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Flush changes to memory-mapped files once zucchini is done updating them
This patch ensures proper flushing to disk and invalidation of metadata once
the zucchini algorithm is done updating a file. These memory-mapped files were
being unmapped without first calling msync() or FlushViewOfFile(), causing
dirty pages to not be properly flushed to disk and metadata not being
invalidated.
On all platforms, flushing to disk ensures better resilience against unexpected
events like system crashes or power cuts. On macOS, this also fixes a critical
issue where the kernel skipped recomputing per-page code signatures for the
modified files. When code later tried to load these patched libraries, the
kernel would detect signature mismatches and kill the process, causing Firefox
to crash when launched after a zucchini-based update.
---
base/files/memory_mapped_file.h | 6 +++++
base/files/memory_mapped_file_posix.cc | 27 +++++++++++++++++++
base/files/memory_mapped_file_win.cc | 22 +++++++++++++++
components/zucchini/mapped_file.cc | 10 +++++++
components/zucchini/mapped_file.h | 6 +++++
5 files changed, 71 insertions(+)
diff --git a/base/files/memory_mapped_file.h b/base/files/memory_mapped_file.h
index 542403c713af..44ee14dec8f5 100644
--- a/base/files/memory_mapped_file.h
+++ b/base/files/memory_mapped_file.h
@@ -114,6 +114,12 @@ class BASE_EXPORT MemoryMappedFile {
// Is file_ a valid file handle that points to an open, memory mapped file?
bool IsValid() const;
+#if defined(MOZ_ZUCCHINI)
+ // Flushes memory-mapped changes to disk. Returns true on success, false on
+ // error. Must be called before unmapping if changes need to be persisted.
+ bool Flush();
+#endif // MOZ_ZUCCHINI
+
private:
// Given the arbitrarily aligned memory region [start, size], returns the
// boundaries of the region aligned to the granularity specified by the OS,
diff --git a/base/files/memory_mapped_file_posix.cc b/base/files/memory_mapped_file_posix.cc
index be5084bb429a..e6f624cc9eaa 100644
--- a/base/files/memory_mapped_file_posix.cc
+++ b/base/files/memory_mapped_file_posix.cc
@@ -85,9 +85,18 @@ bool MemoryMappedFile::MapFileRegionToMemory(
break;
}
+#if defined(MOZ_ZUCCHINI)
+ auto* data = static_cast<uint8_t*>(mmap(nullptr, map_size, flags, MAP_SHARED,
+ file_.GetPlatformFile(), map_start));
+ if (data != MAP_FAILED) {
+ data_ = data;
+ }
+ else {
+#else
data_ = static_cast<uint8_t*>(mmap(nullptr, map_size, flags, MAP_SHARED,
file_.GetPlatformFile(), map_start));
if (data_ == MAP_FAILED) {
+#endif // MOZ_ZUCCHINI
DPLOG(ERROR) << "mmap " << file_.GetPlatformFile();
return false;
}
@@ -107,4 +116,22 @@ void MemoryMappedFile::CloseHandles() {
length_ = 0;
}
+#if defined(MOZ_ZUCCHINI)
+bool MemoryMappedFile::Flush() {
+ if (!data_) {
+ return false;
+ }
+
+ // Synchronize memory-mapped changes to disk. MS_SYNC ensures all writes are
+ // completed before returning. MS_INVALIDATE is critical on macOS to
+ // invalidate kernel code signing caches, ensuring subsequent opens will
+ // revalidate signatures.
+ bool success = msync(data_, length_, MS_SYNC | MS_INVALIDATE) == 0;
+ if (!success) {
+ PLOG(ERROR) << "msync failed";
+ }
+ return success;
+}
+#endif // MOZ_ZUCCHINI
+
} // namespace base
diff --git a/base/files/memory_mapped_file_win.cc b/base/files/memory_mapped_file_win.cc
index 9943773bec40..777b32358f86 100644
--- a/base/files/memory_mapped_file_win.cc
+++ b/base/files/memory_mapped_file_win.cc
@@ -149,4 +149,26 @@ void MemoryMappedFile::CloseHandles() {
length_ = 0;
}
+#if defined(MOZ_ZUCCHINI)
+bool MemoryMappedFile::Flush() {
+ if (!data_) {
+ return false;
+ }
+
+ // Flush the memory-mapped view to disk.
+ if (!::FlushViewOfFile(data_, length_)) {
+ PLOG(ERROR) << "FlushViewOfFile failed";
+ return false;
+ }
+
+ // Flush the file buffers to ensure data is written to disk.
+ if (file_.IsValid() && !::FlushFileBuffers(file_.GetPlatformFile())) {
+ PLOG(ERROR) << "FlushFileBuffers failed";
+ return false;
+ }
+
+ return true;
+}
+#endif // MOZ_ZUCCHINI
+
} // namespace base
diff --git a/components/zucchini/mapped_file.cc b/components/zucchini/mapped_file.cc
index 8dfb9181fb90..0e786aabf15f 100644
--- a/components/zucchini/mapped_file.cc
+++ b/components/zucchini/mapped_file.cc
@@ -78,4 +78,14 @@ bool MappedFileWriter::Keep() {
return true;
}
+#if defined(MOZ_ZUCCHINI)
+bool MappedFileWriter::Flush() {
+ bool success = buffer_.Flush();
+ if (!success) {
+ error_ = "Failed to flush changes to disk.";
+ }
+ return success;
+}
+#endif // MOZ_ZUCCHINI
+
} // namespace zucchini
diff --git a/components/zucchini/mapped_file.h b/components/zucchini/mapped_file.h
index e8230e394dde..ed7d0f97217b 100644
--- a/components/zucchini/mapped_file.h
+++ b/components/zucchini/mapped_file.h
@@ -74,6 +74,12 @@ class MappedFileWriter {
// iff the operation succeeds.
bool Keep();
+#if defined(MOZ_ZUCCHINI)
+ // Flushes memory-mapped changes to disk. Returns true on success, false on
+ // error. On error, sets error_ so HasError() will return true.
+ bool Flush();
+#endif // MOZ_ZUCCHINI
+
private:
enum OnCloseDeleteBehavior {
kKeep,
--
2.49.0.windows.1