[PATCH 2/2] malloc: implement free_sensitive()

[Sascha Hauer <s.hauer@pengutronix.de>]

barebox sometimes stores sensitive data in memory. Add a
(k)free_sensitive() function which zeroes out the memory before freeing it.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
 common/Makefile      |  1 +
 common/malloc.c      | 14 ++++++++++++++
 include/dma.h        |  5 +++++
 include/linux/slab.h |  5 +++++
 include/malloc.h     |  1 +
 5 files changed, 26 insertions(+)
 create mode 100644 common/malloc.c

diff --git a/common/Makefile b/common/Makefile
index 96498790b3..e88f60b6d7 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -52,6 +52,7 @@ obj-$(CONFIG_MALLOC_DLMALLOC)	+= dlmalloc.o
 obj-$(CONFIG_MALLOC_TLSF)	+= tlsf_malloc.o tlsf.o calloc.o
 KASAN_SANITIZE_tlsf.o := n
 obj-$(CONFIG_MALLOC_DUMMY)	+= dummy_malloc.o calloc.o
+obj-y				+= malloc.o
 obj-$(CONFIG_MEMINFO)		+= meminfo.o
 obj-$(CONFIG_MENU)		+= menu.o
 obj-$(CONFIG_MODULES)		+= module.o
diff --git a/common/malloc.c b/common/malloc.c
new file mode 100644
index 0000000000..9dbad98701
--- /dev/null
+++ b/common/malloc.c
@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <malloc.h>
+#include <string.h>
+
+void free_sensitive(void *mem)
+{
+	size_t size = malloc_usable_size(mem);
+
+	if (size)
+		memzero_explicit(mem, size);
+
+	free(mem);
+}
diff --git a/include/dma.h b/include/dma.h
index 4fcd114bb6..c2b1bee358 100644
--- a/include/dma.h
+++ b/include/dma.h
@@ -41,6 +41,11 @@ static inline void dma_free(void *mem)
 	free(mem);
 }
 
+static inline void dma_free_sensitive(void *mem)
+{
+	free_sensitive(mem);
+}
+
 #define DMA_BIT_MASK(n)	(((n) == 64) ? ~0ULL : ((1ULL<<(n))-1))
 
 #define DMA_MASK_NONE	0x0ULL
diff --git a/include/linux/slab.h b/include/linux/slab.h
index a63aad1c34..5e08c7697d 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -62,6 +62,11 @@ static inline void kfree(const void *mem)
 	dma_free((void *)mem);
 }
 
+static inline void kfree_sensitive(const void *objp)
+{
+	dma_free_sensitive((void *)objp);
+}
+
 static inline void *kmem_cache_alloc(struct kmem_cache *cache, gfp_t flags)
 {
 	void *mem = kmalloc(cache->size, flags);
diff --git a/include/malloc.h b/include/malloc.h
index 5cdff0a4f9..fc0c94855e 100644
--- a/include/malloc.h
+++ b/include/malloc.h
@@ -8,6 +8,7 @@
 void *malloc(size_t) __alloc_size(1);
 size_t malloc_usable_size(void *);
 void free(void *);
+void free_sensitive(void *);
 void *realloc(void *, size_t) __realloc_size(2);
 void *memalign(size_t, size_t) __alloc_size(2);
 void *calloc(size_t, size_t) __alloc_size(1, 2);
-- 
2.39.2