From de0fb393ae8136a5958fe17eee0c6285e2f7f91a Mon Sep 17 00:00:00 2001
From: Dmitriy Ivanov <dimitry@google.com>
Date: Sun, 26 Jul 2015 07:37:09 -0700
Subject: [PATCH] Restore protection flags for ifunc during relocs.

IFUNC relocations require executable flag for the load
segment containing .text. When dso has text relocs linker
removes exec which causes crash during ifunc relocations.

This patch fixes this problem by restoring segments protection
for ifunc relocs.

Bug: http://b/22611399
Change-Id: Icbf3be0fec0e42bf805bcad7533e2032a2e11b9c
---
 linker/linker.cpp | 54 ++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 51 insertions(+), 3 deletions(-)

diff --git a/linker/linker.cpp b/linker/linker.cpp
index e84036a5f..b860f70b9 100644
--- a/linker/linker.cpp
+++ b/linker/linker.cpp
@@ -1921,9 +1921,32 @@ bool soinfo::relocate(const VersionTracker& version_tracker, ElfRelIteratorT&& r
             DL_ERR("unknown weak reloc type %d @ %p (%zu)", type, rel, idx);
             return false;
         }
-      } else {
-        // We got a definition.
+      } else { // We got a definition.
+#if !defined(__LP64__)
+        // When relocating dso with text_relocation .text segment is
+        // not executable. We need to restore elf flags before resolving
+        // STT_GNU_IFUNC symbol.
+        bool protect_segments = has_text_relocations &&
+                                lsi == this &&
+                                ELF_ST_TYPE(s->st_info) == STT_GNU_IFUNC;
+        if (protect_segments) {
+          if (phdr_table_protect_segments(phdr, phnum, load_bias) < 0) {
+            DL_ERR("can't protect segments for \"%s\": %s",
+                   get_realpath(), strerror(errno));
+            return false;
+          }
+        }
+#endif
         sym_addr = lsi->resolve_symbol_address(s);
+#if !defined(__LP64__)
+        if (protect_segments) {
+          if (phdr_table_unprotect_segments(phdr, phnum, load_bias) < 0) {
+            DL_ERR("can't unprotect loadable segments for \"%s\": %s",
+                   get_realpath(), strerror(errno));
+            return false;
+          }
+        }
+#endif
       }
       count_relocation(kRelocSymbol);
     }
@@ -1960,7 +1983,32 @@ bool soinfo::relocate(const VersionTracker& version_tracker, ElfRelIteratorT&& r
         TRACE_TYPE(RELO, "RELO IRELATIVE %16p <- %16p\n",
                     reinterpret_cast<void*>(reloc),
                     reinterpret_cast<void*>(load_bias + addend));
-        *reinterpret_cast<ElfW(Addr)*>(reloc) = call_ifunc_resolver(load_bias + addend);
+        {
+#if !defined(__LP64__)
+          // When relocating dso with text_relocation .text segment is
+          // not executable. We need to restore elf flags for this
+          // particular call.
+          if (has_text_relocations) {
+            if (phdr_table_protect_segments(phdr, phnum, load_bias) < 0) {
+              DL_ERR("can't protect segments for \"%s\": %s",
+                     get_realpath(), strerror(errno));
+              return false;
+            }
+          }
+#endif
+          ElfW(Addr) ifunc_addr = call_ifunc_resolver(load_bias + addend);
+#if !defined(__LP64__)
+          // Unprotect it afterwards...
+          if (has_text_relocations) {
+            if (phdr_table_unprotect_segments(phdr, phnum, load_bias) < 0) {
+              DL_ERR("can't unprotect loadable segments for \"%s\": %s",
+                     get_realpath(), strerror(errno));
+              return false;
+            }
+          }
+#endif
+          *reinterpret_cast<ElfW(Addr)*>(reloc) = ifunc_addr;
+        }
         break;
 
 #if defined(__aarch64__)