Commit 970ab823 authored by Borislav Petkov (AMD)'s avatar Borislav Petkov (AMD)
Browse files

virt/coco/sev-guest: Simplify extended guest request handling 



Return a specific error code - -ENOSPC - to signal the too small cert
data buffer instead of checking exit code and exitinfo2.

While at it, hoist the *fw_err assignment in snp_issue_guest_request()
so that a proper error value is returned to the callers.

  [ Tom: check override_err instead of err. ]

Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: default avatarTom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230307192449.24732-4-bp@alien8.de
parent d6fd48ef

arch/x86/kernel/sev.c

+6 −5
Original line number Diff line number Diff line
@@ -2209,16 +2209,17 @@ int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned 
	if (ret)

		goto e_put;



	*fw_err = ghcb->save.sw_exit_info_2;

	if (ghcb->save.sw_exit_info_2) {

		/* Number of expected pages are returned in RBX */

		if (exit_code == SVM_VMGEXIT_EXT_GUEST_REQUEST &&

		    ghcb->save.sw_exit_info_2 == SNP_GUEST_REQ_INVALID_LEN)

		    ghcb->save.sw_exit_info_2 == SNP_GUEST_REQ_INVALID_LEN) {

			input->data_npages = ghcb_get_rbx(ghcb);



		*fw_err = ghcb->save.sw_exit_info_2;



			ret = -ENOSPC;

		} else {

			ret = -EIO;

		}

	}



e_put:

	__sev_put_ghcb(&state);

drivers/virt/coco/sev-guest/sev-guest.c

+26 −22
Original line number Diff line number Diff line
@@ -322,7 +322,8 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in 
				u8 type, void *req_buf, size_t req_sz, void *resp_buf,

				u32 resp_sz, __u64 *fw_err)

{

	unsigned long err;

	unsigned long err, override_err = 0;

	unsigned int override_npages = 0;

	u64 seqno;

	int rc;
@@ -338,6 +339,7 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in 
	if (rc)

		return 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
@@ -346,18 +348,25 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in 
	 */

	rc = snp_issue_guest_request(exit_code, &snp_dev->input, &err);



	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.

		 * 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.

		 */

	if (exit_code == SVM_VMGEXIT_EXT_GUEST_REQUEST &&

	    err == SNP_GUEST_REQ_INVALID_LEN) {

		const unsigned int certs_npages = snp_dev->input.data_npages;



		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_REQ_INVALID_LEN;



		/*

		 * If this call to the firmware succeeds, the sequence number can

		 * be incremented allowing for continued use of the VMPCK. If
@@ -366,15 +375,7 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in 
		 * of the VMPCK and the error code being propagated back to the

		 * user as an ioctl() return code.

		 */

		rc = snp_issue_guest_request(exit_code, &snp_dev->input, &err);



		/*

		 * Override the error to inform callers the given extended

		 * request buffer size was too small and give the caller the

		 * required buffer size.

		 */

		err = SNP_GUEST_REQ_INVALID_LEN;

		snp_dev->input.data_npages = certs_npages;

		goto retry_request;

	}



	/*
@@ -386,7 +387,10 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in 
	snp_inc_msg_seqno(snp_dev);



	if (fw_err)

		*fw_err = err;

		*fw_err = override_err ?: err;



	if (override_npages)

		snp_dev->input.data_npages = override_npages;



	/*

	 * If an extended guest request was issued and the supplied certificate
@@ -394,7 +398,7 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in 
	 * prevent IV reuse. If the standard request was successful, return -EIO

	 * back to the caller as would have originally been returned.

	 */

	if (!rc && err == SNP_GUEST_REQ_INVALID_LEN)

	if (!rc && override_err == SNP_GUEST_REQ_INVALID_LEN)

		return -EIO;



	if (rc) {