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virt/sev-guest: Return -EIO if certificate buffer is not large enough

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  47894e0fa6 ("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: 47894e0fa6 ("virt/sev-guest: Prevent IV reuse in the SNP guest driver")
Reported-by: Larry Dewey <larry.dewey@amd.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Larry Dewey <larry.dewey@amd.com>
Cc: <stable@kernel.org>
Link: https://lore.kernel.org/r/2afbcae6daf13f7ad5a4296692e0a0fe1bc1e4ee.1677083979.git.thomas.lendacky@amd.com
This commit is contained in:
Tom Lendacky 2023-02-22 10:39:39 -06:00 committed by Borislav Petkov (AMD)
parent e02b50ca44
commit dd093fb08e
1 changed files with 17 additions and 3 deletions
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20
drivers/virt/coco/sev-guest/sev-guest.c
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@ -377,9 +377,26 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
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",
@ -395,9 +412,6 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
goto disable_vmpck;
}
/* Increment to new message sequence after payload decryption was successful. */
snp_inc_msg_seqno(snp_dev);
return 0;
disable_vmpck: