From: Daniel Borkmann <dborkman@xxxxxxxxxx>
3.4.106-rc1 review patch. If anyone has any objections, please let me know.
------------------
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@xxxxxxxxxxxxx
Signed-off-by: Daniel Borkmann <dborkman@xxxxxxxxxx>
Acked-by: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>
Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
[lizf: Backported to 3.4:
- adjust context
- another memset() in extract_buf() needs to be converted]
Signed-off-by: Zefan Li <lizefan@xxxxxxxxxx>
---
drivers/char/random.c | 10 +++++-----
include/linux/string.h | 4 +++-
lib/string.c | 16 ++++++++++++++++
3 files changed, 24 insertions(+), 6 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 1052fc4..85172fa 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -932,8 +932,8 @@ static void extract_buf(struct entropy_store *r, __u8 *out)
* 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
@@ -956,7 +956,7 @@ static void extract_buf(struct entropy_store *r, __u8 *out)
}
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,
@@ -989,7 +989,7 @@ static ssize_t extract_entropy(struct entropy_store *r, void *buf,
}
/* Wipe data just returned from memory */
- memset(tmp, 0, sizeof(tmp));
+ memzero_explicit(tmp, sizeof(tmp));
return ret;
}
@@ -1027,7 +1027,7 @@ static ssize_t extract_entropy_user(struct entropy_store *r, void __user *buf,
}
/* Wipe data just returned from memory */
- memset(tmp, 0, sizeof(tmp));
+ memzero_explicit(tmp, sizeof(tmp));
return ret;
}
diff --git a/include/linux/string.h b/include/linux/string.h
index e033564..3d9feb7 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -133,7 +133,7 @@ int bprintf(u32 *bin_buf, size_t size, const char *fmt, ...) __printf(3, 4);
#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?
@@ -144,5 +144,7 @@ static inline bool strstarts(const char *str, const char *prefix)
{
return strncmp(str, prefix, strlen(prefix)) == 0;
}
+
+void memzero_explicit(void *s, size_t count);
#endif
#endif /* _LINUX_STRING_H_ */
diff --git a/lib/string.c b/lib/string.c
index e5878de..43d0781 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -586,6 +586,22 @@ void *memset(void *s, int c, size_t count)
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
--
1.9.1
--
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