From 45a29b37173ab724d8b90af7e0b1a9fda3acbeb2 Mon Sep 17 00:00:00 2001
From: Benjamin Barenblat <bbaren@google.com>
Date: Sat, 27 Jan 2018 17:05:58 -0500
Subject: Data.Digest: Switch back to EVP

Use the finalizer techniques demonstrated in
4e56c79b907da4a4654e5278bdcf94b08480a426 to safely allocate `EVP_MD_CTX`
on the Haskell heap. This allows us to return to the high-level EVP API,
eliminating much boilerplate code.
---
 src/Cleanse.hsc | 62 ---------------------------------------------------------
 1 file changed, 62 deletions(-)
 delete mode 100644 src/Cleanse.hsc

(limited to 'src/Cleanse.hsc')

diff --git a/src/Cleanse.hsc b/src/Cleanse.hsc
deleted file mode 100644
index bb60945..0000000
--- a/src/Cleanse.hsc
+++ /dev/null
@@ -1,62 +0,0 @@
-{-# LANGUAGE ScopedTypeVariables #-}
-
--- | This module wraps BoringSSL's @OPENSSL_cleanse@, which securely overwrites
--- memory. ("Securely" here means that BoringSSL uses some assembly magic to
--- prevent the compiler from optimizing out the write.) However, the module
--- doesn't actually expose @OPENSSL_cleanse@ directly; instead, it lets you
--- allocate 'ForeignPtr's with cleansing registered as a finalizer. GHC runs all
--- 'ForeignPtr' finalizers prior to program termination, which gives the
--- 'ForeignPtr's allocated this way the approximately same security guarantees
--- as memory allocated through BoringSSL's allocator interface. In particular,
--- unless you exit your program through GHC's foreign function interface, all
--- memory allocated through 'mallocCleansablePtr' will be forcibly cleared prior
--- to program exit.
-module Cleanse
-  ( mallocCleansablePtr
-  ) where
-
-import Foreign
-       (FinalizerPtr, ForeignPtr, Storable(poke, sizeOf),
-        addForeignPtrFinalizer, mallocForeignPtrBytes, withForeignPtr)
-import Foreign.C.Types
-import Foreign.ForeignPtr.Compat (plusForeignPtr)
-
-#include <stddef.h>
-
-#include <openssl/mem.h>
-
--- We implement 'mallocCleansablePtr' using the standard allocator technique of
--- saving the allocated region size immediately before the allocated region.
-
-#def struct __attribute__((__packed__)) Buffer {
-  size_t size;
-  char data[];
-};
-
-bufferSize :: Int
-bufferSize = #size struct Buffer
-
-dataOffset :: Int
-dataOffset = #offset struct Buffer, data
-
-mallocCleansablePtr :: forall a. Storable a => IO (ForeignPtr a)
-mallocCleansablePtr = do
-  -- Allocate the buffer.
-  let dataSize = sizeOf (undefined :: a)
-  fp <- mallocForeignPtrBytes (bufferSize + dataSize)
-  -- Save the data size.
-  withForeignPtr fp $ \p -> poke p (fromIntegral dataSize :: CSize)
-  -- Now that the size is saved, we can register the cleansing finalizer. This
-  -- will look at the size and wipe the buffer.
-  addForeignPtrFinalizer btlsCleansePtr fp
-  -- Return a pointer to the data region.
-  return (fp `plusForeignPtr` dataOffset :: ForeignPtr a)
-
--- The cleansing finalizer itself is totally straightforward.
-
-#def void btlsCleanse(struct Buffer* const p) {
-  OPENSSL_cleanse(p->data, p->size);
-}
-
-foreign import ccall "&btlsCleanse"
-  btlsCleansePtr :: FinalizerPtr a
-- 
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