| 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 | 8 ++++---- |
| include/linux/string.h | 5 +++-- |
| lib/string.c | 16 ++++++++++++++++ |
| 3 files changed, 23 insertions(+), 6 deletions(-) |
| |
| --- a/drivers/char/random.c |
| +++ b/drivers/char/random.c |
| @@ -1106,7 +1106,7 @@ static void extract_buf(struct entropy_s |
| __mix_pool_bytes(r, hash.w, sizeof(hash.w)); |
| spin_unlock_irqrestore(&r->lock, flags); |
| |
| - memset(workspace, 0, sizeof(workspace)); |
| + memzero_explicit(workspace, sizeof(workspace)); |
| |
| /* |
| * In case the hash function has some recognizable output |
| @@ -1118,7 +1118,7 @@ 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)); |
| } |
| |
| /* |
| @@ -1175,7 +1175,7 @@ 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; |
| } |
| @@ -1218,7 +1218,7 @@ 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 |
| @@ -132,7 +132,7 @@ 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? |
| @@ -144,7 +144,8 @@ 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 |
| @@ -604,6 +604,22 @@ 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 |