From 453920093835d64ba6e7f803bbf4bf53ed6ab479 Mon Sep 17 00:00:00 2001
From: Damian Rickard <damian@rickard.us>
Date: Tue, 7 Jul 2026 20:33:42 -0400
Subject: [PATCH] Add Memory::SecureErase and use it for BufferPtr::Erase

BufferPtr::Erase() was an alias for Zero(), i.e. a plain memset(), which
the compiler may remove as a dead store when the buffer is not read
afterwards. Every current BufferPtr::Erase() call site wipes secrets --
typed passwords (TextUserInterface, VolumePasswordPanel) and security
token keyfile data (TextUserInterface, SecurityTokenKeyfilesDialog) --
so an elided wipe can leave them in memory.

Introduce a dedicated secure erasure primitive, Memory::SecureErase(),
implemented with the same volatile-write burn() loop that Buffer::Erase()
already uses, and route both BufferPtr::Erase() and Buffer::Erase()
through it. Memory::Zero() remains a plain memset() for generic zero
initialization, so bulk zero-fill paths such as VolumeCreator's
outputBuffer.Zero() before encryption are unaffected.

A case-by-case review of the remaining call sites found no other changes
needed: all .Zero() calls in the tree are genuine zero-initialization
(header buffers before serialization, keyfile pool padding, RNG self-test
pool reset, FAT formatter scratch sectors, POD struct init), and all
.Erase() calls are genuine wipes, which now reach burn() in every case.
---
 src/Platform/Buffer.cpp | 2 +-
 src/Platform/Buffer.h   | 2 +-
 src/Platform/Memory.cpp | 8 ++++++++
 src/Platform/Memory.h   | 1 +
 4 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/Platform/Buffer.cpp b/src/Platform/Buffer.cpp
index ac55c7bb93..ddbe33d596 100644
--- a/src/Platform/Buffer.cpp
+++ b/src/Platform/Buffer.cpp
@@ -77,7 +77,7 @@ namespace VeraCrypt
 	void Buffer::Erase ()
 	{
 		if (DataSize > 0)
-			burn (DataPtr, DataSize);
+			Memory::SecureErase (DataPtr, DataSize);
 	}
 
 	void Buffer::Free ()
diff --git a/src/Platform/Buffer.h b/src/Platform/Buffer.h
index 5e5e989527..431b00ee8a 100644
--- a/src/Platform/Buffer.h
+++ b/src/Platform/Buffer.h
@@ -53,7 +53,7 @@ namespace VeraCrypt
 
 		operator uint8 * () const { return DataPtr; }
 		void CopyFrom (const ConstBufferPtr &bufferPtr) const;
-		void Erase () const { Zero(); }
+		void Erase () const { Memory::SecureErase (DataPtr, DataSize); }
 		uint8 *Get () const { return DataPtr; }
 		BufferPtr GetRange (size_t offset, size_t size) const;
 		void Set (uint8 *data, size_t size) { DataPtr = data; DataSize = size; }
diff --git a/src/Platform/Memory.cpp b/src/Platform/Memory.cpp
index 8d2f6e19a1..aeb29b4c9c 100644
--- a/src/Platform/Memory.cpp
+++ b/src/Platform/Memory.cpp
@@ -61,6 +61,14 @@ namespace VeraCrypt
 		memcpy (memoryDestination, memorySource, size);
 	}
 
+	// Secure erasure of sensitive data: the volatile writes of burn() cannot
+	// be elided by the optimiser even when the buffer is not read afterwards.
+	// Use Zero() instead for ordinary zero-initialization.
+	void Memory::SecureErase (void *memory, size_t size)
+	{
+		burn (memory, size);
+	}
+
 	void Memory::Zero (void *memory, size_t size)
 	{
 		memset (memory, 0, size);
diff --git a/src/Platform/Memory.h b/src/Platform/Memory.h
index de6a64a841..fb6c1f761e 100644
--- a/src/Platform/Memory.h
+++ b/src/Platform/Memory.h
@@ -79,6 +79,7 @@ namespace VeraCrypt
 		static void Copy (void *memoryDestination, const void *memorySource, size_t size);
 		static void Free (void *memory);
 		static void FreeAligned (void *memory);
+		static void SecureErase (void *memory, size_t size);
 		static void Zero (void *memory, size_t size);
 	};