From: Tom Lendacky <thomas.lendacky@xxxxxxx>
commit dd093fb08e8f8a958fec4eef36f9f09eac047f60 upstream.
Commit
47894e0fa6a5 ("virt/sev-guest: Prevent IV reuse in the SNP guest driver")
changed the behavior associated with the return value when the caller
does not supply a large enough certificate buffer. Prior to the commit a
value of -EIO was returned. Now, 0 is returned. This breaks the
established ABI with the user.
Change the code to detect the buffer size error and return -EIO.
Fixes: 47894e0fa6a5 ("virt/sev-guest: Prevent IV reuse in the SNP guest driver")
Reported-by: Larry Dewey <larry.dewey@xxxxxxx>
Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Tested-by: Larry Dewey <larry.dewey@xxxxxxx>
Cc: <stable@xxxxxxxxxx>
Link: https://lore.kernel.org/r/2afbcae6daf13f7ad5a4296692e0a0fe1bc1e4ee.1677083979.git.thomas.lendacky@xxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/virt/coco/sev-guest/sev-guest.c | 20 +++++++++++++++++---
1 file changed, 17 insertions(+), 3 deletions(-)
--- a/drivers/virt/coco/sev-guest/sev-guest.c
+++ b/drivers/virt/coco/sev-guest/sev-guest.c
@@ -379,9 +379,26 @@ static int handle_guest_request(struct s
snp_dev->input.data_npages = certs_npages;
}
+ /*
+ * 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 (fw_err)
*fw_err = 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 && err == SNP_GUEST_REQ_INVALID_LEN)
+ return -EIO;
+
if (rc) {
dev_alert(snp_dev->dev,
"Detected error from ASP request. rc: %d, fw_err: %llu\n",
@@ -397,9 +414,6 @@ static int handle_guest_request(struct s
goto disable_vmpck;
}
- /* Increment to new message sequence after payload decryption was successful. */
- snp_inc_msg_seqno(snp_dev);
-
return 0;
disable_vmpck:
