Implement mInsertBefore, for pre-.interp injection

diff --git a/include/libelfu/modelops.h b/include/libelfu/modelops.h
index 9475eba2a650d473d302ebb1d7b91eff34438c68..c89630f3aed9b07a98ea6e849728a0de8b130474 100644 (file)
--- a/include/libelfu/modelops.h
+++ b/include/libelfu/modelops.h
@@ -17,4 +17,7 @@ int elfu_mCheck(ElfuElf *me);
 ElfuElf* elfu_mFromElf(Elf *e);
     void elfu_mToElf(ElfuElf *me, Elf *e);
 
+
+GElf_Xword elfu_mInsertBefore(ElfuElf *me, GElf_Off off, GElf_Xword size);
+
 #endif

diff --git a/include/options.h b/include/options.h
index f39f01e8de9858f0914af2e78ea325aa7ae65bdd..ee9d612780c026d6798c5ec21b48db10018f2a92 100644 (file)
--- a/include/options.h
+++ b/include/options.h
@@ -8,6 +8,8 @@ typedef struct {
   int printHeader;
   int printSegments;
   int printSections;
+  unsigned insertBeforeOffs;
+  unsigned insertBeforeSz;
 } CLIOpts;
 
 

diff --git a/src/main.c b/src/main.c
index 991fe09423b20247cfc0a4765873f3707934d3d9..4467a2cbcc995887a7ba88f4a5100e687b66f387 100644 (file)
--- a/src/main.c
+++ b/src/main.c
@@ -67,12 +67,16 @@ int main(int argc, char **argv)
 
     if (me) {
       printf("Model successfully loaded.\n");
-
       elfu_mCheck(me);
-      printf("Model checked.\n");
+      printf("Input model checked.\n");
 
-      elfu_mToElf(me, hOut.e);
+      if (opts.insertBeforeSz) {
+        elfu_mInsertBefore(me, opts.insertBeforeOffs, opts.insertBeforeSz);
+      }
 
+      elfu_mCheck(me);
+      printf("Output model checked.\n");
+      elfu_mToElf(me, hOut.e);
       printf("Model converted to ELF, ready to be written.\n");
     } else {
       printf("Failed to load model.\n");

diff --git a/src/model/insert.c b/src/model/insert.c
new file mode 100644 (file)
index 0000000..2086c6e
--- /dev/null
+++ b/src/model/insert.c
@@ -0,0 +1,111 @@
+#include <assert.h>
+#include <sys/types.h>
+#include <gelf.h>
+#include <libelfu/libelfu.h>
+
+
+
+/*
+ * Insert space at a given position in the file by moving everything
+ * after it towards the end of the file, and everything before it
+ * towards lower memory regions where it is mapped.
+ *
+ * off must not be in the middle of any data structure, such as
+ * PHDRs, SHDRs, or sections. Behaviour is undefined if it is.
+ *
+ * PHDRs will be patched such that everything AFTER off is mapped to
+ * the same address in memory, and everything BEFORE it is shifted to
+ * lower addresses, making space for the new data in-between.
+ */
+GElf_Xword elfu_mInsertBefore(ElfuElf *me, GElf_Off off, GElf_Xword size)
+{
+  ElfuScn *ms;
+  ElfuPhdr *mp;
+
+  assert(me);
+
+  // TODO: Take p_align into account
+
+  /* Move SHDRs and PHDRs */
+  if (me->ehdr.e_shoff >= off) {
+    me->ehdr.e_shoff += size;
+  }
+
+  if (me->ehdr.e_phoff >= off) {
+    me->ehdr.e_phoff += size;
+  }
+
+  /* Patch PHDRs to include new data */
+  CIRCLEQ_FOREACH(mp, &me->phdrList, elem) {
+    GElf_Off end = mp->phdr.p_offset + mp->phdr.p_filesz;
+
+    if (mp->phdr.p_offset >= off) {
+      /* Insertion before PHDR's content, so it's just shifted */
+      mp->phdr.p_offset += size;
+    } else {
+      /* mp->phdr.p_offset < off */
+
+      if (off < end) {
+        /* Mark this as a modified area */
+
+        /* Insertion in the middle of PHDR, so let it span the new data */
+        mp->phdr.p_filesz += size;
+        mp->phdr.p_memsz += size;
+        mp->phdr.p_vaddr -= size;
+        mp->phdr.p_paddr -= size;
+      } else {
+        /* Insertion after PHDR's content, so it may need to be
+           remapped. This will happen in a second pass.
+         */
+      }
+    }
+  }
+
+  /* For each LOAD header, find clashing headers that need to be
+     remapped to lower memory areas.
+   */
+  CIRCLEQ_FOREACH(mp, &me->phdrList, elem) {
+    if (mp->phdr.p_type == PT_LOAD) {
+      ElfuPhdr *mp2;
+
+      CIRCLEQ_FOREACH(mp2, &me->phdrList, elem) {
+        if (mp2->phdr.p_type != PT_LOAD
+            && mp2->phdr.p_offset + mp2->phdr.p_filesz <= off) {
+          /* The PHDR ends in the file before the injection site */
+          GElf_Off vend1 = mp->phdr.p_vaddr + mp->phdr.p_memsz;
+          GElf_Off pend1 = mp->phdr.p_paddr + mp->phdr.p_memsz;
+          GElf_Off vend2 = mp2->phdr.p_vaddr + mp2->phdr.p_memsz;
+          GElf_Off pend2 = mp2->phdr.p_paddr + mp2->phdr.p_memsz;
+
+          /* If mp and mp2 now overlap in memory */
+          if ((mp2->phdr.p_vaddr < vend1 && vend2 > mp->phdr.p_vaddr)
+              || (mp2->phdr.p_paddr < pend1 && pend2 > mp->phdr.p_paddr)) {
+            /* Move mp2 down in memory, as mp has been resized.
+               Maintaining the relative offset between them is the best
+               guess at maintaining consistency.
+             */
+            mp2->phdr.p_vaddr -= size;
+            mp2->phdr.p_paddr -= size;
+          }
+        }
+      }
+    }
+  }
+
+  /* Move the sections themselves */
+  CIRCLEQ_FOREACH(ms, &me->scnList, elem) {
+    if (ms->shdr.sh_offset >= off) {
+      ms->shdr.sh_offset += size;
+    } else {
+      /* sh_offset < off */
+
+      /* If this was in a LOAD segment, it has been adjusted there
+         and this synchronises it.
+         If not, it doesn't matter anyway.
+       */
+      ms->shdr.sh_addr -= size;
+    }
+  }
+
+  return size;
+}

diff --git a/src/options.c b/src/options.c
index 1b258fe3e86736b3fe8448caf29869fb8777e3dc..55a91c553bfb219beef058c0c824ddc554194b5a 100644 (file)
--- a/src/options.c
+++ b/src/options.c
@@ -11,13 +11,14 @@ static void printUsage(char *progname)
   printf("Usage: %s [OPTIONS] <elf-file>\n", progname);
   printf("\n"
           "Options:\n"
-          "  -h, --help                 Print this help message\n"
-          "  -o, --output               Where to write the modified ELF file to\n"
+          "  -h, --help                     Print this help message\n"
+          "  -o, --output                   Where to write the modified ELF file to\n"
           "\n"
-          "      --print-header         Print ELF header\n"
-          "      --print-segments       Print program headers\n"
-          "      --print-sections       Print sections\n"
+          "      --print-header             Print ELF header\n"
+          "      --print-segments           Print program headers\n"
+          "      --print-sections           Print sections\n"
           "\n"
+          "      --insert-before off,sz     Insert spacing at given offset\n"
           "\n");
 }
 
@@ -28,6 +29,7 @@ void parseOptions(CLIOpts *opts, int argc, char **argv)
   char *progname = argv[0];
   int c;
   int option_index = 0;
+  char *endptr;
 
   static struct option long_options[] = {
     {"help", 0, 0, 'h'},
@@ -35,6 +37,7 @@ void parseOptions(CLIOpts *opts, int argc, char **argv)
     {"print-header", 0, 0, 10001},
     {"print-segments", 0, 0, 10002},
     {"print-sections", 0, 0, 10003},
+    {"insert-before", 1, 0, 10004},
     {NULL, 0, NULL, 0}
   };
 
@@ -56,6 +59,16 @@ void parseOptions(CLIOpts *opts, int argc, char **argv)
       case 10003:
         opts->printSections = 1;
         break;
+      case 10004:
+        opts->insertBeforeOffs = strtoul(optarg, &endptr, 0);
+        if (endptr[0] != ',') {
+          goto USAGE;
+        }
+        opts->insertBeforeSz = strtoul(endptr + 1, &endptr, 0);
+        if (endptr[0] != '\0' || opts->insertBeforeSz == 0) {
+          goto USAGE;
+        }
+        break;
       case '?':
       default:
         goto USAGE;