[PATCH v7 3/4] virt: sev-guest: Remove err in handle_guest_request

[Dionna Glaze <dionnaglaze@google.com>]

The err variable may not be set in the call to snp_issue_guest_request,
yet it is unconditionally written back to fw_err if fw_err is non-null.
This is undefined behavior, and currently returns uninitialized kernel
stack memory to user space.

The fw_err argument is better to just pass through to
snp_issue_guest_request, so we do that. Since the issue_request's
signature has changed fw_err to exitinfo2, we change the argument name
here.

Cc: Tom Lendacky <Thomas.Lendacky@amd.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Joerg Roedel <jroedel@suse.de>
Cc: Peter Gonda <pgonda@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Haowen Bai <baihaowen@meizu.com>
Cc: Liam Merwick <liam.merwick@oracle.com>
Cc: Yang Yingliang <yangyingliang@huawei.com>

Fixes: fce96cf04430 ("virt: Add SEV-SNP guest driver")
Signed-off-by: Dionna Glaze <dionnaglaze@google.com>
---
 drivers/virt/coco/sev-guest/sev-guest.c | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
index d08ff87c2dac..5ebf87651299 100644
--- a/drivers/virt/coco/sev-guest/sev-guest.c
+++ b/drivers/virt/coco/sev-guest/sev-guest.c
@@ -322,9 +322,8 @@ static int enc_payload(struct snp_guest_dev *snp_dev, u64 seqno, int version, u8
 
 static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, int msg_ver,
 				u8 type, void *req_buf, size_t req_sz, void *resp_buf,
-				u32 resp_sz, __u64 *fw_err)
+				u32 resp_sz, __u64 *exitinfo2)
 {
-	unsigned long err;
 	u64 seqno;
 	int rc;
 
@@ -341,7 +340,7 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
 		return rc;
 
 	/* Call firmware to process the request */
-	rc = snp_issue_guest_request(exit_code, &snp_dev->input, &err);
+	rc = snp_issue_guest_request(exit_code, &snp_dev->input, exitinfo2);
 
 	/*
 	 * If the extended guest request fails due to having to small of a
@@ -349,19 +348,16 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
 	 * extended data request.
 	 */
 	if (exit_code == SVM_VMGEXIT_EXT_GUEST_REQUEST &&
-		err == SNP_GUEST_REQ_INVALID_LEN) {
+		*exitinfo2 == SNP_GUEST_REQ_INVALID_LEN) {
 		const unsigned int certs_npages = snp_dev->input.data_npages;
 
 		exit_code = SVM_VMGEXIT_GUEST_REQUEST;
-		rc = snp_issue_guest_request(exit_code, &snp_dev->input, &err);
+		rc = snp_issue_guest_request(exit_code, &snp_dev->input, exitinfo2);
 
-		err = SNP_GUEST_REQ_INVALID_LEN;
+		*exitinfo2 = SNP_GUEST_REQ_INVALID_LEN;
 		snp_dev->input.data_npages = certs_npages;
 	}
 
-	if (fw_err)
-		*fw_err = err;
-
 	if (rc) {
 		dev_alert(snp_dev->dev,
 			  "Detected error from ASP request. rc: %d, fw_err: %llu\n",
-- 
2.38.1.431.g37b22c650d-goog