Find address of reference to symbol by its name

Before this patch, the user could only specify
```
 #target_symbol:target_symbol_ref:addr1:addr2
```
however, those address can change when you modify the livepatch
sourcecode. Therefore, we now support:
```
 #target_symbol:target_symbol_ref
```
and now `addr1` and `addr2` will be collected analysing the target
library and livepatch container automatically on packer time.

Signed-off-by: Giuliano Belinassi <gbelinassi@suse.de>

lib/ulp.c

@@ -833,7 +833,17 @@ ulp_apply_all_units(struct ulp_metadata *ulp)
   /* Now patch static data references in the live patch object */
   ref = ulp->refs;
   while (ref) {
-    uintptr_t patch_address = patch_base + ref->patch_offset;
+    uintptr_t patch_address;
+    if (ref->patch_offset == 0) {
+      /* In case the user did not specify the patch offset, try to find the
+         symbol's address by its name.  */
+      patch_address =
+          (uintptr_t)load_so_symbol(ref->reference_name, ulp->so_handler);
+      ref->patch_offset = patch_address - patch_base;
+    }
+    else {
+      patch_address = patch_base + ref->patch_offset;
+    }
     if (ref->tls) {
       tls_index ti = { .ti_module = tls_idx, .ti_offset = ref->target_offset };
       memcpy((void *)patch_address, &ti, sizeof(ti));

tests/Makefile.am

@@ -190,6 +190,7 @@ check_LTLIBRARIES += libdozens_livepatch1.la \
                      libaddress_livepatch1.la \
                      libcontract_livepatch1.la \
                      libaccess_livepatch1.la \
+                     libaccess_livepatch2.la \
                      libtls_livepatch1.la \
                      libbuildid_livepatch1.la \
                      libmanyprocesses_livepatch1.la
@@ -242,6 +243,9 @@ libcontract_livepatch1_la_LDFLAGS = $(CONVENIENCE_LDFLAGS)
 libaccess_livepatch1_la_SOURCES = libaccess_livepatch1.c
 libaccess_livepatch1_la_LDFLAGS = $(CONVENIENCE_LDFLAGS)
 
+libaccess_livepatch2_la_SOURCES = libaccess_livepatch2.c
+libaccess_livepatch2_la_LDFLAGS = $(CONVENIENCE_LDFLAGS)
+
 libtls_livepatch1_la_SOURCES = libtls_livepatch1.c
 libtls_livepatch1_la_LDFLAGS = $(CONVENIENCE_LDFLAGS)
 
@@ -303,6 +307,9 @@ METADATA = \
   libaccess_livepatch1.dsc \
   libaccess_livepatch1.ulp \
   libaccess_livepatch1.rev \
+  libaccess_livepatch2.dsc \
+  libaccess_livepatch2.ulp \
+  libaccess_livepatch2.rev \
   libtls_livepatch1.dsc \
   libtls_livepatch1.ulp \
   libtls_livepatch1.rev \
@@ -331,6 +338,7 @@ EXTRA_DIST = \
   libaddress_livepatch1.in \
   libcontract_livepatch1.in \
   libaccess_livepatch1.in \
+  libaccess_livepatch2.in \
   libtls_livepatch1.in \
   libbuildid_livepatch1.in \
   libmanyprocesses_livepatch1.in
@@ -482,6 +490,7 @@ TESTS = \
   exception_handling.py \
   missing_function.py \
   access.py \
+  access2.py \
   tls.py \
   buildid.py \
   libpulp_messages.py \

tests/access2.c

@@ -0,0 +1,58 @@
+/*
+ *  libpulp - User-space Livepatching Library
+ *
+ *  Copyright (C) 2021 SUSE Software Solutions GmbH
+ *
+ *  This file is part of libpulp.
+ *
+ *  libpulp is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  libpulp is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with libpulp.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <errno.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <libaccess.h>
+
+int
+main(void)
+{
+  char buffer[128];
+
+  /* Original banner. */
+  printf("Banner addr: 0x%lX\n", (unsigned long)banner_get());
+  printf("%s\n", banner_get());
+
+  /* Use original banner setting function. */
+  banner_set(strdup("Banner changed from main"));
+  printf("%s\n", banner_get());
+
+  /* Wait for input. */
+  if (fgets(buffer, sizeof(buffer), stdin) == NULL) {
+    if (errno) {
+      perror("access");
+      return 1;
+    }
+  }
+
+  /*
+   * Use banner setting function again, which is supposed to have been
+   * changed by the test driver. The patched function ignores the
+   * argument, so 'String from main' should not be in the output.
+   */
+  banner_set("String from main");
+  printf("%s\n", banner_get());
+
+  return 0;
+}

tests/access2.py

@@ -0,0 +1,37 @@
+#!/usr/bin/env python3
+
+#   libpulp - User-space Livepatching Library
+#
+#   Copyright (C) 2021 SUSE Software Solutions GmbH
+#
+#   This file is part of libpulp.
+#
+#   libpulp is free software; you can redistribute it and/or
+#   modify it under the terms of the GNU Lesser General Public
+#   License as published by the Free Software Foundation; either
+#   version 2.1 of the License, or (at your option) any later version.
+#
+#   libpulp is distributed in the hope that it will be useful,
+#   but WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+#   Lesser General Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License
+#   along with libpulp.  If not, see <http://www.gnu.org/licenses/>.
+
+import testsuite
+
+child = testsuite.spawn('access')
+
+child.expect('Original banner')
+child.expect('Banner changed from main')
+
+child.livepatch('libaccess_livepatch2.ulp')
+
+child.sendline('')
+child.expect('String from live patch',
+             reject=['String from main',
+                     'Live patch data references not initialized'])
+
+child.close(force=True)
+exit(0)

tests/libaccess_livepatch2.c

@@ -0,0 +1,47 @@
+/*
+ *  libpulp - User-space Livepatching Library
+ *
+ *  Copyright (C) 2021 SUSE Software Solutions GmbH
+ *
+ *  This file is part of libpulp.
+ *
+ *  libpulp is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  libpulp is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with libpulp.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <err.h>
+#include <stdlib.h>
+
+#include <libaccess.h>
+
+char **ulpr_banner = NULL;
+static char *ulpr_string = "String from live patch";
+
+void
+new_banner_set(__attribute__((unused)) char *new)
+{
+  if (ulpr_banner == NULL)
+    errx(EXIT_FAILURE, "Live patch data references not initialized");
+
+  *ulpr_banner = ulpr_string;
+}
+
+/*
+ * Touch ulpr_banner so that it does not get optimized away or placed into
+ * read-only sections.
+ */
+void
+banner_disturb(void)
+{
+  ulpr_banner++;
+}

tests/libaccess_livepatch2.in

@@ -0,0 +1,4 @@
+__ABS_BUILDDIR__/.libs/libaccess_livepatch2.so
+@__ABS_BUILDDIR__/.libs/libaccess.so.0
+banner_set:new_banner_set
+#banner:ulpr_banner

tests/offsets.py

@@ -68,8 +68,10 @@ def find_offset(file, name):
     poff = find_offset(patch, pname)
 
     # Replace offset template patterns with actual offsets
-    line = line.replace('__TARGET_OFFSET__', toff)
-    line = line.replace('__PATCH_OFFSET__', poff)
+    if toff is not None:
+        line = line.replace('__TARGET_OFFSET__', toff)
+    if poff is not None:
+        line = line.replace('__PATCH_OFFSET__', poff)
 
   # Write every line back to the output file
   ofile.write(line)

tools/introspection.c

@@ -1687,7 +1687,8 @@ check_livepatch_functions_matches_metadata(void)
     symbol = dlsym(container_handle, new_fname);
 
     if (!symbol) {
-      WARN("symbol %s is not present in the livepatch container.", new_fname);
+      WARN("symbol %s is not present in the livepatch container: %s",
+           new_fname, dlerror());
       ret = EINVAL;
       break;
     }

tools/packer.c

@@ -35,6 +35,9 @@
 #include "packer.h"
 #include "ulp_common.h"
 
+static int get_elf_tgt_ref_addrs(Elf *, struct ulp_reference *, Elf_Scn *,
+                                 Elf_Scn *);
+
 void
 free_metadata(struct ulp_metadata *ulp)
 {
@@ -170,12 +173,14 @@ get_build_id_note(Elf *elf)
 }
 
 int
-get_ulp_elf_metadata(const char *filename, struct ulp_object *obj)
+get_ulp_elf_metadata(const char *filename, struct ulp_metadata *ulp)
 {
   int fd, ret;
   Elf *elf;
   Elf_Scn *dynsym;
   Elf_Scn *symtab = NULL;
+  struct ulp_object *obj = ulp->objs;
+  struct ulp_reference *ref = ulp->refs;
 
   fd = 0;
   elf = load_elf(filename, &fd);
@@ -206,6 +211,12 @@ get_ulp_elf_metadata(const char *filename, struct ulp_object *obj)
     goto clean_elf;
   }
 
+  if (!get_elf_tgt_ref_addrs(elf, ref, dynsym, symtab)) {
+    WARN("Unable to get target reference addresses.");
+    ret = 0;
+    goto clean_elf;
+  }
+
   ret = 1;
 
 clean_elf:
@@ -225,6 +236,18 @@ get_object_metadata(Elf *elf, struct ulp_object *obj)
   return 1;
 }
 
+/** @brief Get offsets of symbols in target library
+ *
+ * This function gather the address of all to-be-patched functions in the
+ * target library.
+ *
+ * @param elf     The target library elf object.
+ * @param obj     Chain of objects.
+ * @param st1     Symbol table 1, usually .dymsym.
+ * @param st2     Symbol table 2, usually .symtab if present.
+ *
+ * @return 1
+ */
 int
 get_elf_tgt_addrs(Elf *elf, struct ulp_object *obj, Elf_Scn *st1, Elf_Scn *st2)
 {
@@ -242,6 +265,40 @@ get_elf_tgt_addrs(Elf *elf, struct ulp_object *obj, Elf_Scn *st1, Elf_Scn *st2)
   return 1;
 }
 
+/** @brief Get offsets of references to symbol in target library
+ *
+ * When the user doesn't specify the offset of the target symbol in the target
+ * library when using the # syntax, try to find it by looking into the target
+ * library symbols.
+ *
+ * @param elf     The target library elf object.
+ * @param ref     Chain of references.
+ * @param st1     Symbol table 1, usually .dymsym.
+ * @param st2     Symbol table 2, usually .symtab if present.
+ *
+ * @return 1
+ */
+static int
+get_elf_tgt_ref_addrs(Elf *elf, struct ulp_reference *ref, Elf_Scn *st1,
+                      Elf_Scn *st2)
+{
+
+  while (ref != NULL) {
+    if (ref->target_offset == 0) {
+      ref->target_offset =
+          (uintptr_t)get_symbol_addr(elf, st1, ref->target_name);
+      if (ref->target_offset == 0 && st2 != NULL) {
+        /* In case we couldn't find the symbol there, look in the symtab, if
+         * available.  */
+        ref->target_offset =
+            (uintptr_t)get_symbol_addr(elf, st2, ref->target_name);
+      }
+    }
+    ref = ref->next;
+  }
+  return 1;
+}
+
 int
 create_patch_metadata_file(struct ulp_metadata *ulp, const char *filename)
 {
@@ -496,16 +553,23 @@ parse_description(const char *filename, struct ulp_metadata *ulp)
 
         third = second + 1;
         second = strchr(third, ':');
-        *second = '\0';
-        ref->reference_name = strdup(third);
 
-        third = second + 1;
-        second = strchr(third, ':');
-        *second = '\0';
-        ref->target_offset = (intptr_t)strtol(third, NULL, 16);
+        /* Check if the user manually specified the offsets.  */
+        if (second == NULL)
+          ref->reference_name = strdup(third);
+        else {
+          *second = '\0';
+          ref->reference_name = strdup(third);
 
-        third = second + 1;
-        ref->patch_offset = (intptr_t)strtol(third, NULL, 16);
+          third = second + 1;
+
+          second = strchr(third, ':');
+          *second = '\0';
+          ref->target_offset = (intptr_t)strtol(third, NULL, 16);
+
+          third = second + 1;
+          ref->patch_offset = (intptr_t)strtol(third, NULL, 16);
+        }
 
         ref->next = ulp->refs;
         ulp->refs = ref;
@@ -794,7 +858,7 @@ run_packer(struct arguments *arguments)
   }
   DEBUG("target library: %s.", arguments->library);
 
-  if (!get_ulp_elf_metadata(arguments->library, ulp.objs)) {
+  if (!get_ulp_elf_metadata(arguments->library, &ulp)) {
     WARN("unable to parse target library.");
     goto main_error;
   }

tools/packer.h

@@ -40,7 +40,7 @@ Elf_Scn *get_dynsym(Elf *elf);
 
 Elf_Scn *get_build_id_note(Elf *elf);
 
-int get_ulp_elf_metadata(const char *filename, struct ulp_object *obj);
+int get_ulp_elf_metadata(const char *filename, struct ulp_metadata *ulp);
 
 int get_object_metadata(Elf *elf, struct ulp_object *obj);