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XOR encoded next_object

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This commit adds a simple XOR encoding to the next_object pointer in
FreeObjects.  This removes the trivial way of getting hold of a physical
address from the system by observing the free list pointers in
deallocated objects.
This commit is contained in:
Matthew Parkinson
2021-07-26 09:56:48 +01:00
committed by Matthew Parkinson
parent b69505fc5d
commit 81bf341732
9 changed files with 136 additions and 65 deletions
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10
src/mem/remoteallocator.h
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@@ -27,7 +27,7 @@ namespace snmalloc
/**
* Global key for all remote lists.
*/
inline static FreeListKey key_global(0xdeadbeef);
inline static FreeListKey key_global(0xdeadbeef, 0xdeadbeef);
struct alignas(REMOTE_MIN_ALIGN) RemoteAllocator
{
@@ -50,7 +50,7 @@ namespace snmalloc
void init(CapPtr<FreeObject, CBAlloc> stub)
{
stub->atomic_store_null();
stub->atomic_store_null(key_global);
front = stub;
back.store(stub, std::memory_order_relaxed);
invariant();
@@ -74,12 +74,12 @@ namespace snmalloc
void enqueue(
CapPtr<FreeObject, CBAlloc> first,
CapPtr<FreeObject, CBAlloc> last,
FreeListKey& key)
const FreeListKey& key)
{
// Pushes a list of messages to the queue. Each message from first to
// last should be linked together through their next pointers.
invariant();
last->atomic_store_null();
last->atomic_store_null(key);
// exchange needs to be a release, so nullptr in next is visible.
CapPtr<FreeObject, CBAlloc> prev =
@@ -93,7 +93,7 @@ namespace snmalloc
return front;
}
std::pair<CapPtr<FreeObject, CBAlloc>, bool> dequeue(FreeListKey& key)
std::pair<CapPtr<FreeObject, CBAlloc>, bool> dequeue(const FreeListKey& key)
{
// Returns the front message, or null if not possible to return a message.
invariant();