linux-kernel - [PATCH v2] virt/coco/sev-guest: Remove err in handle_guest

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Message-ID: <20221019195815.1298915-1-dionnaglaze@google.com>
Date:   Wed, 19 Oct 2022 19:58:15 +0000
From:   Dionna Glaze <dionnaglaze@...gle.com>
To:     x86@...nel.org, linux-kernel@...r.kernel.org
Cc:     Dionna Glaze <dionnaglaze@...gle.com>,
        Tom Lendacky <Thomas.Lendacky@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Joerg Roedel <jroedel@...e.de>,
        Peter Gonda <pgonda@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: [PATCH v2] virt/coco/sev-guest: Remove err in handle_guest_request

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.

Cc: Tom Lendacky <Thomas.Lendacky@....com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Joerg Roedel <jroedel@...e.de>
Cc: Peter Gonda <pgonda@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>

Signed-off-by: Dionna Glaze <dionnaglaze@...gle.com>
---
 drivers/virt/coco/sev-guest/sev-guest.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
index f422f9c58ba7..00708b4491e0 100644
--- a/drivers/virt/coco/sev-guest/sev-guest.c
+++ b/drivers/virt/coco/sev-guest/sev-guest.c
@@ -305,7 +305,6 @@ 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;
 	u64 seqno;
 	int rc;
 
@@ -322,9 +321,7 @@ 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);
-	if (fw_err)
-		*fw_err = err;
+	rc = snp_issue_guest_request(exit_code, &snp_dev->input, fw_err);
 
 	if (rc)
 		return rc;
-- 
2.38.0.413.g74048e4d9e-goog