Object file injection, first part

1 files changed, 233 insertions, 0 deletions

diff --git a/src/model/reladd.c b/src/model/reladd.c
new file mode 100644
index 0000000..782d245
--- /dev/null
+++ b/src/model/reladd.c
@@ -0,0 +1,233 @@
+#include <assert.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <libelf/gelf.h>
+#include <libelfu/libelfu.h>
+
+typedef enum Destsegment {
+  DS_UNKNOWN,
+  DS_TEXT,
+  DS_DATA,
+} Destsegment;
+
+
+static Destsegment destsegment(ElfuScn *ms)
+{
+  if (!(ms->shdr.sh_flags & SHF_ALLOC)) {
+    return DS_UNKNOWN;
+  }
+
+  if (!(ms->shdr.sh_flags & SHF_WRITE)
+      && (ms->shdr.sh_flags & SHF_EXECINSTR)) {
+    return DS_TEXT;
+  } else if ((ms->shdr.sh_flags & SHF_WRITE)
+             && !(ms->shdr.sh_flags & SHF_EXECINSTR)) {
+    return DS_DATA;
+  }
+
+  return DS_UNKNOWN;
+}
+
+
+
+static ElfuScn* insertSection(ElfuElf *me, ElfuElf *mrel, ElfuScn *ms)
+{
+  ElfuPhdr *mp;
+  ElfuPhdr *first = NULL;
+  ElfuPhdr *last = NULL;
+  ElfuScn *newscn = NULL;
+  ElfuPhdr *injAnchor;
+  int searchForCode = 0;
+
+  switch (destsegment(ms)) {
+    case DS_TEXT:
+      searchForCode = 1;
+    case DS_DATA:
+      newscn = elfu_mCloneScn(ms);
+      if (!newscn) {
+        return NULL;
+      }
+
+      /* Find first and last LOAD PHDRs. */
+      CIRCLEQ_FOREACH(mp, &me->phdrList, elem) {
+        if (mp->phdr.p_type != PT_LOAD) {
+          continue;
+        }
+
+        if (!first || mp->phdr.p_vaddr < first->phdr.p_vaddr) {
+          first = mp;
+        }
+        if (!last || mp->phdr.p_vaddr > last->phdr.p_vaddr) {
+          /* No need to check p_memsz as segments may not overlap in memory. */
+          last = mp;
+        }
+      }
+
+      if (searchForCode) {
+        if ((first->phdr.p_flags & PF_X) && !(first->phdr.p_flags & PF_W)) {
+          injAnchor = first;
+        } else if ((last->phdr.p_flags & PF_X) && !(last->phdr.p_flags & PF_W)) {
+          injAnchor = last;
+        } else {
+          injAnchor = NULL;
+        }
+      } else {
+        if ((first->phdr.p_flags & PF_W) && !(first->phdr.p_flags & PF_X)) {
+          injAnchor = first;
+        } else if ((last->phdr.p_flags & PF_W) && !(last->phdr.p_flags & PF_X)) {
+          injAnchor = last;
+        } else {
+          injAnchor = NULL;
+        }
+      }
+
+      if (!injAnchor) {
+        ELFU_WARN("insertSection: Could not find injection anchor.\n"
+                  "               It has to be the first or last segment in the memory image.\n");
+      } else {
+        GElf_Off injOffset;
+
+        /* If the anchor is first or last, insert before or after */
+        if (injAnchor == first) {
+          /* Find first section and inject before it */
+          ElfuScn *firstScn = elfu_mScnFirstInSegment(me, injAnchor);
+          if (!firstScn) {
+            ELFU_WARN("insertSection: mScnFirstInSegment failed.\n");
+
+            // TODO: Error handling
+          } else {
+            injOffset = firstScn->shdr.sh_offset;
+
+            /* Make space */
+            elfu_mInsertSpaceBefore(me, injOffset, ms->shdr.sh_size);
+
+            /* Update memory offset */
+            newscn->shdr.sh_addr = injAnchor->phdr.p_vaddr;
+
+            /* Insert into chain of sections */
+            elfu_mInsertScnInChainBefore(me, firstScn, newscn);
+          }
+        } else {
+          /* Find last section and inject after it */
+          ElfuScn *lastScn = elfu_mScnLastInSegment(me, injAnchor);
+          if (!lastScn) {
+            ELFU_WARN("insertSection: mScnLastInSegment failed.\n");
+
+            // TODO: Error handling
+          } else {
+            injOffset = lastScn->shdr.sh_offset + elfu_gScnSizeFile(&lastScn->shdr);
+
+            /* Expand NOBITS sections at injection site, if any. */
+            elfu_mExpandNobits(me, injOffset);
+
+            /* Recalculate injOffset in case we expanded a NOBITS section */
+            lastScn = elfu_mScnLastInSegment(me, injAnchor);
+            injOffset = lastScn->shdr.sh_offset + elfu_gScnSizeFile(&lastScn->shdr);
+
+            /* Make space */
+            elfu_mInsertSpaceAfter(me, injOffset, ms->shdr.sh_size);
+
+            /* Update memory offset */
+            newscn->shdr.sh_addr = injAnchor->phdr.p_vaddr + (injOffset - injAnchor->phdr.p_offset);
+
+            /* Insert into chain of sections */
+            elfu_mInsertScnInChainAfter(me, lastScn, newscn);
+          }
+        }
+
+        /* Update file offset in new section BEFORE we do anything else */
+        newscn->shdr.sh_offset = injOffset;
+
+        /* Inject name */
+        // TODO
+        newscn->shdr.sh_name = 0;
+
+        // TODO: Relocate
+
+        return newscn;
+      }
+      break;
+
+    case DS_UNKNOWN:
+      ELFU_WARN("insertSection: Don't know where to insert ' %s with flags %jd (type %d).\n",
+                elfu_mScnName(mrel, ms),
+                ms->shdr.sh_flags,
+                ms->shdr.sh_type);
+    default:
+      ELFU_WARN("insertSection: Skipping section %s with flags %jd (type %d).\n",
+                elfu_mScnName(mrel, ms),
+                ms->shdr.sh_flags,
+                ms->shdr.sh_type);
+      return NULL;
+  }
+
+  if (newscn) {
+    // TODO: Destroy newscn
+  }
+  return NULL;
+}
+
+
+
+void elfu_mReladd(ElfuElf *me, ElfuElf *mrel)
+{
+  ElfuScn *ms;
+
+  assert(me);
+  assert(mrel);
+
+
+  /* For each section in object file, guess how to insert it */
+  CIRCLEQ_FOREACH(ms, &mrel->scnList, elem) {
+    ElfuScn *newscn;
+
+    switch(ms->shdr.sh_type) {
+      case SHT_NULL: /* 0 */
+        continue;
+
+      case SHT_PROGBITS: /* 1 */
+        /* Find a place where it belongs and shove it in. */
+        newscn = insertSection(me, mrel, ms);
+        if (!newscn) {
+          ELFU_WARN("mReladd: Could not insert section %s (type %d), skipping.\n",
+                    elfu_mScnName(mrel, ms),
+                    ms->shdr.sh_type);
+        }
+        break;
+
+      case SHT_SYMTAB: /* 2 */
+      case SHT_DYNSYM: /* 11 */
+        /* Merge with the existing table. Take care of string tables also. */
+
+      case SHT_STRTAB: /* 3 */
+        /* May have to be merged with the existing string table for
+         * the symbol table. */
+
+      case SHT_RELA: /* 4 */
+      case SHT_REL: /* 9 */
+        /* Possibly append this in memory to the section model
+         * that it describes. */
+
+      case SHT_NOBITS: /* 8 */
+        /* Expand this to SHT_PROGBITS, then insert as such. */
+
+      case SHT_HASH: /* 5 */
+      case SHT_DYNAMIC: /* 6 */
+      case SHT_SHLIB: /* 10 */
+      case SHT_SYMTAB_SHNDX: /* 18 */
+
+      /* Don't care about the next ones yet. I've never seen
+       * them and they can be implemented when necessary. */
+      case SHT_NOTE: /* 7 */
+      case SHT_INIT_ARRAY: /* 14 */
+      case SHT_FINI_ARRAY: /* 15 */
+      case SHT_PREINIT_ARRAY: /* 16 */
+      case SHT_GROUP: /* 17 */
+      case SHT_NUM: /* 19 */
+      default:
+        ELFU_WARN("mReladd: Skipping section %s (type %d).\n",
+                  elfu_mScnName(mrel, ms),
+                  ms->shdr.sh_type);
+    }
+  }
+}