Revert "Remove text-relocation support for lp32"

This reverts commit cb00add1b3.

Bug: 20020312
Bug: 20013628
Change-Id: I8baa3d4b6c7fef50c9e2531257d5b96762099eb3

linker/linker.cpp

@@ -2297,8 +2297,13 @@ bool soinfo::prelink_image() {
         break;
 
       case DT_TEXTREL:
-        DL_ERR("text relocations (DT_TEXTREL) found in the ELF file \"%s\"", name);
+#if defined(__LP64__)
+        DL_ERR("text relocations (DT_TEXTREL) found in 64-bit ELF file \"%s\"", name);
         return false;
+#else
+        has_text_relocations = true;
+        break;
+#endif
 
       case DT_SYMBOLIC:
         has_DT_SYMBOLIC = true;
@@ -2310,8 +2315,12 @@ bool soinfo::prelink_image() {
 
       case DT_FLAGS:
         if (d->d_un.d_val & DF_TEXTREL) {
-          DL_ERR("text relocations (DF_TEXTREL) found in the ELF file \"%s\"", name);
+#if defined(__LP64__)
+          DL_ERR("text relocations (DF_TEXTREL) found in 64-bit ELF file \"%s\"", name);
           return false;
+#else
+          has_text_relocations = true;
+#endif
         }
         if (d->d_un.d_val & DF_SYMBOLIC) {
           has_DT_SYMBOLIC = true;
@@ -2420,6 +2429,20 @@ bool soinfo::link_image(const soinfo_list_t& global_group, const soinfo_list_t&
     local_group_root_ = this;
   }
 
+#if !defined(__LP64__)
+  if (has_text_relocations) {
+    // Make segments writable to allow text relocations to work properly. We will later call
+    // phdr_table_protect_segments() after all of them are applied and all constructors are run.
+    DL_WARN("%s has text relocations. This is wasting memory and prevents "
+            "security hardening. Please fix.", name);
+    if (phdr_table_unprotect_segments(phdr, phnum, load_bias) < 0) {
+      DL_ERR("can't unprotect loadable segments for \"%s\": %s",
+             name, strerror(errno));
+      return false;
+    }
+  }
+#endif
+
   if (android_relocs_ != nullptr) {
     // check signature
     if (android_relocs_size_ > 3 &&
@@ -2490,6 +2513,17 @@ bool soinfo::link_image(const soinfo_list_t& global_group, const soinfo_list_t&
 
   DEBUG("[ finished linking %s ]", name);
 
+#if !defined(__LP64__)
+  if (has_text_relocations) {
+    // All relocations are done, we can protect our segments back to read-only.
+    if (phdr_table_protect_segments(phdr, phnum, load_bias) < 0) {
+      DL_ERR("can't protect segments for \"%s\": %s",
+             name, strerror(errno));
+      return false;
+    }
+  }
+#endif
+
   /* We can also turn on GNU RELRO protection */
   if (phdr_table_protect_gnu_relro(phdr, phnum, load_bias) < 0) {
     DL_ERR("can't enable GNU RELRO protection for \"%s\": %s",

linker/linker.h

@@ -226,8 +226,8 @@ struct soinfo {
   // value to get the corresponding address in the process' address space.
   ElfW(Addr) load_bias;
 
-#if defined(__arm__)
-  bool unused4; // DO NOT USE, maintained for compatibility
+#if !defined(__LP64__)
+  bool has_text_relocations;
 #endif
   bool has_DT_SYMBOLIC;
 

linker/linker_phdr.cpp

@@ -412,6 +412,70 @@ bool ElfReader::LoadSegments() {
   return true;
 }
 
+/* Used internally. Used to set the protection bits of all loaded segments
+ * with optional extra flags (i.e. really PROT_WRITE). Used by
+ * phdr_table_protect_segments and phdr_table_unprotect_segments.
+ */
+static int _phdr_table_set_load_prot(const ElfW(Phdr)* phdr_table, size_t phdr_count,
+                                     ElfW(Addr) load_bias, int extra_prot_flags) {
+  const ElfW(Phdr)* phdr = phdr_table;
+  const ElfW(Phdr)* phdr_limit = phdr + phdr_count;
+
+  for (; phdr < phdr_limit; phdr++) {
+    if (phdr->p_type != PT_LOAD || (phdr->p_flags & PF_W) != 0) {
+      continue;
+    }
+
+    ElfW(Addr) seg_page_start = PAGE_START(phdr->p_vaddr) + load_bias;
+    ElfW(Addr) seg_page_end   = PAGE_END(phdr->p_vaddr + phdr->p_memsz) + load_bias;
+
+    int ret = mprotect(reinterpret_cast<void*>(seg_page_start),
+                       seg_page_end - seg_page_start,
+                       PFLAGS_TO_PROT(phdr->p_flags) | extra_prot_flags);
+    if (ret < 0) {
+      return -1;
+    }
+  }
+  return 0;
+}
+
+/* Restore the original protection modes for all loadable segments.
+ * You should only call this after phdr_table_unprotect_segments and
+ * applying all relocations.
+ *
+ * Input:
+ *   phdr_table  -> program header table
+ *   phdr_count  -> number of entries in tables
+ *   load_bias   -> load bias
+ * Return:
+ *   0 on error, -1 on failure (error code in errno).
+ */
+int phdr_table_protect_segments(const ElfW(Phdr)* phdr_table,
+                                size_t phdr_count, ElfW(Addr) load_bias) {
+  return _phdr_table_set_load_prot(phdr_table, phdr_count, load_bias, 0);
+}
+
+/* Change the protection of all loaded segments in memory to writable.
+ * This is useful before performing relocations. Once completed, you
+ * will have to call phdr_table_protect_segments to restore the original
+ * protection flags on all segments.
+ *
+ * Note that some writable segments can also have their content turned
+ * to read-only by calling phdr_table_protect_gnu_relro. This is no
+ * performed here.
+ *
+ * Input:
+ *   phdr_table  -> program header table
+ *   phdr_count  -> number of entries in tables
+ *   load_bias   -> load bias
+ * Return:
+ *   0 on error, -1 on failure (error code in errno).
+ */
+int phdr_table_unprotect_segments(const ElfW(Phdr)* phdr_table,
+                                  size_t phdr_count, ElfW(Addr) load_bias) {
+  return _phdr_table_set_load_prot(phdr_table, phdr_count, load_bias, PROT_WRITE);
+}
+
 /* Used internally by phdr_table_protect_gnu_relro and
  * phdr_table_unprotect_gnu_relro.
  */

linker/linker_phdr.h

@@ -84,6 +84,12 @@ class ElfReader {
 size_t phdr_table_get_load_size(const ElfW(Phdr)* phdr_table, size_t phdr_count,
                                 ElfW(Addr)* min_vaddr = nullptr, ElfW(Addr)* max_vaddr = nullptr);
 
+int phdr_table_protect_segments(const ElfW(Phdr)* phdr_table,
+                                size_t phdr_count, ElfW(Addr) load_bias);
+
+int phdr_table_unprotect_segments(const ElfW(Phdr)* phdr_table, size_t phdr_count,
+                                  ElfW(Addr) load_bias);
+
 int phdr_table_protect_gnu_relro(const ElfW(Phdr)* phdr_table, size_t phdr_count,
                                  ElfW(Addr) load_bias);