From 36d0f928c6e78747ffb122372d4d94d97fd0a193 Mon Sep 17 00:00:00 2001
From: Christian Blichmann <cblichmann@google.com>
Date: Fri, 11 Feb 2022 07:19:01 -0800
Subject: [PATCH] Apply page offset during stack unwinding/symbolization

This fixes a couple of tests in the open source version of the code.
Internally, since we are using a different ELF loader, the page offset
will always be zero. Hence we never notices this was broken.

PiperOrigin-RevId: 427996428
Change-Id: I44c5b5610b074cf69b9f0c5eeb051be50923e351
---
 sandboxed_api/sandbox2/unwind/unwind.cc     |  6 ++++--
 sandboxed_api/sandbox2/util/minielf_test.cc | 17 +++++++++--------
 2 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/sandboxed_api/sandbox2/unwind/unwind.cc b/sandboxed_api/sandbox2/unwind/unwind.cc
index ddeaba0..e62a458 100644
--- a/sandboxed_api/sandbox2/unwind/unwind.cc
+++ b/sandboxed_api/sandbox2/unwind/unwind.cc
@@ -177,8 +177,10 @@ absl::StatusOr<SymbolMap> LoadSymbolsMap(pid_t pid) {
 
     for (const ElfFile::Symbol& symbol : elf->symbols()) {
       if (elf->position_independent()) {
-        if (symbol.address < entry.end - entry.start) {
-          addr_to_symbol[symbol.address + entry.start] = symbol.name;
+        if (symbol.address >= entry.pgoff &&
+            symbol.address - entry.pgoff < entry.end - entry.start) {
+          addr_to_symbol[symbol.address + entry.start - entry.pgoff] =
+              symbol.name;
         }
       } else {
         if (symbol.address >= entry.start && symbol.address < entry.end) {
diff --git a/sandboxed_api/sandbox2/util/minielf_test.cc b/sandboxed_api/sandbox2/util/minielf_test.cc
index 1e973c3..cccd97f 100644
--- a/sandboxed_api/sandbox2/util/minielf_test.cc
+++ b/sandboxed_api/sandbox2/util/minielf_test.cc
@@ -26,13 +26,14 @@
 #include "sandboxed_api/util/file_helpers.h"
 #include "sandboxed_api/util/status_matchers.h"
 
-extern "C" void ExportedFunctionName() {
+extern "C" void ExportedFunction() {
   // Don't do anything - used to generate a symbol.
 }
 
 namespace file = ::sapi::file;
 using ::sapi::GetTestSourcePath;
 using ::sapi::IsOk;
+using ::testing::ElementsAre;
 using ::testing::Eq;
 using ::testing::IsTrue;
 using ::testing::Ne;
@@ -65,19 +66,20 @@ TEST(MinielfTest, SymbolResolutionWorks) {
                             ParseProcMaps(maps_buffer));
 
   // Find maps entry that covers this entry.
-  uint64_t function_address = reinterpret_cast<uint64_t>(ExportedFunctionName);
-  auto function_entry =
+  uint64_t function_address = reinterpret_cast<uint64_t>(&ExportedFunction);
+  auto entry =
       absl::c_find_if(maps, [function_address](const MapsEntry& entry) {
         return entry.start <= function_address && entry.end > function_address;
       });
-  ASSERT_THAT(function_entry, Ne(maps.end()));
-  function_address -= function_entry->start;
+  ASSERT_THAT(entry, Ne(maps.end()));
 
   auto function_symbol =
       absl::c_find_if(elf.symbols(), [](const ElfFile::Symbol& symbol) {
-        return symbol.name == "ExportedFunctionName";
+        return symbol.name == "ExportedFunction";
       });
   ASSERT_THAT(function_symbol, Ne(elf.symbols().end()));
+
+  function_address -= entry->start - entry->pgoff;
   EXPECT_THAT(function_symbol->address, Eq(function_address));
 }
 
@@ -86,8 +88,7 @@ TEST(MinielfTest, ImportedLibraries) {
       ElfFile elf, ElfFile::ParseFromFile(
                        GetTestSourcePath("sandbox2/util/testdata/hello_world"),
                        ElfFile::kLoadImportedLibraries));
-  std::vector<std::string> imported_libraries = {"libc.so.6"};
-  EXPECT_THAT(elf.imported_libraries(), Eq(imported_libraries));
+  EXPECT_THAT(elf.imported_libraries(), ElementsAre("libc.so.6"));
 }
 
 }  // namespace