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

0001-Allow-targets-to-reenable-support-for-non-PIE-execut.patch

From eba25085e5d1a44b595d0439d350a3e6b4a0684f Mon Sep 17 00:00:00 2001
From: Steven Luo <[email protected]>
Date: Sat, 15 Nov 2014 17:58:48 -0800
Subject: [PATCH] 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 commits:

  Cleanup: updated comments
  * 6275f2083415d22a6ce0de55645079cd47e0cc80
  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.
---
 linker/Android.mk |    4 ++
 linker/linker.cpp |  115 +++++++++++++++++++++++++++++++++++++++++++----------
 2 files changed, 97 insertions(+), 22 deletions(-)

diff --git a/linker/Android.mk b/linker/Android.mk
index 5853c90..14cee90 100644
--- a/linker/Android.mk
+++ b/linker/Android.mk
@@ -38,6 +38,10 @@ 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 cf65705..3f0ba92 100644
--- a/linker/linker.cpp
+++ b/linker/linker.cpp
@@ -60,6 +60,7 @@
  *
  * 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
@@ -1117,17 +1118,52 @@ static int soinfo_relocate(soinfo* si, ElfW(Rela)* rela, unsigned count, soinfo*
         break;
 
     case R_AARCH64_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_AARCH64_COPY may only appear in executable objects where e_type is
-         * set to ET_EXEC.
-         */
-        DL_ERR("%s R_AARCH64_COPY relocations are not supported", si->name);
-        return -1;
+        if ((si->flags & FLAG_EXE) == 0) {
+            /*
+              * http://infocenter.arm.com/help/topic/com.arm.doc.ihi0044d/IHI0044D_aaelf.pdf
+              *
+              * Section 4.7.1.10 "Dynamic relocations"
+              * R_AARCH64_COPY may only appear in executable objects where e_type is
+              * set to ET_EXEC.
+              *
+              * FLAG_EXE is set for both ET_DYN and ET_EXEC executables.
+              * We should explicitly disallow ET_DYN executables from having
+              * R_AARCH64_COPY relocations.
+              */
+            DL_ERR("%s R_AARCH64_COPY relocations only supported for ET_EXEC", si->name);
+            return -1;
+        }
+        count_relocation(kRelocCopy);
+        MARK(rela->r_offset);
+        TRACE_TYPE(RELO, "RELO COPY %16llx <- %lld @ %16llx %s\n",
+                   reloc,
+                   s->st_size,
+                   (sym_addr + rela->r_addend),
+                   sym_name);
+        if (reloc == (sym_addr + rela->r_addend)) {
+            ElfW(Sym)* src = soinfo_do_lookup(NULL, sym_name, &lsi, needed);
+
+            if (src == NULL) {
+                DL_ERR("%s R_AARCH64_COPY relocation source cannot be resolved", si->name);
+                return -1;
+            }
+            if (lsi->has_DT_SYMBOLIC) {
+                DL_ERR("%s invalid R_AARCH64_COPY relocation against DT_SYMBOLIC shared "
+                       "library %s (built with -Bsymbolic?)", si->name, lsi->name);
+                return -1;
+            }
+            if (s->st_size < src->st_size) {
+                DL_ERR("%s R_AARCH64_COPY relocation size mismatch (%lld < %lld)",
+                       si->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_AARCH64_COPY relocation target cannot be resolved", si->name);
+            return -1;
+        }
+        break;
     case R_AARCH64_TLS_TPREL64:
         TRACE_TYPE(RELO, "RELO TLS_TPREL64 *** %16llx <- %16llx - %16llx\n",
                    reloc, (sym_addr + rela->r_addend), rela->r_offset);
@@ -1305,17 +1341,48 @@ static int soinfo_relocate(soinfo* si, ElfW(Rel)* rel, unsigned count, soinfo* n
             *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", si->name);
-            return -1;
+            if ((si->flags & FLAG_EXE) == 0) {
+                /*
+                 * 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", si->name);
+                return -1;
+            }
+            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(NULL, sym_name, &lsi, needed);
+
+                if (src == NULL) {
+                    DL_ERR("%s R_ARM_COPY relocation source cannot be resolved", si->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?)", si->name, lsi->name);
+                    return -1;
+                }
+                if (s->st_size < src->st_size) {
+                    DL_ERR("%s R_ARM_COPY relocation size mismatch (%d < %d)",
+                           si->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", si->name);
+                return -1;
+            }
+            break;
 #elif defined(__i386__)
         case R_386_JMP_SLOT:
             count_relocation(kRelocAbsolute);
@@ -2179,8 +2246,12 @@ 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

My git on my phone displays an error like this :error Only position independent executetable (PIE) are supported.