[libc-commits] [libc] [libc] add option for hardened freelist (PR #205382)

[Daniel Thornburgh via libc-commits]

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@@ -80,35 +88,44 @@ template <size_t BUFF_SIZE> class FreeListHeapBuffer : public FreeListHeap {
   cpp::byte buffer[BUFF_SIZE];
 };
 
-LIBC_INLINE void FreeListHeap::init() {
+[[gnu::noinline]] LIBC_INLINE void
+FreeListHeap::init(const FreeListSecrets &secrets_arg) {
   LIBC_ASSERT(!is_initialized && "duplicate initialization");
+  secrets = secrets_arg;
   auto result = BlockRef::init(region());
   BlockRef block = *result;
   free_store.set_range({0, cpp::bit_ceil(block.inner_size())});
-  free_store.insert(block);
+  free_store.insert(block, secrets);
   is_initialized = true;
 }
 
 LIBC_INLINE void *FreeListHeap::allocate_impl(size_t alignment, size_t size) {
   if (size == 0)
     return nullptr;
 
-  if (!is_initialized)
+  if (!is_initialized) {
+#if LIBC_COPT_HARDEN_FREELIST
----------------
mysterymath wrote:

This seems onerous from a user point of view; all of this stuff is intended to be very internal. So, we'd need to invent something user-facing, which would invariably take the form of an embedding ABI. So, probably a C function like `__libc_malloc_init_secrets` that took 3 pointer args? I'd also wonder whether we could provide a reasonable default... not sure if there's a good cross-baremetal-device way to generate secrets, or an existing API we could call? Might be worth scanning around llvm for prior art here.

https://github.com/llvm/llvm-project/pull/205382