[PATCH] D123985: [ELF] Error on invalid GOT or PLT relocations

[Shoaib Meenai via Phabricator via llvm-commits]

smeenai created this revision.
smeenai added a reviewer: MaskRay.
Herald added subscribers: StephenFan, arichardson, emaste.
Herald added a project: All.
smeenai requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

Because of https://llvm.org/PR50675, we can end up producing a PLT
relocation referencing a symbol that's dropped from the dynamic symbol
table, which in turn causes a crash at runtime. We ran into this again
recently, resulting in crashes for our users. Rather than silently
producing a binary that will crash at runtime, error out if we attempt
to produce a GOT or PLT relocation against a symbol not in the dynamic
symbol table.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D123985

Files:
  lld/ELF/SyntheticSections.cpp
  lld/test/ELF/invalid-plt-relocation.test


Index: lld/test/ELF/invalid-plt-relocation.test
===================================================================
--- /dev/null
+++ lld/test/ELF/invalid-plt-relocation.test
@@ -0,0 +1,32 @@
+# REQUIRES: x86
+
+# RUN: rm -rf %t && split-file %s %t
+# RUN: llvm-mc -triple x86_64-linux-gnu --filetype=obj -o %t/unwind.o %t/unwind.s
+# RUN: ld.lld -shared -o %t/libunwind.so %t/unwind.o
+# RUN: llvm-as -o %t/resume.bc %t/resume.ll
+# RUN: not ld.lld -shared -o %t/libresume.so %t/resume.bc %t/libunwind.so \
+# RUN:   --gc-sections --wrap _Unwind_Resume 2>&1 | FileCheck %s
+
+# CHECK: error: PLT relocation references symbol not present in dynamic symbol table: __wrap__Unwind_Resume
+
+#--- unwind.s
+.globl _Unwind_Resume
+.globl __wrap__Unwind_Resume
+_Unwind_Resume:
+__wrap__Unwind_Resume:
+        retq
+
+#--- resume.ll
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+define dso_local void @_Z1fv() optnone noinline personality i8* bitcast (void ()* @throw to i8*) {
+  invoke void @throw()
+          to label %unreachable unwind label %lpad
+lpad:
+  %1 = landingpad { i8*, i32 }
+          cleanup
+  resume { i8*, i32 } %1
+unreachable:
+  unreachable
+}
+declare void @throw()
Index: lld/ELF/SyntheticSections.cpp
===================================================================
--- lld/ELF/SyntheticSections.cpp
+++ lld/ELF/SyntheticSections.cpp
@@ -1589,8 +1589,15 @@
 }
 
 uint32_t DynamicReloc::getSymIndex(SymbolTableBaseSection *symTab) const {
-  if (needsDynSymIndex())
-    return symTab->getSymbolIndex(sym);
+  if (needsDynSymIndex()) {
+    size_t index = symTab->getSymbolIndex(sym);
+    if (index == 0 && (type == target->gotRel || type == target->pltRel))
+      error(Twine(type == target->gotRel ? "GOT" : "PLT") +
+            " relocation references symbol not present in dynamic "
+            "symbol table: " +
+            toString(*sym));
+    return index;
+  }
   return 0;
 }
 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D123985.423541.patch
Type: text/x-patch
Size: 2013 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20220419/26ab7a5d/attachment.bin>