lkml.org 
[lkml]   [2023]   [Feb]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [RESEND PATCH] virt/sev-guest: Return -EIO if certificate buffer is not large enough
From
On 2/22/23 10:51, Peter Gonda wrote:
> On Wed, Feb 22, 2023 at 9:39 AM Tom Lendacky <thomas.lendacky@amd.com> wrote:
>>
>> 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 return value of -EIO was returned. Now a return value of 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@amd.com>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>
> My bad. I wasn't testing the return value in this case.
>
> Should Boris take this patch into the retry series?
>
>> ---
>> drivers/virt/coco/sev-guest/sev-guest.c | 20 +++++++++++++++++---
>> 1 file changed, 17 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
>> index 4ec4174e05a3..7b4e9009f335 100644
>> --- a/drivers/virt/coco/sev-guest/sev-guest.c
>> +++ b/drivers/virt/coco/sev-guest/sev-guest.c
>> @@ -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;
>> +
>
> Why not set 'ret = -EIO' and use disable_vmpck directly? That seems
> more clear to me instead of failing on the next call.

We don't want to disable the VMPCK for this. This should go back to
userspace with EIO and SNP_GUEST_REQ_INVALID_LEN, as it did prior to
47894e0fa6a5. Userspace then allocates a larger buffer and re-issues the
request which should now succeed.

Thanks,
Tom

>
>> 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:
>> --
>> 2.39.1
>>

\
 
 \ /
  Last update: 2023-03-27 00:33    [W:0.059 / U:2.812 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site