Add livepatchable command to check if a library is livepatchable

The new command:

$ ulp livepatchable <library>

can be used to check if a certain library is livepatchable.

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

tests/Makefile.am

@@ -490,6 +490,7 @@ TESTS = \
   revert_and_patch.py \
   process.py \
   process_revert.py \
+  livepatchable.py \
   manyprocesses.py
 
 XFAIL_TESTS = \

tests/livepatchable.py

@@ -0,0 +1,27 @@
+#!/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
+
+if testsuite.is_library_livepatchable('.libs/libexception.so') == True:
+  exit(0)
+
+exit(1)

tests/testsuite.py

@@ -40,6 +40,20 @@
 builddir = os.getcwd()
 ulptool = builddir + '/../tools/ulp'
 
+# Check if certain library is livepatchable.
+def is_library_livepatchable(library):
+  command = [ulptool, "livepatchable", library]
+
+  try:
+    tool = subprocess.run(command, timeout=10, stderr=subprocess.STDOUT)
+  except subprocess.TimeoutExpired:
+    print('ulp tool deadlock');
+    return False
+
+  if tool.returncode == 0:
+    return True
+  return False
+
 # Wrapper around pexpect.spawn that automatically sets userspace livepatching
 # requirements, such as LD_PRELOAD'ing libpulp.so, as well as extends its
 # functionality with live patching operations.

tools/Makefile.am

@@ -31,7 +31,8 @@ noinst_HEADERS = \
   dump.h \
   post.h \
   revert.h \
-  messages.h
+  messages.h \
+  livepatchable.h
 
 ulp_SOURCES = \
   ulp.c \
@@ -45,7 +46,8 @@ ulp_SOURCES = \
   revert.c \
   messages.c \
   introspection.c \
-  ptrace.c
+  ptrace.c \
+  livepatchable.c
 ulp_LDADD = $(top_builddir)/common/libcommon.la -lelf -ldl $(LIBUNWIND_LIBS)
 
 # Ensure access to the include directory

tools/arguments.h

@@ -37,6 +37,7 @@ typedef enum
   ULP_POST,
   ULP_REVERSE,
   ULP_MESSAGES,
+  ULP_LIVEPATCHABLE,
 } command_t;
 
 struct arguments

tools/livepatchable.c

@@ -0,0 +1,72 @@
+/*
+ *  libpulp - User-space Livepatching Library
+ *
+ *  Copyright (C) 2017-2021 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 <errno.h>
+#include <fcntl.h>
+#include <libelf.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#include "arguments.h"
+#include "config.h"
+#include "introspection.h"
+#include "livepatchable.h"
+#include "msg_queue.h"
+#include "post.h"
+#include "ulp_common.h"
+
+int
+run_livepatchable(struct arguments *arguments)
+{
+  int ret = 0;
+  int fd;
+
+  /* Set the verbosity level in the common introspection infrastructure. */
+  ulp_verbose = arguments->verbose;
+  ulp_quiet = arguments->quiet;
+
+  fd = open(arguments->args[0], 0);
+  if (fd == -1)
+    errx(EXIT_FAILURE, "Unable to open file '%s': %s.\n", arguments->args[0],
+         strerror(errno));
+
+  elf_version(EV_CURRENT);
+  Elf *elf = elf_begin(fd, ELF_C_READ, NULL);
+
+  struct Elf_Scn *scn =
+      find_section_by_name(elf, "__patchable_function_entries");
+  if (scn == NULL) {
+    WARN("file '%s' is not livepatchable: Missing "
+         "__patchable_function_entries section.",
+         arguments->args[0]);
+    ret = 1;
+  }
+  else {
+    WARN("file '%s' is livepatchable.", arguments->args[0]);
+    ret = 0;
+  }
+
+  elf_end(elf);
+  close(fd);
+
+  return ret;
+}

tools/livepatchable.h

@@ -0,0 +1,29 @@
+/*
+ *  libpulp - User-space Livepatching Library
+ *
+ *  Copyright (C) 2017-2022 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/>.
+ */
+
+#ifndef LIVEPATCHABLE_H
+#define LIVEPATCHABLE_H
+
+struct arguments;
+
+int run_livepatchable(struct arguments *);
+
+#endif /* LIVEPATCHABLE.H */

tools/post.c

@@ -42,8 +42,8 @@ static Elf *elf;
  * such section is found. Exits in error if the string table containing
  * sections names is not found.
  */
-static Elf_Scn *
-find_section_by_name(const char *name)
+Elf_Scn *
+find_section_by_name(Elf *elf, const char *name)
 {
   char *str;
   size_t string_table;
@@ -95,9 +95,9 @@ merge_nops_at_addr(Elf64_Addr addr, size_t amount)
   }
 
   /* Use the .symtab if available, otherwise, the .dynsym. */
-  scn = find_section_by_name(".symtab");
+  scn = find_section_by_name(elf, ".symtab");
   if (scn == NULL)
-    scn = find_section_by_name(".dynsym");
+    scn = find_section_by_name(elf, ".dynsym");
   if (scn == NULL)
     return;
   data = elf_getdata(scn, NULL);
@@ -141,7 +141,7 @@ nops_fixup(void)
   Elf64_Shdr *shdr;
   Elf64_Addr addr;
 
-  scn = find_section_by_name("__patchable_function_entries");
+  scn = find_section_by_name(elf, "__patchable_function_entries");
   if (scn == NULL)
     return;
   data = elf_getdata(scn, NULL);
@@ -183,7 +183,7 @@ run_post(struct arguments *arguments)
   assert(elf_flagelf(elf, ELF_C_SET, ELF_F_LAYOUT));
 
   /* Sanity check. */
-  scn = find_section_by_name("__patchable_function_entries");
+  scn = find_section_by_name(elf, "__patchable_function_entries");
   if (scn == NULL)
     errx(EXIT_FAILURE,
          "Section __patchable_function_entries not found.\n"

tools/post.h

@@ -23,6 +23,10 @@
 #define POST_H
 
 struct arguments;
+struct Elf_Scn;
+struct Elf;
+
+struct Elf_Scn *find_section_by_name(struct Elf *, const char *name);
 
 int run_post(struct arguments *);
 

tools/ulp.c

@@ -32,6 +32,7 @@
 #include "config.h"
 #include "dump.h"
 #include "introspection.h"
+#include "livepatchable.h"
 #include "messages.h"
 #include "packer.h"
 #include "patches.h"
@@ -65,7 +66,8 @@ static const char doc[] =
 "                             with PID\n"
 "   post                      Post process patch container (.so file) in ARG1.\n"
 "   reverse                   Create reverse livepatch from metadata in ARG1.\n"
-"   messages                  Print livepatch information contained in libpulp.\n";
+"   messages                  Print livepatch information contained in libpulp.\n"
+"   livepatchable             Check if .so library in ARG1 is livepatchable.\n";
 
 /* clang-format on */
 
@@ -117,10 +119,15 @@ command_from_string(const char *str)
   };
 
   static const struct entry entries[] = {
-    { "patches", ULP_PATCHES }, { "check", ULP_CHECK },
-    { "dump", ULP_DUMP },       { "packer", ULP_PACKER },
-    { "trigger", ULP_TRIGGER }, { "post", ULP_POST },
-    { "reverse", ULP_REVERSE }, { "messages", ULP_MESSAGES },
+    { "patches", ULP_PATCHES },
+    { "check", ULP_CHECK },
+    { "dump", ULP_DUMP },
+    { "packer", ULP_PACKER },
+    { "trigger", ULP_TRIGGER },
+    { "post", ULP_POST },
+    { "reverse", ULP_REVERSE },
+    { "messages", ULP_MESSAGES },
+    { "livepatchable", ULP_LIVEPATCHABLE },
   };
 
   size_t i;
@@ -206,6 +213,11 @@ handle_end_of_arguments(const struct argp_state *state)
       if (arguments->process_wildcard == 0)
         argp_error(state, "process is mandatory in 'messages' command.");
       break;
+
+    case ULP_LIVEPATCHABLE:
+      if (state->arg_num < 2) {
+        argp_error(state, "file is mandatory in 'livepatchable' command.");
+      }
   }
 }
 
@@ -324,6 +336,10 @@ main(int argc, char **argv)
     case ULP_MESSAGES:
       ret = run_messages(&arguments);
       break;
+
+    case ULP_LIVEPATCHABLE:
+      ret = run_livepatchable(&arguments);
+      break;
   }
 
   return ret;