units: add a tpm2.target synchronization point and small generator that pulls in

Distributions apparently only compile a subset of TPM2 drivers into the
kernel. For those not compiled it but provided as kmod we need a
synchronization point: we must wait before the first TPM2 interaction
until the driver is available and accessible.

This adds a tpm2.target unit as such a synchronization point. It's
ordered after /dev/tpmrm0, and is pulled in by a generator whenever we
detect that the kernel reported a TPM2 to exist but we have no device
for it yet.

This should solve the issue, but might create problems: if there are TPM
devices supported by firmware that we don't have Linux drivers for we'll
hang for a bit. Hence let's add a kernel cmdline switch to disable (or
alternatively force) this logic.

Fixes: #30164

1 files changed, 6 insertions, 0 deletions

diff --git a/src/tpm2-setup/meson.build b/src/tpm2-setup/meson.build
index c85721c98e..77fad97b7f 100644
--- a/src/tpm2-setup/meson.build
+++ b/src/tpm2-setup/meson.build
@@ -13,4 +13,10 @@ executables += [
                         libopenssl,
                 ],
         },
+
+        generator_template + {
+                'name' : 'systemd-tpm2-generator',
+                'sources' : files('tpm2-generator.c'),
+        },
+
 ]