--- /dev/null
+From d4c5efdb97773f59a2b711754ca0953f24516739 Mon Sep 17 00:00:00 2001
+From: Daniel Borkmann <dborkman@redhat.com>
+Date: Tue, 26 Aug 2014 23:16:35 -0400
+Subject: random: add and use memzero_explicit() for clearing data
+
+From: Daniel Borkmann <dborkman@redhat.com>
+
+commit d4c5efdb97773f59a2b711754ca0953f24516739 upstream.
+
+zatimend has reported that in his environment (3.16/gcc4.8.3/corei7)
+memset() calls which clear out sensitive data in extract_{buf,entropy,
+entropy_user}() in random driver are being optimized away by gcc.
+
+Add a helper memzero_explicit() (similarly as explicit_bzero() variants)
+that can be used in such cases where a variable with sensitive data is
+being cleared out in the end. Other use cases might also be in crypto
+code. [ I have put this into lib/string.c though, as it's always built-in
+and doesn't need any dependencies then. ]
+
+Fixes kernel bugzilla: 82041
+
+Reported-by: zatimend@hotmail.co.uk
+Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
+Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
+Cc: Alexey Dobriyan <adobriyan@gmail.com>
+Signed-off-by: Theodore Ts'o <tytso@mit.edu>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ drivers/char/random.c | 10 +++++-----
+ include/linux/string.h | 5 +++--
+ lib/string.c | 16 ++++++++++++++++
+ 3 files changed, 24 insertions(+), 7 deletions(-)
+
+--- a/drivers/char/random.c
++++ b/drivers/char/random.c
+@@ -1063,8 +1063,8 @@ static void extract_buf(struct entropy_s
+ * pool while mixing, and hash one final time.
+ */
+ sha_transform(hash.w, extract, workspace);
+- memset(extract, 0, sizeof(extract));
+- memset(workspace, 0, sizeof(workspace));
++ memzero_explicit(extract, sizeof(extract));
++ memzero_explicit(workspace, sizeof(workspace));
+
+ /*
+ * In case the hash function has some recognizable output
+@@ -1076,7 +1076,7 @@ static void extract_buf(struct entropy_s
+ hash.w[2] ^= rol32(hash.w[2], 16);
+
+ memcpy(out, &hash, EXTRACT_SIZE);
+- memset(&hash, 0, sizeof(hash));
++ memzero_explicit(&hash, sizeof(hash));
+ }
+
+ static ssize_t extract_entropy(struct entropy_store *r, void *buf,
+@@ -1124,7 +1124,7 @@ static ssize_t extract_entropy(struct en
+ }
+
+ /* Wipe data just returned from memory */
+- memset(tmp, 0, sizeof(tmp));
++ memzero_explicit(tmp, sizeof(tmp));
+
+ return ret;
+ }
+@@ -1162,7 +1162,7 @@ static ssize_t extract_entropy_user(stru
+ }
+
+ /* Wipe data just returned from memory */
+- memset(tmp, 0, sizeof(tmp));
++ memzero_explicit(tmp, sizeof(tmp));
+
+ return ret;
+ }
+--- a/include/linux/string.h
++++ b/include/linux/string.h
+@@ -129,7 +129,7 @@ int bprintf(u32 *bin_buf, size_t size, c
+ #endif
+
+ extern ssize_t memory_read_from_buffer(void *to, size_t count, loff_t *ppos,
+- const void *from, size_t available);
++ const void *from, size_t available);
+
+ /**
+ * strstarts - does @str start with @prefix?
+@@ -141,7 +141,8 @@ static inline bool strstarts(const char
+ return strncmp(str, prefix, strlen(prefix)) == 0;
+ }
+
+-extern size_t memweight(const void *ptr, size_t bytes);
++size_t memweight(const void *ptr, size_t bytes);
++void memzero_explicit(void *s, size_t count);
+
+ /**
+ * kbasename - return the last part of a pathname.
+--- a/lib/string.c
++++ b/lib/string.c
+@@ -586,6 +586,22 @@ void *memset(void *s, int c, size_t coun
+ EXPORT_SYMBOL(memset);
+ #endif
+
++/**
++ * memzero_explicit - Fill a region of memory (e.g. sensitive
++ * keying data) with 0s.
++ * @s: Pointer to the start of the area.
++ * @count: The size of the area.
++ *
++ * memzero_explicit() doesn't need an arch-specific version as
++ * it just invokes the one of memset() implicitly.
++ */
++void memzero_explicit(void *s, size_t count)
++{
++ memset(s, 0, count);
++ OPTIMIZER_HIDE_VAR(s);
++}
++EXPORT_SYMBOL(memzero_explicit);
++
+ #ifndef __HAVE_ARCH_MEMCPY
+ /**
+ * memcpy - Copy one area of memory to another