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virt/coco/sev-guest: Simplify extended guest request handling 

Return a specific error code - -ENOSPC - to signal the too small cert
data buffer instead of checking exit code and exitinfo2.

While at it, hoist the *fw_err assignment in snp_issue_guest_request()
so that a proper error value is returned to the callers.

  [ Tom: check override_err instead of err. ]

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230307192449.24732-4-bp@alien8.de
This commit is contained in:
Borislav Petkov (AMD) 2023-02-15 11:39:41 +01:00
parent d6fd48eff7
commit 970ab82374
2 changed files with 32 additions and 27 deletions
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11
arch/x86/kernel/sev.c
View File

@ -2209,15 +2209,16 @@ int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned
if (ret)
goto e_put;
*fw_err = ghcb->save.sw_exit_info_2;
if (ghcb->save.sw_exit_info_2) {
/* Number of expected pages are returned in RBX */
if (exit_code == SVM_VMGEXIT_EXT_GUEST_REQUEST &&
ghcb->save.sw_exit_info_2 == SNP_GUEST_REQ_INVALID_LEN)
ghcb->save.sw_exit_info_2 == SNP_GUEST_REQ_INVALID_LEN) {
input->data_npages = ghcb_get_rbx(ghcb);
*fw_err = ghcb->save.sw_exit_info_2;
ret = -EIO;
ret = -ENOSPC;
} else {
ret = -EIO;
}
}
e_put:

48
drivers/virt/coco/sev-guest/sev-guest.c
View File

@ -322,7 +322,8 @@ 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;
unsigned long err, override_err = 0;
unsigned int override_npages = 0;
u64 seqno;
int rc;
@ -338,6 +339,7 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
if (rc)
return rc;
retry_request:
/*
* Call firmware to process the request. In this function the encrypted
* message enters shared memory with the host. So after this call the
@ -346,17 +348,24 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
*/
rc = snp_issue_guest_request(exit_code, &snp_dev->input, &err);
/*
* If the extended guest request fails due to having too small of a
* certificate data buffer, retry the same guest request without the
* extended data request in order to increment the sequence number
* and thus avoid IV reuse.
*/
if (exit_code == SVM_VMGEXIT_EXT_GUEST_REQUEST &&
err == SNP_GUEST_REQ_INVALID_LEN) {
const unsigned int certs_npages = snp_dev->input.data_npages;
switch (rc) {
case -ENOSPC:
/*
* If the extended guest request fails due to having too
* small of a certificate data buffer, retry the same
* guest request without the extended data request in
* order to increment the sequence number and thus avoid
* IV reuse.
*/
override_npages = snp_dev->input.data_npages;
exit_code = SVM_VMGEXIT_GUEST_REQUEST;
exit_code = SVM_VMGEXIT_GUEST_REQUEST;
/*
* Override the error to inform callers the given extended
* request buffer size was too small and give the caller the
* required buffer size.
*/
override_err = SNP_GUEST_REQ_INVALID_LEN;
/*
* If this call to the firmware succeeds, the sequence number can
@ -366,15 +375,7 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
* of the VMPCK and the error code being propagated back to the
* user as an ioctl() return code.
*/
rc = snp_issue_guest_request(exit_code, &snp_dev->input, &err);
/*
* Override the error to inform callers the given extended
* request buffer size was too small and give the caller the
* required buffer size.
*/
err = SNP_GUEST_REQ_INVALID_LEN;
snp_dev->input.data_npages = certs_npages;
goto retry_request;
}
/*
@ -386,7 +387,10 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
snp_inc_msg_seqno(snp_dev);
if (fw_err)
*fw_err = err;
*fw_err = override_err ?: err;
if (override_npages)
snp_dev->input.data_npages = override_npages;
/*
* If an extended guest request was issued and the supplied certificate
@ -394,7 +398,7 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
* 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)
if (!rc && override_err == SNP_GUEST_REQ_INVALID_LEN)
return -EIO;
if (rc) {