[PATCH] D43819: [ELF] - Restrict section offsets that exceeds file size.

[George Rimar via Phabricator via llvm-commits]

grimar updated this revision to Diff 136264.
grimar marked 7 inline comments as done.
grimar added a comment.

- Addressed review comments.


https://reviews.llvm.org/D43819

Files:
  ELF/Writer.cpp
  test/ELF/linkerscript/sections-va-overflow.s


Index: test/ELF/linkerscript/sections-va-overflow.s
===================================================================
--- test/ELF/linkerscript/sections-va-overflow.s
+++ test/ELF/linkerscript/sections-va-overflow.s
@@ -0,0 +1,18 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
+# RUN: echo "PHDRS{  ph_headers  PT_PHDR PHDRS;" > %t.script
+# RUN: echo "ph_text PT_LOAD FILEHDR PHDRS  FLAGS (0x1 | 0x4); }" >> %t.script
+# RUN: echo "SECTIONS { . = 0xffffffff20000000;" >> %t.script
+# RUN: echo "  .text : { *(.text*) } : ph_text " >> %t.script
+# RUN: echo "  .test 0x1000 : { BYTE(0) } }" >> %t.script
+# RUN: not ld.lld -o %t.so --script %t.script %t.o 2>&1 | FileCheck %s -check-prefix=ERR
+
+## Section .test has VA 0x1000 and placed in the same segment as section .text
+## with VA 0xffffffff20000000. That might be technically correct, but most probably
+## is a result of a broken script file and causes file offset calculation overflow.
+## It seems we do not have to support it, so we don't and we report an error in this case.
+# ERR: error: unable to place section .text at file offset [0xFFFFFFFF20000000 -> 0xFFFFFFFE40000000]; check your linker script for overflows
+
+.global _start
+_start:
+  retq
Index: ELF/Writer.cpp
===================================================================
--- ELF/Writer.cpp
+++ ELF/Writer.cpp
@@ -1823,6 +1823,12 @@
   }
 }
 
+static std::string rangeToString(uint64_t Addr, uint64_t Len) {
+  if (Len == 0)
+    return "<empty range at 0x" + utohexstr(Addr) + ">";
+  return "[0x" + utohexstr(Addr) + " -> 0x" + utohexstr(Addr + Len - 1) + "]";
+}
+
 // Adjusts the file alignment for a given output section and returns
 // its new file offset. The file offset must be the same with its
 // virtual address (modulo the page size) so that the loader can load
@@ -1893,6 +1899,18 @@
 
   SectionHeaderOff = alignTo(Off, Config->Wordsize);
   FileSize = SectionHeaderOff + (OutputSections.size() + 1) * sizeof(Elf_Shdr);
+
+  // It is possible to get file offset overlaps or overflows with linker
+  // scripts. We perform checks required in checkNoOverlappingSections() and
+  // want to prevent file size overflows here because it would crash the linker.
+  for (OutputSection *Sec : OutputSections) {
+    if (Sec->Type == SHT_NOBITS)
+      continue;
+    if ((Sec->Offset >= FileSize) || (Sec->Offset + Sec->Size >= FileSize))
+      error("unable to place section " + Sec->Name + " at file offset " +
+            rangeToString(Sec->Offset, Sec->Offset + Sec->Size) +
+            "; check your linker script for overflows");
+  }
 }
 
 // Finalize the program headers. We call this function after we assign
@@ -1931,12 +1949,6 @@
   }
 }
 
-static std::string rangeToString(uint64_t Addr, uint64_t Len) {
-  if (Len == 0)
-    return "<empty range at 0x" + utohexstr(Addr) + ">";
-  return "[0x" + utohexstr(Addr) + " -> 0x" + utohexstr(Addr + Len - 1) + "]";
-}
-
 // Check whether sections overlap for a specific address range (file offsets,
 // load and virtual adresses).
 //


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