[XEN PATCH] tools/xenstore: Log xenstored build ID on startup

* [XEN PATCH] tools/xenstore: Log xenstored build ID on startup
@ 2020-11-13 14:18 Bjoern Doebel
  2020-11-13 14:27 ` Jan Beulich
                   ` (2 more replies)
  0 siblings, 3 replies; 12+ messages in thread
From: Bjoern Doebel @ 2020-11-13 14:18 UTC (permalink / raw)
  To: xen-devel
  Cc: Julien Grall, Eslam Elnikety, Bjoern Doebel, Ian Jackson, Wei Liu

Right now we do not have a mechanism to determine the version of the
currently running xenstored at runtime. As xenstored runs throughout the
lifetime of a Xen host, this may lead to problems when newer user space
builds are staged. Then, the running xenstored will no longer match the
version of the installed xenstored.

To allow users to always identify the running version of xenstored, add
a linker-generated unique build ID to every xenstored build. Add
functionality to log this build ID into a file upon service startup.

Signed-off-by: Bjoern Doebel <doebel@amazon.de>
Reviewed-by: Martin Mazein <amazein@amazon.de>
Reviewed-by: Paul Durrant <pdurrant@amazon.co.uk>
---
 tools/hotplug/Linux/launch-xenstore.in |  2 +-
 tools/xenstore/Makefile                |  4 +++
 tools/xenstore/buildid_symbols.ld      | 10 +++++++
 tools/xenstore/xenstored_core.c        |  8 ++++++
 tools/xenstore/xenstored_core.h        |  3 ++
 tools/xenstore/xenstored_minios.c      |  4 +++
 tools/xenstore/xenstored_posix.c       | 52 ++++++++++++++++++++++++++++++++++
 7 files changed, 82 insertions(+), 1 deletion(-)
 create mode 100644 tools/xenstore/buildid_symbols.ld

diff --git a/tools/hotplug/Linux/launch-xenstore.in b/tools/hotplug/Linux/launch-xenstore.in
index 991dec8d25..a6f2254030 100644
--- a/tools/hotplug/Linux/launch-xenstore.in
+++ b/tools/hotplug/Linux/launch-xenstore.in
@@ -62,7 +62,7 @@ test -f @CONFIG_DIR@/@CONFIG_LEAF_DIR@/xencommons && . @CONFIG_DIR@/@CONFIG_LEAF
 	}
 
 	echo -n Starting $XENSTORED...
-	$XENSTORED --pid-file @XEN_RUN_DIR@/xenstored.pid $XENSTORED_ARGS
+	$XENSTORED --pid-file @XEN_RUN_DIR@/xenstored.pid --buildid-file @XEN_RUN_DIR@/xenstored.buildid $XENSTORED_ARGS
 
 	systemd-notify --booted 2>/dev/null || timeout_xenstore $XENSTORED || exit 1
 
diff --git a/tools/xenstore/Makefile b/tools/xenstore/Makefile
index 9a0f0d012d..c63350980b 100644
--- a/tools/xenstore/Makefile
+++ b/tools/xenstore/Makefile
@@ -66,6 +66,10 @@ $(XENSTORED_OBJS): CFLAGS += $(SYSTEMD_CFLAGS)
 xenstored: LDFLAGS += $(SYSTEMD_LIBS)
 endif
 
+# xenstored: enforce creation of a buildID section and use a linker
+# script to add additional symbols around that section
+xenstored: LDFLAGS +=  -Wl,--build-id=sha1 -Wl,-T,buildid_symbols.ld
+
 $(XENSTORED_OBJS): CFLAGS += $(CFLAGS_libxengnttab)
 
 xenstored: $(XENSTORED_OBJS)
diff --git a/tools/xenstore/buildid_symbols.ld b/tools/xenstore/buildid_symbols.ld
new file mode 100644
index 0000000000..d74024c4e9
--- /dev/null
+++ b/tools/xenstore/buildid_symbols.ld
@@ -0,0 +1,10 @@
+SECTIONS
+{
+       __buildid_note_section = . ;
+       .note.gnu.build-id :
+       {
+               *(.note.gnu.build-id)
+       }
+       __buildid_end = . ;
+}
+INSERT AFTER .data
diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
index b4be374d3f..c6f107bdd9 100644
--- a/tools/xenstore/xenstored_core.c
+++ b/tools/xenstore/xenstored_core.c
@@ -1844,6 +1844,7 @@ static void usage(void)
 
 
 static struct option options[] = {
+	{ "buildid-file", 1, NULL, 'B' },
 	{ "no-domain-init", 0, NULL, 'D' },
 	{ "entry-nb", 1, NULL, 'E' },
 	{ "pid-file", 1, NULL, 'F' },
@@ -1875,12 +1876,16 @@ int main(int argc, char *argv[])
 	bool outputpid = false;
 	bool no_domain_init = false;
 	const char *pidfile = NULL;
+	const char *buildid_file = NULL;
 	int timeout;
 
 
 	while ((opt = getopt_long(argc, argv, "DE:F:HNPS:t:T:RVW:", options,
 				  NULL)) != -1) {
 		switch (opt) {
+		case 'B':
+			buildid_file = optarg;
+			break;
 		case 'D':
 			no_domain_init = true;
 			break;
@@ -1948,6 +1953,9 @@ int main(int argc, char *argv[])
 	if (pidfile)
 		write_pidfile(pidfile);
 
+	if (buildid_file)
+		write_buildid_file(buildid_file);
+
 	/* Talloc leak reports go to stderr, which is closed if we fork. */
 	if (!dofork)
 		talloc_enable_leak_report_full();
diff --git a/tools/xenstore/xenstored_core.h b/tools/xenstore/xenstored_core.h
index 1df6ad94ab..712280626c 100644
--- a/tools/xenstore/xenstored_core.h
+++ b/tools/xenstore/xenstored_core.h
@@ -193,6 +193,9 @@ void xenbus_notify_running(void);
 /* Write out the pidfile */
 void write_pidfile(const char *pidfile);
 
+/* Write the buildid file */
+void write_buildid_file(const char *buildidfile);
+
 /* Fork but do not close terminal FDs */
 void daemonize(void);
 /* Close stdin/stdout/stderr to complete daemonize */
diff --git a/tools/xenstore/xenstored_minios.c b/tools/xenstore/xenstored_minios.c
index c94493e52a..ef1151aee4 100644
--- a/tools/xenstore/xenstored_minios.c
+++ b/tools/xenstore/xenstored_minios.c
@@ -24,6 +24,10 @@ void write_pidfile(const char *pidfile)
 {
 }
 
+void write_buildid_file(const char *buildid_file)
+{
+}
+
 void daemonize(void)
 {
 }
diff --git a/tools/xenstore/xenstored_posix.c b/tools/xenstore/xenstored_posix.c
index 1f9603fea2..ec017611d6 100644
--- a/tools/xenstore/xenstored_posix.c
+++ b/tools/xenstore/xenstored_posix.c
@@ -20,6 +20,7 @@
 #include <sys/stat.h>
 #include <unistd.h>
 #include <fcntl.h>
+#include <stdint.h>
 #include <stdlib.h>
 #include <sys/mman.h>
 
@@ -48,6 +49,57 @@ void write_pidfile(const char *pidfile)
 	close(fd);
 }
 
+/*
+ * We don't have a working elf.h available here, so let's define our very own
+ * data structs and accessor macros for ELF notes.
+ *
+ * https://docs.oracle.com/cd/E23824_01/html/819-0690/chapter6-18048.html:
+ * For 64–bit objects and 32–bit objects, each entry is an array of 4-byte
+ * words in the format of the target processor.
+ */
+typedef struct
+{
+	uint32_t namesz;
+	uint32_t descsz;
+	uint32_t type;
+} elf_note_hdr;
+
+/* ELF Note accessors, copied from Xen's elf.h */
+#define ELFNOTE_ALIGN(_n_) (((_n_)+3)&~3)
+#define ELFNOTE_NAME(_n_) ((char*)(_n_) + sizeof(*(_n_)))
+#define ELFNOTE_DESC(_n_) (ELFNOTE_NAME(_n_) + ELFNOTE_ALIGN((_n_)->namesz))
+/* GNU LD: type == note (NT_GNU_BUILD_ID as in
+ * https://sourceware.org/ml/binutils/2007-07/msg00012.html)*/
+#define NT_GNU_BUILD_ID 3
+
+
+void write_buildid_file(const char *buildid_file)
+{
+	unsigned int i = 0;
+	FILE *fdesc;
+	extern elf_note_hdr __buildid_note_section;
+	unsigned int id_length = __buildid_note_section.descsz;
+	char* desc = ELFNOTE_DESC(&__buildid_note_section);
+
+	if (__buildid_note_section.type != NT_GNU_BUILD_ID)
+		barf("Expected GNU_BUILDID note, but found type '%d'",
+		     __buildid_note_section.type);
+
+	fdesc = fopen(buildid_file, "w+");
+	if (!fdesc)
+		barf_perror("Error opening buildid file %s", buildid_file);
+
+	/* We exit silently if daemon already running. */
+	if (lockf(fileno(fdesc), F_TLOCK, 0) == -1)
+		exit(0);
+
+	for (i = 0; i < id_length; ++i)
+		fprintf(fdesc, "%02x", (unsigned char)desc[i]);
+	fprintf(fdesc, "\n");
+
+	fclose(fdesc);
+}
+
 /* Stevens. */
 void daemonize(void)
 {
-- 
2.16.6




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