Add small gdb interface

Livepatch load works but it doesn't modify the addresses because there
is nothing to interpret the insn_queue.

Signed-off-by: Giuliano Belinassi <[email protected]>

include/minielf.h

@@ -63,7 +63,7 @@ long Elf_Load_Section(unsigned dest_size, unsigned char *dest,
 /** ----- ELF functions related to ULP ----- .  */
 
 /** Get the .ulp section from the given ELF file.  */
-int Get_ULP_Section(unsigned dest_size, unsigned char *dest, const char *file);
+long Get_ULP_Section(unsigned dest_size, unsigned char *dest, const char *file);
 
 /** Get the .ulp.rev section from the given ELF file.  */
-int Get_ULP_REV_Section(unsigned dest_size, unsigned char *dest, const char *file);
+long Get_ULP_REV_Section(unsigned dest_size, unsigned char *dest, const char *file);

lib/Makefile.am

@@ -25,7 +25,8 @@ libpulp_la_SOURCES = \
   msg_queue.c \
   insn_queue.c \
   error.c \
-  minielf.c
+  minielf.c \
+  gdb_interface.c
 
 libpulp_la_LDFLAGS = \
   -ldl \

lib/gdb_interface.c

@@ -0,0 +1,131 @@
+/*
+ *  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 interface that allows livepatches to be applied or reverted
+ * within gdb.  */
+
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+
+#include <string.h>
+#include <sys/types.h>
+#include <link.h>
+
+#include "config.h"
+#include "ulp_common.h"
+#include "ulp.h"
+#include "minielf.h"
+#include "error_common.h"
+
+extern char __ulp_metadata_buffer[ULP_METADATA_BUF_LEN];
+
+int
+inject_lp_path(const char *path, long metadata_size)
+{
+  /* FIXME: This is absurdly awkward.  */
+
+  /* Copy the final metadata into final_meta buffer.  Things works here as
+   * follows:
+   *
+   * 1. Copy the first 1 + 32 bytes containing the patch type and patch id.
+   * 2. Copy the size of the path to the livepatch container file.
+   * 3. Copy the path to the livepatch container file.
+   * 4. Copy the remaining metadata stuff.
+   *
+   * We do it in this way so we don't have to carry the path to the patch
+   * container with the patch. This info can be retrieved from the path to
+   * patch and avoid problems regarding the application running in another path
+   * than the ulp tool.
+   *
+   * See introspection.c: 1868.
+   * */
+
+  long metadata_left = 1 + 32;
+  long metadata_right = metadata_size - metadata_left;
+
+
+  char *head = &__ulp_metadata_buffer[metadata_left];
+
+  uint32_t path_size = strlen(path) + 1;
+  uint32_t path_object_size = sizeof(uint32_t) + path_size;
+
+  /* Check if it will still fit the metadata buffer.  */
+  if (metadata_size + path_object_size > ULP_METADATA_BUF_LEN) {
+    /* Won't fit.  */
+    return ENOMEM;
+  }
+
+  /* Shift right so it fits.  */
+  memmove(head + path_object_size, head, metadata_right);
+
+  /* Inject the path.  */
+  memcpy(head, &path_size, sizeof(uint32_t));
+  head += sizeof(uint32_t);
+
+  memcpy(head, path, path_size);
+  head += path_object_size;
+
+  return 0;
+}
+
+int
+gdb_ulp_apply(const char *path)
+{
+  /* Prepare the ULP metadata buffer.  */
+  memset(__ulp_metadata_buffer, '\0', ULP_METADATA_BUF_LEN);
+
+  /* Load the .ulp section into the metadata buffer.  */
+  long len = Get_ULP_Section(ULP_METADATA_BUF_LEN, (void*)__ulp_metadata_buffer, path);
+  if (len < 0) {
+    /* Invalid.  */
+    return (int) -len;
+  }
+
+  if (inject_lp_path(path, len)) {
+    return EINVALIDULP;
+  }
+
+  /* Trigger the livepatch.  */
+  return  __ulp_apply_patch();
+}
+
+
+int
+gdb_ulp_revert(const char *path)
+{
+  /* Prepare the ULP metadata buffer.  */
+  memset(__ulp_metadata_buffer, '\0', ULP_METADATA_BUF_LEN);
+
+  /* Load the .ulp section into the metadata buffer.  */
+  long len = Get_ULP_REV_Section(ULP_METADATA_BUF_LEN, (void *)__ulp_metadata_buffer, path);
+  if (len < 0) {
+    /* Invalid.  */
+    return (int) -len;
+  }
+
+  if (inject_lp_path(path, len)) {
+    return EINVALIDULP;
+  }
+
+  /* Trigger the livepatch.  */
+  return __ulp_apply_patch();
+}

lib/minielf.c

@@ -187,15 +187,15 @@ long Elf_Load_Section(unsigned dest_size, unsigned char *dest,
 }
 
 /** Load the .ulp section of livepatch of `file` into the buffer.  */
-static int
+static long
 Get_Elf_Section(unsigned dest_size, unsigned char *dest,
                 const char *section_name, const char *file)
 {
   /* Open ELF file.  */
   int elf_fd = open(file, O_RDONLY);
   if (elf_fd < 0) {
     warn("Unable to open file %s: %s", file, strerror(errno));
-    return ENOENT;
+    return -ENOENT;
   }
 
   /* Load ELF file header.  */
@@ -205,7 +205,7 @@ Get_Elf_Section(unsigned dest_size, unsigned char *dest,
     warn("File is not an ELF object.");
 
     close(elf_fd);
-    return EINVAL;
+    return -EINVAL;
   }
 
   /* Load ELF section string table.  */
@@ -221,27 +221,27 @@ Get_Elf_Section(unsigned dest_size, unsigned char *dest,
     warn("Section %s not found.", section_name);
 
     close(elf_fd);
-    return EINVAL;
+    return -EINVAL;
   }
 
   /* Load ELF section into dest.  */
-  long x = Elf_Load_Section(dest_size, dest, &ulp_shdr, elf_fd);
-  if (x == 0) {
+  long len = Elf_Load_Section(dest_size, dest, &ulp_shdr, elf_fd);
+  if (len == 0) {
     close(elf_fd);
-    return EINVAL;
+    return -EINVAL;
   }
 
   close(elf_fd);
-  return 0;
+  return len;
 }
 
-int
+long
 Get_ULP_Section(unsigned dest_size, unsigned char *dest, const char *file)
 {
   return Get_Elf_Section(dest_size, dest, ".ulp", file);
 }
 
-int
+long
 Get_ULP_REV_Section(unsigned dest_size, unsigned char *dest, const char *file)
 {
   return Get_Elf_Section(dest_size, dest, ".ulp.rev", file);

tools/introspection.c

@@ -1848,6 +1848,9 @@ extract_ulp_from_so_to_mem(const char *livepatch, bool revert, char **out,
   char *final_meta = (char *)malloc(meta_size);
   char *meta_head = final_meta;
 
+
+  /* FIXME: This is absurdly awkward.  */
+
   /* Copy the final metadata into final_meta buffer.  Things works here as
    * follows:
    *