From 972ab6d437272edb268f2bf1a515027192b14b58 Mon Sep 17 00:00:00 2001
From: Moonchild <moonchild@palemoon.org>
Date: Mon, 3 Aug 2020 09:41:42 +0000
Subject: [js] Try to catch bad pointers for GC and bail if not valid.

---
 js/public/HeapAPI.h   | 37 +++++++++++++++++++++++++++++++++++++
 js/src/gc/Marking.cpp |  5 +++++
 2 files changed, 42 insertions(+)

diff --git a/js/public/HeapAPI.h b/js/public/HeapAPI.h
index fef6c0c78..d033d3706 100644
--- a/js/public/HeapAPI.h
+++ b/js/public/HeapAPI.h
@@ -51,6 +51,7 @@ const size_t ChunkMarkBitmapBits = 129024;
 const size_t ChunkRuntimeOffset = ChunkSize - sizeof(void*);
 const size_t ChunkTrailerSize = 2 * sizeof(uintptr_t) + sizeof(uint64_t);
 const size_t ChunkLocationOffset = ChunkSize - ChunkTrailerSize;
+const size_t ChunkStoreBufferOffset = ChunkSize - ChunkTrailerSize + sizeof(uint64_t);
 const size_t ArenaZoneOffset = sizeof(size_t);
 const size_t ArenaHeaderSize = sizeof(size_t) + 2 * sizeof(uintptr_t) +
                                sizeof(size_t) + sizeof(uintptr_t);
@@ -326,6 +327,20 @@ CellIsMarkedGray(const Cell* cell)
 extern JS_PUBLIC_API(bool)
 CellIsMarkedGrayIfKnown(const Cell* cell);
 
+MOZ_ALWAYS_INLINE ChunkLocation GetCellLocation(const void* cell) {
+  uintptr_t addr = uintptr_t(cell);
+  addr &= ~js::gc::ChunkMask;
+  addr |= js::gc::ChunkLocationOffset;
+  return *reinterpret_cast<ChunkLocation*>(addr);
+}
+
+MOZ_ALWAYS_INLINE bool NurseryCellHasStoreBuffer(const void* cell) {
+  uintptr_t addr = uintptr_t(cell);
+  addr &= ~js::gc::ChunkMask;
+  addr |= js::gc::ChunkStoreBufferOffset;
+  return *reinterpret_cast<void**>(addr) != nullptr;
+}
+
 } /* namespace detail */
 
 MOZ_ALWAYS_INLINE bool
@@ -341,6 +356,28 @@ IsInsideNursery(const js::gc::Cell* cell)
     return location == ChunkLocation::Nursery;
 }
 
+MOZ_ALWAYS_INLINE bool IsCellPointerValid(const void* cell) {
+  auto addr = uintptr_t(cell);
+  if (addr < ChunkSize || addr % CellSize != 0) {
+    return false;
+  }
+  auto location = detail::GetCellLocation(cell);
+  if (location == ChunkLocation::TenuredHeap) {
+    return !!detail::GetGCThingZone(addr);
+  }
+  if (location == ChunkLocation::Nursery) {
+    return detail::NurseryCellHasStoreBuffer(cell);
+  }
+  return false;
+}
+
+MOZ_ALWAYS_INLINE bool IsCellPointerValidOrNull(const void* cell) {
+  if (!cell) {
+    return true;
+  }
+  return IsCellPointerValid(cell);
+}
+
 } /* namespace gc */
 } /* namespace js */
 
diff --git a/js/src/gc/Marking.cpp b/js/src/gc/Marking.cpp
index 43e325394..b4db0297a 100644
--- a/js/src/gc/Marking.cpp
+++ b/js/src/gc/Marking.cpp
@@ -2267,6 +2267,8 @@ void
 js::gc::StoreBuffer::SlotsEdge::trace(TenuringTracer& mover) const
 {
     NativeObject* obj = object();
+    if(!IsCellPointerValid(obj))
+        return;
 
     // Beware JSObject::swap exchanging a native object for a non-native one.
     if (!obj->isNative())
@@ -2336,6 +2338,8 @@ js::gc::StoreBuffer::traceWholeCells(TenuringTracer& mover)
 {
     for (ArenaCellSet* cells = bufferWholeCell; cells; cells = cells->next) {
         Arena* arena = cells->arena;
+        if(!IsCellPointerValid(arena))
+            continue;
 
         MOZ_ASSERT(arena->bufferedCells == cells);
         arena->bufferedCells = &ArenaCellSet::Empty;
@@ -2364,6 +2368,7 @@ js::gc::StoreBuffer::CellPtrEdge::trace(TenuringTracer& mover) const
 {
     if (!*edge)
         return;
+    // XXX: We should check if the cell pointer is valid here too
 
     MOZ_ASSERT((*edge)->getTraceKind() == JS::TraceKind::Object);
     mover.traverse(reinterpret_cast<JSObject**>(edge));
-- 
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