[PATCH 2/2] Allow targets to reenable support for non-PIE executables

0002-Allow-targets-to-reenable-support-for-non-PIE-execut.patch

From 989a14bfb86608aba038b6786a3ab312bd7aeb6e Mon Sep 17 00:00:00 2001
From: Steven Luo <[email protected]>
Date: Sat, 15 Nov 2014 17:58:48 -0800
Subject: [PATCH 2/2] Allow targets to reenable support for non-PIE
 executables

Many legacy devices have non-PIE binary blob executables which are never
going to be updated by the manufacturer; allow the dynamic linker to
load these executables so that they can work.

This rolls back the following commit:

  Cleanup: updated comments
  * 6275f2083415d22a6ce0de55645079cd47e0cc80

Allows targets to reenable this code:

  Cleanup: remove AARCH/ARM_COPY relocation support
  * b906e13c55c9fe9b4157ba548534a0230434882b

And allows targets to disable this behavior if necessary:

  Remove support for non-PIE executables
  * 2aebf5429bb1241a3298b5b642d38f73124c2026

Derived from AOSP Change-Id Ia2501aa14bd30feb4a6ce66bdb7c9f066dba0b5f.

[[email protected]: update for Android 5.1+]
---
 linker/Android.mk |    4 ++++
 linker/linker.cpp |   62 +++++++++++++++++++++++++++++++++++++++++++----------
 2 files changed, 55 insertions(+), 11 deletions(-)

diff --git a/linker/Android.mk b/linker/Android.mk
index 4298032..84cba0f 100644
--- a/linker/Android.mk
+++ b/linker/Android.mk
@@ -39,6 +39,10 @@ LOCAL_CPPFLAGS += \
 # We need to access Bionic private headers in the linker.
 LOCAL_CFLAGS += -I$(LOCAL_PATH)/../libc/
 
+ifeq ($(TARGET_ALLOW_NON_PIE_EXECUTABLES),true)
+	LOCAL_CFLAGS += -DTARGET_ALLOW_NON_PIE_EXECUTABLES
+endif
+
 # we don't want crtbegin.o (because we have begin.o), so unset it
 # just for this module
 LOCAL_NO_CRT := true
diff --git a/linker/linker.cpp b/linker/linker.cpp
index 789040b..c7ef897 100644
--- a/linker/linker.cpp
+++ b/linker/linker.cpp
@@ -63,6 +63,7 @@
  *
  * open issues / todo:
  *
+ * - are we doing everything we should for ARM_COPY relocations?
  * - cleaner error reporting
  * - after linking, set as much stuff as possible to READONLY
  *   and NOEXEC
@@ -1469,17 +1470,52 @@ int soinfo::Relocate(ElfW(Rel)* rel, unsigned count) {
         *reinterpret_cast<ElfW(Addr)*>(reloc) += sym_addr - rel->r_offset;
         break;
       case R_ARM_COPY:
-        /*
-         * ET_EXEC is not supported so this should not happen.
-         *
-         * http://infocenter.arm.com/help/topic/com.arm.doc.ihi0044d/IHI0044D_aaelf.pdf
-         *
-         * Section 4.7.1.10 "Dynamic relocations"
-         * R_ARM_COPY may only appear in executable objects where e_type is
-         * set to ET_EXEC.
-         */
-        DL_ERR("%s R_ARM_COPY relocations are not supported", name);
-        return -1;
+#ifdef TARGET_ALLOW_NON_PIE_EXECUTABLES
+        if ((flags & FLAG_EXE) == 0) {
+#endif
+          /*
+           * http://infocenter.arm.com/help/topic/com.arm.doc.ihi0044d/IHI0044D_aaelf.pdf
+           *
+           * Section 4.7.1.10 "Dynamic relocations"
+           * R_ARM_COPY may only appear in executable objects where e_type is
+           * set to ET_EXEC.
+           *
+           * TODO: FLAG_EXE is set for both ET_DYN and ET_EXEC executables.
+           * We should explicitly disallow ET_DYN executables from having
+           * R_ARM_COPY relocations.
+           */
+          DL_ERR("%s R_ARM_COPY relocations only supported for ET_EXEC", name);
+          return -1;
+#ifdef TARGET_ALLOW_NON_PIE_EXECUTABLES
+        }
+        count_relocation(kRelocCopy);
+        MARK(rel->r_offset);
+        TRACE_TYPE(RELO, "RELO %08x <- %d @ %08x %s", reloc, s->st_size, sym_addr, sym_name);
+        if (reloc == sym_addr) {
+          ElfW(Sym)* src = __soinfo_do_lookup(this, sym_name, &lsi, false);
+
+          if (src == NULL) {
+            DL_ERR("%s R_ARM_COPY relocation source cannot be resolved", name);
+            return -1;
+          }
+          if (lsi->has_DT_SYMBOLIC) {
+            DL_ERR("%s invalid R_ARM_COPY relocation against DT_SYMBOLIC shared "
+                   "library %s (built with -Bsymbolic?)", name, lsi->name);
+            return -1;
+          }
+          if (s->st_size < src->st_size) {
+            DL_ERR("%s R_ARM_COPY relocation size mismatch (%d < %d)",
+                   name, s->st_size, src->st_size);
+            return -1;
+          }
+          memcpy(reinterpret_cast<void*>(reloc),
+                 reinterpret_cast<void*>(src->st_value + lsi->load_bias), src->st_size);
+        } else {
+          DL_ERR("%s R_ARM_COPY relocation target cannot be resolved", name);
+          return -1;
+        }
+        break;
+#endif /* TARGET_ALLOW_NON_PIE_EXECUTABLES */
 #elif defined(__i386__)
       case R_386_JMP_SLOT:
         count_relocation(kRelocAbsolute);
@@ -2407,8 +2443,12 @@ static ElfW(Addr) __linker_init_post_relocation(KernelArgumentBlock& args, ElfW(
 
   ElfW(Ehdr)* elf_hdr = reinterpret_cast<ElfW(Ehdr)*>(si->base);
   if (elf_hdr->e_type != ET_DYN) {
+#ifdef TARGET_ALLOW_NON_PIE_EXECUTABLES
+    __libc_format_fd(2, "WARNING: legacy non-PIE executable, ASLR disabled\n");
+#else
     __libc_format_fd(2, "error: only position independent executables (PIE) are supported.\n");
     exit(EXIT_FAILURE);
+#endif
   }
 
   // Use LD_LIBRARY_PATH and LD_PRELOAD (but only if we aren't setuid/setgid).
-- 
1.7.10.4