a_len = crypto_aead_authsize(crypto->tfm);
	crypto->authtag = kmalloc(crypto->a_len, GFP_KERNEL_ACCOUNT);
	if (!crypto->authtag)
		goto e_free_auth;

	return crypto;

e_free_auth:
	kfree(crypto->authtag);
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;
}

static int __enc_payload(struct snp_guest_dev *snp_dev, 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;

	memset(crypto->iv, 0, crypto->iv_len);
	memcpy(crypto->iv, &hdr->msg_seqno, sizeof(hdr->msg_seqno));

	return enc_dec_message(crypto, msg, plaintext, msg->payload, len, true);
}

static int dec_payload(struct snp_guest_dev *snp_dev, 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;

	/* 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);
}

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;

	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);

	/* Copy response from shared memory to encrypted memory. */
	memcpy(resp, snp_dev->response, sizeof(*resp));

	/* Verify that the sequence counter is incremented by 1 */
	if (unlikely(resp_hdr->msg_seqno != (req_hdr->msg_seqno + 1)))
		return -EBADMSG;

	/* Verify response message type and version number. */
	if (resp_hdr->msg_type != (req_hdr->msg_type + 1) ||
	    resp_hdr->msg_version != req_hdr->msg_version)
		return -EBADMSG;

	/*
	 * If the message size is greater than our buffer length then return
	 * an error.
	 */
	if (unlikely((resp_hdr->msg_sz + crypto->a_len) > sz))
		return -EBADMSG;

	/* Decrypt the payload */
	return dec_payload(snp_dev, resp, payload, resp_hdr->msg_sz + crypto->a_len);
}

static int enc_payload(struct snp_guest_dev *snp_dev, u64 seqno, int version, u8 type,
			void *payload, size_t sz)
{
	struct snp_guest_msg *req = &snp_dev->secret_request;
	struct snp_guest_msg_hdr *hdr = &req->hdr;

	memset(req, 0, sizeof(*req));

	hdr->algo = SNP_AEAD_AES_256_GCM;
	hdr->hdr_version = MSG_HDR_VER;
	hdr->hdr_sz = sizeof(*hdr);
	hdr->msg_type = type;
	hdr->msg_version = version;
	hdr->msg_seqno = seqno;
	hdr->msg_vmpck = vmpck_id;
	hdr->msg_sz = sz;

	/* Verify the sequence number is non-zero */
	if (!hdr->msg_seqno)
		return -ENOSR;

	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);
}

static int __handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
				  struct snp_guest_request_ioctl *rio)
{
	unsigned long req_start = jiffies;
	unsigned int override_npages = 0;
	u64 override_err = 0;
	int rc;

retry_request:
	/*
	 * Call firmware to process the request. In this function the encrypted
	 * message enters shared memory with the host. So after this call the
	 * sequence number must be incremented or the VMPCK must be deleted to
	 * prevent reuse of the IV.
	 */
	rc = snp_issue_guest_request(exit_code, &snp_dev->input, rio);
	switch (rc) {
	case -ENOSPC:
		/*
		 * If the extended guest request fails due to having too
		 * small of a certificate data buffer, retry the same
		 * guest request without the extended data request in
		 * order to increment the sequence number and thus avoid
		 * IV reuse.
		 */
		override_npages = snp_dev->input.data_npages;
		exit_code	= SVM_VMGEXIT_GUEST_REQUEST;

		/*
		 * Override the error to inform callers the given extended
		 * request buffer size was too small and give the caller the
		 * required buffer size.
		 */
		override_err = SNP_GUEST_VMM_ERR(SNP_GUEST_VMM_ERR_INVALID_LEN);

		/*
		 * If this call to the firmware succeeds, the sequence number can
		 * be incremented allowing for continued use of the VMPCK. If
		 * there is an error reflected in the return value, this value
		 * is checked further down and the result will be the deletion
		 * of the VMPCK and the error code being propagated back to the
		 * user as an ioctl() return code.
		 */
		goto retry_request;

	/*
	 * The host may return SNP_GUEST_VMM_ERR_BUSY if the request has been
	 * throttled. Retry in the driver to avoid returning and reusing the
	 * message sequence number on a different message.
	 */
	case -EAGAIN:
		if (jiffies - req_start > SNP_REQ_MAX_RETRY_DURATION) {
			rc = -ETIMEDOUT;
			break;
		}
		schedule_timeout_killable(SNP_REQ_RETRY_DELAY);
		goto retry_request;
	}

	/*
	 * Increment the message sequence number. There is no harm in doing
	 * this now because decryption uses the value stored in the response
	 * structure and any failure will wipe the VMPCK, preventing further
	 * use anyway.
	 */
	snp_inc_msg_seqno(snp_dev);

	if (override_err) {
		rio->exitinfo2 = override_err;

		/*
		 * If an extended guest request was issued and the supplied certificate
		 * buffer was not large enough, a standard guest request was issued to
		 * prevent IV reuse. If the standard request was successful, return -EIO
		 * back to the caller as would have originally been returned.
		 */
		if (!rc && override_err == SNP_GUEST_VMM_ERR(SNP_GUEST_VMM_ERR_INVALID_LEN))
			rc = -EIO;
	}

	if (override_npages)
		snp_dev->input.data_npages = override_npages;

	return rc;
}

static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
				struct snp_guest_request_ioctl *rio, u8 type,
				void *req_buf, size_t req_sz, void *resp_buf,
				u32 resp_sz)
{
	u64 seqno;
	int rc;

	/* Get message sequence and verify that its a non-zero */
	seqno = snp_get_msg_seqno(snp_dev);
	if (!seqno)
		return -EIO;

	/* Clear shared memory's response for the host to populate. */
	memset(snp_dev->response, 0, sizeof(struct snp_guest_msg));

	/* Encrypt the userspace provided payload in snp_dev->secret_request. */
	rc = enc_payload(snp_dev, seqno, rio->msg_version, type, req_buf, req_sz);
	if (rc)
		return rc;

	/*
	 * Write the fully encrypted request to the shared unencrypted
	 * request page.
	 */
	memcpy(snp_dev->request, &snp_dev->secret_request,
	       sizeof(snp_dev->secret_request));

	rc = __handle_guest_request(snp_dev, exit_code, rio);
	if (rc) {
		if (rc == -EIO &&
		    rio->exitinfo2 == SNP_GUEST_VMM_ERR(SNP_GUEST_VMM_ERR_INVALID_LEN))
			return rc;

		dev_alert(snp_dev->dev,
			  "Detected error from ASP request. rc: %d, exitinfo2: 0x%llx\n",
			  rc, rio->exitinfo2);

		snp_disable_vmpck(snp_dev);
		return rc;
	}

	rc = verify_and_dec_payload(snp_dev, resp_buf, resp_sz);
	if (rc) {
		dev_alert(snp_dev->dev, "Detected unexpected decode failure from ASP. rc: %d\n", rc);
		snp_disable_vmpck(snp_dev);
		return rc;
	}

	return 0;
}

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_req *req = &snp_dev->req.report;
	struct snp_report_resp *resp;
	int rc, resp_len;

	lockdep_assert_held(&snp_cmd_mutex);

	if (!arg->req_data || !arg->resp_data)
		return -EINVAL;

	if (copy_from_user(req, (void __user *)arg->req_data, sizeof(*req)))
		return -EFAULT;

	/*
	 * The intermediate response buffer is used while decrypting the
	 * response payload. Make sure that it has enough space to cover the
	 * authtag.
	 */
	resp_len = sizeof(resp->data) + crypto->a_len;
	resp = kzalloc(resp_len, GFP_KERNEL_ACCOUNT);
	if (!resp)
		return -ENOMEM;

	rc = handle_guest_request(snp_dev, SVM_VMGEXIT_GUEST_REQUEST, arg,
				  SNP_MSG_REPORT_REQ, req, sizeof(*req), resp->data,
				  resp_len);
	if (rc)
		goto e_free;

	if (copy_to_user((void __user *)arg->resp_data, resp, sizeof(*resp)))
		rc = -EFAULT;

e_free:
	kfree(resp);
	return rc;
}

static int get_derived_key(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
{
	struct snp_derived_key_req *req = &snp_dev->req.derived_key;
	struct snp_guest_crypto *crypto = snp_dev->crypto;
	struct snp_derived_key_resp resp = {0};
	int rc, resp_len;
	/* Response data is 64 bytes and max authsize for GCM is 16 bytes. */
	u8 buf[64 + 16];

	lockdep_assert_held(&snp_cmd_mutex);

	if (!arg->req_data || !arg->resp_data)
		return -EINVAL;

	/*
	 * The intermediate response buffer is used while decrypting the
	 * response payload. Make sure that it has enough space to cover the
	 * authtag.
	 */
	resp_len = sizeof(resp.data) + crypto->a_len;
	if (sizeof(buf) < resp_len)
		return -ENOMEM;

	if (copy_from_user(req, (void __user *)arg->req_data, sizeof(*req)))
		return -EFAULT;

	rc = handle_guest_request(snp_dev, SVM_VMGEXIT_GUEST_REQUEST, arg,
				  SNP_MSG_KEY_REQ, req, sizeof(*req), buf, resp_len);
	if (rc)
		return rc;

	memcpy(resp.data, buf, sizeof(resp.data));
	if (copy_to_user((void __user *)arg->resp_data, &resp, sizeof(resp)))
		rc = -EFAULT;

	/* The response buffer contains the sensitive data, explicitly clear it. */
	memzero_explicit(buf, sizeof(buf));
	memzero_explicit(&resp, sizeof(resp));
	return rc;
}

static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
{
	struct snp_ext_report_req *req = &snp_dev->req.ext_report;
	struct snp_guest_crypto *crypto = snp_dev->crypto;
	struct snp_report_resp *resp;
	int ret, npages = 0, resp_len;

	lockdep_assert_held(&snp_cmd_mutex);

	if (!arg->req_data || !arg->resp_data)
		return -EINVAL;

	if (copy_from_user(req, (void __user *)arg->req_data, sizeof(*req)))
		return -EFAULT;

	/* userspace does not want certificate data */
	if (!req->certs_len || !req->certs_address)
		goto cmd;

	if (req->certs_len > SEV_FW_BLOB_MAX_SIZE ||
	    !IS_ALIGNED(req->certs_len, PAGE_SIZE))
		return -EINVAL;

	if (!access_ok((const void __user *)req->certs_address, req->certs_len))
		return -EFAULT;

	/*
	 * Initialize the intermediate buffer with all zeros. This buffer
	 * is used in the guest request message to get the certs blob from
	 * 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;
cmd:
	/*
	 * The intermediate response buffer is used while decrypting the
	 * response payload. Make sure that it has enough space to cover the
	 * authtag.
	 */
	resp_len = sizeof(resp->data) + crypto->a_len;
	resp = kzalloc(resp_len, GFP_KERNEL_ACCOUNT);
	if (!resp)
		return -ENOMEM;

	snp_dev->input.data_npages = npages;
	ret = handle_guest_request(snp_dev, SVM_VMGEXIT_EXT_GUEST_REQUEST, arg,
				   SNP_MSG_REPORT_REQ, &req->data,
				   sizeof(req->data), resp->data, resp_len);

	/* If certs length is invalid then copy the returned length */
	if (arg->vmm_error == SNP_GUEST_VMM_ERR_INVALID_LEN) {
		req->certs_len = snp_dev->input.data_npages << PAGE_SHIFT;

		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)) {
		ret = -EFAULT;
		goto e_free;
	}

	if (copy_to_user((void __user *)arg->resp_data, resp, sizeof(*resp)))
		ret = -EFAULT;

e_free:
	kfree(resp);
	return ret;
}

static long snp_guest_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
{
	struct snp_guest_dev *snp_dev = to_snp_dev(file);
	void __user *argp = (void __user *)arg;
	struct snp_guest_request_ioctl input;
	int ret = -ENOTTY;

	if (copy_from_user(&input, argp, sizeof(input)))
		return -EFAULT;

	input.exitinfo2 = 0xff;

	/* Message version must be non-zero */
	if (!input.msg_version)
		return -EINVAL;

	mutex_lock(&snp_cmd_mutex);

	/* Check if the VMPCK is not empty */
	if (is_vmpck_empty(snp_dev)) {
		dev_err_ratelimited(snp_dev->dev, "VMPCK is disabled\n");
		mutex_unlock(&snp_cmd_mutex);
		return -ENOTTY;
	}

	switch (ioctl) {
	case SNP_GET_REPORT:
		ret = get_report(snp_dev, &input);
		break;
	case SNP_GET_DERIVED_KEY:
		ret = get_derived_key(snp_dev, &input);
		break;
	case SNP_GET_EXT_REPORT:
		ret = get_ext_report(snp_dev, &input);
		break;
	default:
		break;
	}

	mutex_unlock(&snp_cmd_mutex);

	if (input.exitinfo2 && copy_to_user(argp, &input, sizeof(input)))
		return -EFAULT;

	return ret;
}

static void free_shared_pages(void *buf, size_t sz)
{
	unsigned int npages = PAGE_ALIGN(sz) >> PAGE_SHIFT;
	int ret;

	if (!buf)
		return;

	ret = set_memory_encrypted((unsigned long)buf, npages);
	if (ret) {
		WARN_ONCE(ret, "failed to restore encryption mask (leak it)\n");
		return;
	}

	__free_pages(virt_to_page(buf), get_order(sz));
}

static void *alloc_shared_pages(struct device *dev, size_t sz)
{
	unsigned int npages = PAGE_ALIGN(sz) >> PAGE_SHIFT;
	struct page *page;
	int ret;

	page = alloc_pages(GFP_KERNEL_ACCOUNT, get_order(sz));
	if (!page)
		return NULL;

	ret = set_memory_decrypted((unsigned long)page_address(page), npages);
	if (ret) {
		dev_err(dev, "failed to mark page shared, ret=%d\n", ret);
		__free_pages(page, get_order(sz));
		return NULL;
	}

	return page_address(page);
}

static const struct file_operations snp_guest_fops = {
	.owner	= THIS_MODULE,
	.unlocked_ioctl = snp_guest_ioctl,
};

static u8 *get_vmpck(int id, struct snp_secrets_page_layout *layout, u32 **seqno)
{
	u8 *key = NULL;

	switch (id) {
	case 0:
		*seqno = &layout->os_area.msg_seqno_0;
		key = layout->vmpck0;
		break;
	case 1:
		*seqno = &layout->os_area.msg_seqno_1;
		key = layout->vmpck1;
		break;
	case 2:
		*seqno = &layout->os_area.msg_seqno_2;
		key = layout->vmpck2;
		break;
	case 3:
		*seqno = &layout->os_area.msg_seqno_3;
		key = layout->vmpck3;
		break;
	default:
		break;
	}

	return key;
}

static int __init sev_guest_probe(struct platform_device *pdev)
{
	struct snp_secrets_page_layout *layout;
	struct sev_guest_platform_data *data;
	struct device *dev = &pdev->dev;
	struct snp_guest_dev *snp_dev;
	struct miscdevice *misc;
	void __iomem *mapping;
	int ret;

	if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
		return -ENODEV;

	if (!dev->platform_data)
		return -ENODEV;

	data = (struct sev_guest_platform_data *)dev->platform_data;
	mapping = ioremap_encrypted(data->secrets_gpa, PAGE_SIZE);
	if (!mapping)
		return -ENODEV;

	layout = (__force void *)mapping;

	ret = -ENOMEM;
	snp_dev = devm_kzalloc(&pdev->dev, sizeof(struct snp_guest_dev), GFP_KERNEL);
	if (!snp_dev)
		goto e_unmap;

	ret = -EINVAL;
	snp_dev->vmpck = get_vmpck(vmpck_id, layout, &snp_dev->os_area_msg_seqno);
	if (!snp_dev->vmpck) {
		dev_err(dev, "invalid vmpck id %d\n", vmpck_id);
		goto e_unmap;
	}

	/* Verify that VMPCK is not zero. */
	if (is_vmpck_empty(snp_dev)) {
		dev_err(dev, "vmpck id %d is null\n", vmpck_id);
		goto e_unmap;
	}

	platform_set_drvdata(pdev, snp_dev);
	snp_dev->dev = dev;
	snp_dev->layout = layout;

	/* Allocate the shared page used for the request and response message. */
	snp_dev->request = alloc_shared_pages(dev, sizeof(struct snp_guest_msg));
	if (!snp_dev->request)
		goto e_unmap;

	snp_dev->response = alloc_shared_pages(dev, sizeof(struct snp_guest_msg));
	if (!snp_dev->response)
		goto e_free_request;

	snp_dev->certs_data = alloc_shared_pages(dev, SEV_FW_BLOB_MAX_SIZE);
	if (!snp_dev->certs_data)
		goto e_free_response;

	ret = -EIO;
	snp_dev->crypto = init_crypto(snp_dev, snp_dev->vmpck, VMPCK_KEY_LEN);
	if (!snp_dev->crypto)
		goto e_free_cert_data;

	misc = &snp_dev->misc;
	misc->minor = MISC_DYNAMIC_MINOR;
	misc->name = DEVICE_NAME;
	misc->fops = &snp_guest_fops;

	/* initial the input address for guest request */
	snp_dev->input.req_gpa = __pa(snp_dev->request);
	snp_dev->input.resp_gpa = __pa(snp_dev->response);
	snp_dev->input.data_gpa = __pa(snp_dev->certs_data);

	ret =  misc_register(misc);
	if (ret)
		goto e_free_cert_data;

	dev_info(dev, "Initialized SEV guest driver (using vmpck_id %d)\n", vmpck_id);
	return 0;

e_free_cert_data:
	free_shared_pages(snp_dev->certs_data, SEV_FW_BLOB_MAX_SIZE);
e_free_response:
	free_shared_pages(snp_dev->response, sizeof(struct snp_guest_msg));
e_free_request:
	free_shared_pages(snp_dev->request, sizeof(struct snp_guest_msg));
e_unmap:
	iounmap(mapping);
	return ret;
}

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->response, sizeof(struct snp_guest_msg));
	free_shared_pages(snp_dev->request, sizeof(struct snp_guest_msg));
	deinit_crypto(snp_dev->crypto);
	misc_deregister(&snp_dev->misc);

	return 0;
}

/*
 * This driver is meant to be a common SEV guest interface driver and to
 * support any SEV guest API. As such, even though it has been introduced
 * with the SEV-SNP support, it is named "sev-guest".
 */
static struct platform_driver sev_guest_driver = {
	.remove		= __exit_p(sev_guest_remove),
	.driver		= {
		.name = "sev-guest",
	},
};

module_platform_driver_probe(sev_guest_driver, sev_guest_probe);

MODULE_AUTHOR("Brijesh Singh <brijesh.singh@amd.com>");
MODULE_LICENSE("GPL");
MODULE_VERSION("1.0.0");
MODULE_DESCRIPTION("AMD SEV Guest Driver");
MODULE_ALIAS("platform:sev-guest");