analyze: add "srk" verb to extract current srk from TPM2 chip

This is pretty low-level functionality, hence placed in systemd-analyze.
This is useful for working with systemd-cryptenroll --tpm2-device-key=,
as it acquires the SRK without requiring the full tpm2-tss tool set.

man/systemd-analyze.xml

@@ -174,6 +174,11 @@
       <arg choice="plain">pcrs</arg>
       <arg choice="opt" rep="repeat"><replaceable>PCR</replaceable></arg>
     </cmdsynopsis>
+    <cmdsynopsis>
+      <command>systemd-analyze</command>
+      <arg choice="opt" rep="repeat">OPTIONS</arg>
+      <arg choice="plain">srk</arg> &gt;<arg choice="plain"><replaceable>FILE</replaceable></arg>
+    </cmdsynopsis>
   </refsynopsisdiv>
 
   <refsect1>
@@ -926,6 +931,16 @@ NR NAME                SHA256
 23 application-support 0000000000000000000000000000000000000000000000000000000000000000</programlisting>
       </example>
     </refsect2>
+
+    <refsect2>
+      <title><command>systemd-analyze srk &gt; <replaceable>FILE</replaceable></command></title>
+
+      <para>This command reads the Storage Root Key (SRK) from the TPM2 device, and writes it in marshalled
+      TPM2B_PUBLIC format to stdout. Example:</para>
+
+      <programlisting>systemd-analyze srk &gt; srk.tpm2b_public</programlisting>
+    </refsect2>
+
   </refsect1>
 
   <refsect1>

src/analyze/analyze-srk.c

@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include "analyze.h"
+#include "analyze-srk.h"
+#include "tpm2-util.h"
+
+int verb_srk(int argc, char *argv[], void *userdata) {
+#if HAVE_TPM2
+        _cleanup_(tpm2_context_unrefp) Tpm2Context *c = NULL;
+        _cleanup_(Esys_Freep) TPM2B_PUBLIC *public = NULL;
+        int r;
+
+        r = tpm2_context_new(/* device= */ NULL, &c);
+        if (r < 0)
+                return log_error_errno(r, "Failed to create TPM2 context: %m");
+
+        r = tpm2_get_srk(
+                        c,
+                        /* session= */ NULL,
+                        &public,
+                        /* ret_name= */ NULL,
+                        /* ret_qname= */ NULL,
+                        /* ret_handle= */ NULL);
+        if (r < 0)
+                return log_error_errno(r, "Failed to get SRK: %m");
+        if (r == 0)
+                return log_error_errno(SYNTHETIC_ERRNO(ENOENT), "No SRK stored so far.");
+
+        _cleanup_free_ void *marshalled = NULL;
+        size_t marshalled_size = 0;
+        r = tpm2_marshal_public(public, &marshalled, &marshalled_size);
+        if (r < 0)
+                return log_error_errno(r, "Failed to marshal SRK: %m");
+
+        if (isatty(STDOUT_FILENO))
+                return log_error_errno(SYNTHETIC_ERRNO(EIO), "Refusing to write binary data to TTY, please redirect output to file.");
+
+        if (fwrite(marshalled, 1, marshalled_size, stdout) != marshalled_size)
+                return log_error_errno(errno, "Failed to write SRK to stdout: %m");
+
+        fflush(stdout);
+
+        return EXIT_SUCCESS;
+#else
+        return log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "TPM2 support not available.");
+#endif
+}

src/analyze/analyze-srk.h

@@ -0,0 +1,4 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+int verb_srk(int argc, char *argv[], void *userdata);

src/analyze/analyze.c

@@ -32,6 +32,7 @@
 #include "analyze-plot.h"
 #include "analyze-security.h"
 #include "analyze-service-watchdogs.h"
+#include "analyze-srk.h"
 #include "analyze-syscall-filter.h"
 #include "analyze-time.h"
 #include "analyze-time-data.h"
@@ -236,6 +237,7 @@ static int help(int argc, char *argv[], void *userdata) {
                "  malloc [D-BUS SERVICE...]  Dump malloc stats of a D-Bus service\n"
                "  fdstore SERVICE...         Show file descriptor store contents of service\n"
                "  pcrs [PCR...]              Show TPM2 PCRs and their names\n"
+               "  srk > FILE                 Write TPM2 SRK to stdout\n"
                "\nOptions:\n"
                "     --recursive-errors=MODE Control which units are verified\n"
                "     --offline=BOOL          Perform a security review on unit file(s)\n"
@@ -646,6 +648,7 @@ static int run(int argc, char *argv[]) {
                 { "fdstore",           2,        VERB_ANY, 0,            verb_fdstore           },
                 { "image-policy",      2,        2,        0,            verb_image_policy      },
                 { "pcrs",              VERB_ANY, VERB_ANY, 0,            verb_pcrs              },
+                { "srk",               VERB_ANY, 1,        0,            verb_srk               },
                 {}
         };
 

src/analyze/meson.build

@@ -21,6 +21,7 @@ systemd_analyze_sources = files(
         'analyze-plot.c',
         'analyze-security.c',
         'analyze-service-watchdogs.c',
+        'analyze-srk.c',
         'analyze-syscall-filter.c',
         'analyze-time.c',
         'analyze-time-data.c',