Introduce GDB interface

common/Makefile.am

@@ -23,4 +23,7 @@ noinst_LTLIBRARIES = libcommon.la
 # Ensure access to the include directory
 AM_CFLAGS += -I$(abs_top_srcdir)/include
 
-libcommon_la_SOURCES = common.c
+# Add -fno-strict-alias to the insn_queue code.
+insn_queue.lo : CFLAGS += -fno-strict-aliasing
+
+libcommon_la_SOURCES = common.c insn_queue.c

common/insn_queue.c

@@ -0,0 +1,128 @@
+/*
+ *  libpulp - User-space Livepatching Library
+ *
+ *  Copyright (C) 2023 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 "ulp_common.h"
+#include "insn_queue.h"
+#include "error_common.h"
+
+#include <assert.h>
+#include <stdio.h>
+
+/** @brief Interpret a print instruction.
+ *
+ * @param insn    Instruction to interpet. Must be a print instruction.
+ *
+ * @return        Size of interpreted instruction.
+ */
+int
+insn_interpret_print(struct ulp_insn *insn)
+{
+  struct ulp_insn_print *p_insn = (struct ulp_insn_print *)insn;
+
+  printf("%s\n", p_insn->bytes);
+  return insn->size;
+}
+
+/** @brief Interpret NOP instruction.
+ *
+ * @param insn    Instruction to interpet. Must be a NOP instruction.
+ *
+ * @return        Size of interpreted instruction (always 1 byte).
+ */
+int
+insn_interpret_nop(struct ulp_insn *insn)
+{
+  return sizeof(*insn);
+}
+
+/* Writes are specific from libpulp and libpulp-tools:
+ *  - On tools, use ptrace.
+ *  - On libpulp, set text permission and use memcpy.
+ */
+int
+insn_interpret_write(struct ulp_insn *insn);
+
+/** Table of decoders.  Index must match the `enum ulp_insn_table` object.  */
+static int (*decoders[ULP_NUM_INSNS])(struct ulp_insn *insn) = {
+  insn_interpret_nop,
+  insn_interpret_print,
+  insn_interpret_write,
+};
+
+/** @brief Interpret the given instruction.
+ *
+ * This function will interpret the given instruction.
+ *
+ * @param insn      Instruction to interpret.
+ *
+ * @return          Size of instruction interpreted.
+ */
+int
+insn_interpret(struct ulp_insn *insn)
+{
+  int index = (int)insn->type;
+  return (decoders[index])(insn);
+}
+
+/** @brief Interpret the instructions in queue.
+ *
+ * Interpret all instructions inserted into the queue object.
+ *
+ * @param queue
+ */
+int
+insnq_interpret(insn_queue_t *queue)
+{
+  int pc = 0; /* Like a CPU program counter.  */
+  int num_insns_executed = 0;
+
+  int size = queue->size;
+  int num_insns = queue->num_insns;
+  char *buffer = queue->buffer;
+
+  while (num_insns_executed < num_insns) {
+    struct ulp_insn *insn = (struct ulp_insn *)&buffer[pc];
+    if (ulp_insn_valid(insn)) {
+      pc += insn_interpret(insn);
+      num_insns_executed++;
+    }
+    else {
+      /* Abort if an invalid insn is received.  */
+      WARN("insnq: invalid insn with opcode %d. Further insns will be "
+           "ignored.", (int)insn->type);
+      return EINSNQ;
+    }
+  }
+
+  /* The pc should stop at the size of the queue.  */
+  if (pc != size) {
+    WARN("insnq: there are bytes left in the instruction queue");
+    return EINSNQ;
+  }
+
+  /* Number of instructions should match what is in the queue.  */
+  if (num_insns_executed != num_insns) {
+    WARN("insnq: not all instructions executed");
+    return EINSNQ;
+  }
+
+  return 0;
+}

configure.ac

@@ -150,6 +150,16 @@ AC_SUBST([LIBUNWIND_LIBS], ["-lunwind-generic -lunwind-ptrace -lunwind"])
 AC_DEFINE(ENABLE_STACK_CHECK, 1, [Enable stack checking routines]),
 AC_DEFINE(ENABLE_STACK_CHECK, 0, [Disable stack checking routines]))
 
+# Enable a gdb interface so that livepatches can be triggered within gdb.
+AC_ARG_ENABLE(gdb-interface,
+AS_HELP_STRING([--enable-gdb-interface],
+[build and exposes an interface for livepatching withing gdb. [default=no]]),
+[enable_gdb_interface=yes],
+[enable_gdb_interface=no; break])
+
+AS_IF([test "$enable_gdb_interface" = "yes"],
+AC_DEFINE(ENABLE_GDB_INTERFACE, 1, [Enable gdb interface for livepatching]))
+
 # Check if libseccomp is present.  This is required for testing.
 CFLAGS="$CFLAGS -I/usr/include/libseccomp/"
 AC_CHECK_HEADER([seccomp.h],,

include/Makefile.am

@@ -27,7 +27,8 @@ noinst_HEADERS = \
 	terminal_colors.h \
 	ld_rtld.h \
 	insn_queue.h \
-	insn_queue_lib.h
+	insn_queue_lib.h \
+	minielf.h
 
 # Workaround a bug in Autoconf 2.69
 if CPU_X86_64

include/insn_queue.h

@@ -138,4 +138,13 @@ ulp_insn_valid(struct ulp_insn *insn)
   }
 }
 
+
+/** @brief Interpret the instructions in queue.
+ *
+ * Interpret all instructions inserted into the queue object.
+ *
+ * @param queue
+ */
+int insnq_interpret(insn_queue_t *queue);
+
 #endif /* INSNQ_H */

include/insn_queue_lib.h

@@ -32,4 +32,12 @@ ulp_error_t insnq_insert_write(void *addr, int n, const void *bytes);
 
 int insnq_ensure_emptiness(void);
 
+/* Not necessary if compiling without gdb interface.  */
+#ifdef ENABLE_GDB_INTERFACE
+
+/** Interpret the global instruction queue from process side.  */
+int insnq_interpret_from_lib(void);
+
+#endif //ENABLE_GDB_INTERFACE
+
 #endif

include/minielf.h

@@ -0,0 +1,74 @@
+/*
+ *  libpulp - User-space Livepatching Library
+ *
+ *  Copyright (C) 2024 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/>.
+ */
+
+/* Small parser for elf, not depending on larger libraries such as libelf
+ * and with very small memory footprint.  No allocation on the heap is done
+ * in this library.
+ */
+
+/* This file is not needed if we are compiling without gdb interface.  */
+#ifdef ENABLE_GDB_INTERFACE
+
+#include <elf.h>
+
+/** Maximum size of the Section String Table.  */
+#define STRTBL_SIZE_MAX       0x500
+
+/** Typedefs so we can adjust according to architecture.  */
+typedef Elf64_Ehdr Elf_Ehdr;
+typedef Elf64_Shdr Elf_Shdr;
+typedef Elf64_Half Elf_Half;
+typedef Elf64_Off  Elf_Off;
+
+/** Read the Elf File Header.  */
+Elf_Ehdr *Elf_Parse_Ehdr(Elf_Ehdr *ehdr, int fd);
+
+/** Get an ELF section by its name.
+  *
+  * OBS: use `readelf -S <file>` to show section names.
+  */
+Elf_Shdr *Elf_Get_Shdr_By_Name(Elf_Shdr *shdr, const char *name, int fd,
+                               const Elf_Ehdr *ehdr, const char strtbl[]);
+
+
+/** Get an ELF section by its index.
+  *
+  * OBS: use `readelf -S <file>` to show section index [<idx>].
+  */
+Elf_Shdr *Elf_Get_Shdr(Elf_Shdr *shdr, Elf_Half index,
+                       int fd, const Elf_Ehdr *ehdr);
+
+/** Get the section string table.  */
+long Elf_Load_Strtbl(char strtbl[STRTBL_SIZE_MAX], const Elf_Ehdr *ehdr, int fd);
+
+/** Load Section into `dest` buffer.  */
+long Elf_Load_Section(unsigned dest_size, unsigned char *dest,
+                      const Elf_Shdr *shdr, int fd);
+
+/** ----- ELF functions related to ULP ----- .  */
+
+/** Get the .ulp section from the given ELF file.  */
+long Get_ULP_Section(unsigned dest_size, unsigned char *dest, const char *file);
+
+/** Get the .ulp.rev section from the given ELF file.  */
+long Get_ULP_REV_Section(unsigned dest_size, unsigned char *dest, const char *file);
+
+#endif //ENABLE_GDB_INTERFACE

include/ulp_common.h

@@ -22,11 +22,13 @@
 #ifndef _ULP_LIB_COMMON_
 #define _ULP_LIB_COMMON_
 
+#include "config.h"
 #include <elf.h>
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <time.h>
+#include <sys/types.h>
 
 #define OUT_PATCH_NAME "metadata.ulp"
 #define OUT_REVERSE_NAME "reverse.ulp"

lib/Makefile.am

@@ -24,7 +24,9 @@ libpulp_la_SOURCES = \
   interpose.c \
   msg_queue.c \
   insn_queue.c \
-  error.c
+  error.c \
+  minielf.c \
+  gdb_interface.c
 
 libpulp_la_LDFLAGS = \
   -ldl \