[PATCH v10 27/27] backends/tpm: Propagate vTPM error on migration failure

[Arun Menon <armenon@redhat.com>]

- When migration of a VM with encrypted vTPM fails on the
  destination host, (e.g., due to a mismatch in secret values),
  the error message displayed on the source host is generic and unhelpful.
- For example, a typical error looks like this:
  "operation failed: job 'migration out' failed: Sibling indicated error 1.
  operation failed: job 'migration in' failed: load of migration failed:
  Input/output error"
- Such generic errors are logged using error_report(), which prints to
  the console/monitor but does not make the detailed error accessible via
  the QMP query-migrate command.
- This change, along with the set of changes of passing errp Error object
  to the VM state loading functions, help in addressing the issue.
  We use the post_load_errp hook of VMStateDescription to propagate errors
  by setting Error **errp objects in case of failure in the TPM backend.
- It can then be retrieved using QMP command:
  {"execute" : "query-migrate"}

Buglink: https://issues.redhat.com/browse/RHEL-82826

Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Arun Menon <armenon@redhat.com>
---
 backends/tpm/tpm_emulator.c | 40 +++++++++++++++++++++-------------------
 1 file changed, 21 insertions(+), 19 deletions(-)

diff --git a/backends/tpm/tpm_emulator.c b/backends/tpm/tpm_emulator.c
index 4a234ab2c0b19b2604bf0dd8cb5f4540c72a9438..dacfca5ab7eb0445ddc1ced97513068501b468bf 100644
--- a/backends/tpm/tpm_emulator.c
+++ b/backends/tpm/tpm_emulator.c
@@ -819,7 +819,8 @@ static int tpm_emulator_get_state_blobs(TPMEmulator *tpm_emu)
 static int tpm_emulator_set_state_blob(TPMEmulator *tpm_emu,
                                        uint32_t type,
                                        TPMSizedBuffer *tsb,
-                                       uint32_t flags)
+                                       uint32_t flags,
+                                       Error **errp)
 {
     ssize_t n;
     ptm_setstate pss;
@@ -838,17 +839,18 @@ static int tpm_emulator_set_state_blob(TPMEmulator *tpm_emu,
     /* write the header only */
     if (tpm_emulator_ctrlcmd(tpm_emu, CMD_SET_STATEBLOB, &pss,
                              offsetof(ptm_setstate, u.req.data), 0, 0) < 0) {
-        error_report("tpm-emulator: could not set state blob type %d : %s",
-                     type, strerror(errno));
+        error_setg_errno(errp, errno,
+                         "tpm-emulator: could not set state blob type %d",
+                         type);
         return -1;
     }
 
     /* now the body */
     n = qemu_chr_fe_write_all(&tpm_emu->ctrl_chr, tsb->buffer, tsb->size);
     if (n != tsb->size) {
-        error_report("tpm-emulator: Writing the stateblob (type %d) "
-                     "failed; could not write %u bytes, but only %zd",
-                     type, tsb->size, n);
+        error_setg(errp, "tpm-emulator: Writing the stateblob (type %d) "
+                   "failed; could not write %u bytes, but only %zd",
+                   type, tsb->size, n);
         return -1;
     }
 
@@ -856,17 +858,17 @@ static int tpm_emulator_set_state_blob(TPMEmulator *tpm_emu,
     n = qemu_chr_fe_read_all(&tpm_emu->ctrl_chr,
                              (uint8_t *)&pss, sizeof(pss.u.resp));
     if (n != sizeof(pss.u.resp)) {
-        error_report("tpm-emulator: Reading response from writing stateblob "
-                     "(type %d) failed; expected %zu bytes, got %zd", type,
-                     sizeof(pss.u.resp), n);
+        error_setg(errp, "tpm-emulator: Reading response from writing "
+                   "stateblob (type %d) failed; expected %zu bytes, "
+                   "got %zd", type, sizeof(pss.u.resp), n);
         return -1;
     }
 
     tpm_result = be32_to_cpu(pss.u.resp.tpm_result);
     if (tpm_result != 0) {
-        error_report("tpm-emulator: Setting the stateblob (type %d) failed "
-                     "with a TPM error 0x%x %s", type, tpm_result,
-                     tpm_emulator_strerror(tpm_result));
+        error_setg(errp, "tpm-emulator: Setting the stateblob (type %d) "
+                   "failed with a TPM error 0x%x %s", type, tpm_result,
+                   tpm_emulator_strerror(tpm_result));
         return -1;
     }
 
@@ -880,7 +882,7 @@ static int tpm_emulator_set_state_blob(TPMEmulator *tpm_emu,
  *
  * Returns a negative errno code in case of error.
  */
-static int tpm_emulator_set_state_blobs(TPMBackend *tb)
+static int tpm_emulator_set_state_blobs(TPMBackend *tb, Error **errp)
 {
     TPMEmulator *tpm_emu = TPM_EMULATOR(tb);
     TPMBlobBuffers *state_blobs = &tpm_emu->state_blobs;
@@ -894,13 +896,13 @@ static int tpm_emulator_set_state_blobs(TPMBackend *tb)
 
     if (tpm_emulator_set_state_blob(tpm_emu, PTM_BLOB_TYPE_PERMANENT,
                                     &state_blobs->permanent,
-                                    state_blobs->permanent_flags) < 0 ||
+                                    state_blobs->permanent_flags, errp) < 0 ||
         tpm_emulator_set_state_blob(tpm_emu, PTM_BLOB_TYPE_VOLATILE,
                                     &state_blobs->volatil,
-                                    state_blobs->volatil_flags) < 0 ||
+                                    state_blobs->volatil_flags, errp) < 0 ||
         tpm_emulator_set_state_blob(tpm_emu, PTM_BLOB_TYPE_SAVESTATE,
                                     &state_blobs->savestate,
-                                    state_blobs->savestate_flags) < 0) {
+                                    state_blobs->savestate_flags, errp) < 0) {
         return -EIO;
     }
 
@@ -948,12 +950,12 @@ static void tpm_emulator_vm_state_change(void *opaque, bool running,
  *
  * Returns negative errno codes in case of error.
  */
-static int tpm_emulator_post_load(void *opaque, int version_id)
+static int tpm_emulator_post_load(void *opaque, int version_id, Error **errp)
 {
     TPMBackend *tb = opaque;
     int ret;
 
-    ret = tpm_emulator_set_state_blobs(tb);
+    ret = tpm_emulator_set_state_blobs(tb, errp);
     if (ret < 0) {
         return ret;
     }
@@ -969,7 +971,7 @@ static const VMStateDescription vmstate_tpm_emulator = {
     .name = "tpm-emulator",
     .version_id = 0,
     .pre_save = tpm_emulator_pre_save,
-    .post_load = tpm_emulator_post_load,
+    .post_load_errp = tpm_emulator_post_load,
     .fields = (const VMStateField[]) {
         VMSTATE_UINT32(state_blobs.permanent_flags, TPMEmulator),
         VMSTATE_UINT32(state_blobs.permanent.size, TPMEmulator),

-- 
2.50.1