* [PATCH] random: add and use memzero_explicit() for clearing data
@ 2014-08-25 20:01 Daniel Borkmann
2014-08-25 20:35 ` Alexey Dobriyan
` (2 more replies)
0 siblings, 3 replies; 11+ messages in thread
From: Daniel Borkmann @ 2014-08-25 20:01 UTC (permalink / raw)
To: tytso; +Cc: zatimend, linux-kernel, Hannes Frederic Sowa, Alexey Dobriyan
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>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
---
drivers/char/random.c | 8 ++++----
include/linux/string.h | 5 +++--
lib/string.c | 16 ++++++++++++++++
3 files changed, 23 insertions(+), 6 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c
index c18d41d..8c86a95 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1106,7 +1106,7 @@ static void extract_buf(struct entropy_store *r, __u8 *out)
__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_store *r, __u8 *out)
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 entropy_store *r, void *buf,
}
/* 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(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 d36977e..3b42b37 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -132,7 +132,7 @@ 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?
@@ -144,7 +144,8 @@ static inline bool strstarts(const char *str, const char *prefix)
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.
diff --git a/lib/string.c b/lib/string.c
index 992bf30..0f3a927 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -604,6 +604,22 @@ 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
--
1.7.11.7
^ permalink raw reply related [flat|nested] 11+ messages in thread
* Re: [PATCH] random: add and use memzero_explicit() for clearing data
2014-08-25 20:01 [PATCH] random: add and use memzero_explicit() for clearing data Daniel Borkmann
@ 2014-08-25 20:35 ` Alexey Dobriyan
2014-08-25 20:38 ` Daniel Borkmann
2014-08-25 23:11 ` Hannes Frederic Sowa
2014-12-01 10:27 ` Dan Carpenter
2 siblings, 1 reply; 11+ messages in thread
From: Alexey Dobriyan @ 2014-08-25 20:35 UTC (permalink / raw)
To: Daniel Borkmann; +Cc: tytso, zatimend, linux-kernel, Hannes Frederic Sowa
On Mon, Aug 25, 2014 at 10:01:39PM +0200, Daniel Borkmann wrote:
> +void memzero_explicit(void *s, size_t count)
> +{
> + memset(s, 0, count);
> + OPTIMIZER_HIDE_VAR(s);
> +}
BSD seems to name it explicit_bzero().
Alexey
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH] random: add and use memzero_explicit() for clearing data
2014-08-25 20:35 ` Alexey Dobriyan
@ 2014-08-25 20:38 ` Daniel Borkmann
0 siblings, 0 replies; 11+ messages in thread
From: Daniel Borkmann @ 2014-08-25 20:38 UTC (permalink / raw)
To: Alexey Dobriyan; +Cc: tytso, zatimend, linux-kernel, Hannes Frederic Sowa
On 08/25/2014 10:35 PM, Alexey Dobriyan wrote:
> On Mon, Aug 25, 2014 at 10:01:39PM +0200, Daniel Borkmann wrote:
>> +void memzero_explicit(void *s, size_t count)
>> +{
>> + memset(s, 0, count);
>> + OPTIMIZER_HIDE_VAR(s);
>> +}
>
> BSD seems to name it explicit_bzero().
Sure, that's what I wrote in the commit log. But we don't have
bzero(), and I think the name is more clear and conform to
mem*() API.
Best,
Daniel
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH] random: add and use memzero_explicit() for clearing data
2014-08-25 20:01 [PATCH] random: add and use memzero_explicit() for clearing data Daniel Borkmann
2014-08-25 20:35 ` Alexey Dobriyan
@ 2014-08-25 23:11 ` Hannes Frederic Sowa
2014-08-27 3:21 ` Theodore Ts'o
2014-12-01 10:27 ` Dan Carpenter
2 siblings, 1 reply; 11+ messages in thread
From: Hannes Frederic Sowa @ 2014-08-25 23:11 UTC (permalink / raw)
To: Daniel Borkmann; +Cc: tytso, zatimend, linux-kernel, Alexey Dobriyan
On Mo, 2014-08-25 at 22:01 +0200, Daniel Borkmann wrote:
> 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>
> Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
> Cc: Alexey Dobriyan <adobriyan@gmail.com>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
In case this pattern of important function calls getting optimized away
emerges more often we could also go with a wrapper which forces the
execution of the function, like:
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -181,6 +181,13 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
#define OPTIMIZER_HIDE_VAR(var) barrier()
#endif
+#ifndef OPTIMIZER_FORCE_CALL
+#define OPTIMIZER_FORCE_CALL(func, args...) ({ \
+ typeof(func) * volatile __func = (func); \
+ __func(args); \
+ })
+#endif
+
/* Not-quite-unique ID. */
#ifndef __UNIQUE_ID
# define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __LINE__)
Thanks,
Hannes
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH] random: add and use memzero_explicit() for clearing data
2014-08-25 23:11 ` Hannes Frederic Sowa
@ 2014-08-27 3:21 ` Theodore Ts'o
0 siblings, 0 replies; 11+ messages in thread
From: Theodore Ts'o @ 2014-08-27 3:21 UTC (permalink / raw)
To: Hannes Frederic Sowa
Cc: Daniel Borkmann, zatimend, linux-kernel, Alexey Dobriyan
On Tue, Aug 26, 2014 at 01:11:30AM +0200, Hannes Frederic Sowa wrote:
> On Mo, 2014-08-25 at 22:01 +0200, Daniel Borkmann wrote:
> > 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>
> > Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
> > Cc: Alexey Dobriyan <adobriyan@gmail.com>
>
> Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Applied to the random tree, thanks.
- Ted
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH] random: add and use memzero_explicit() for clearing data
2014-08-25 20:01 [PATCH] random: add and use memzero_explicit() for clearing data Daniel Borkmann
2014-08-25 20:35 ` Alexey Dobriyan
2014-08-25 23:11 ` Hannes Frederic Sowa
@ 2014-12-01 10:27 ` Dan Carpenter
2014-12-01 11:04 ` Daniel Borkmann
2 siblings, 1 reply; 11+ messages in thread
From: Dan Carpenter @ 2014-12-01 10:27 UTC (permalink / raw)
To: Daniel Borkmann
Cc: tytso, zatimend, linux-kernel, Hannes Frederic Sowa,
Alexey Dobriyan, Kees Cook, Julia Lawall
On Mon, Aug 25, 2014 at 10:01:39PM +0200, Daniel Borkmann wrote:
> 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
>
What???
That's not ok. We totally rely on memset to work. Every single memset
that I have added was absolutely necessary. This should be fixed
so that memset works instead of adding a work around for specific
drivers.
regards,
dan carpnter
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH] random: add and use memzero_explicit() for clearing data
2014-12-01 10:27 ` Dan Carpenter
@ 2014-12-01 11:04 ` Daniel Borkmann
2014-12-01 11:29 ` Dan Carpenter
0 siblings, 1 reply; 11+ messages in thread
From: Daniel Borkmann @ 2014-12-01 11:04 UTC (permalink / raw)
To: Dan Carpenter
Cc: tytso, zatimend, linux-kernel, Hannes Frederic Sowa,
Alexey Dobriyan, Kees Cook, Julia Lawall
On 12/01/2014 11:27 AM, Dan Carpenter wrote:
> On Mon, Aug 25, 2014 at 10:01:39PM +0200, Daniel Borkmann wrote:
>> 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
>
> What???
>
> That's not ok. We totally rely on memset to work. Every single memset
> that I have added was absolutely necessary. This should be fixed
> so that memset works instead of adding a work around for specific
> drivers.
Well, BSD has helpers such as bzero_explicit() for such cases to work
around this, which memzero_explicit() similarly does; see also [1].
[1] https://gcc.gnu.org/ml/gcc-help/2014-10/msg00059.html
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH] random: add and use memzero_explicit() for clearing data
2014-12-01 11:04 ` Daniel Borkmann
@ 2014-12-01 11:29 ` Dan Carpenter
2014-12-01 11:38 ` Dan Carpenter
2014-12-01 11:48 ` Daniel Borkmann
0 siblings, 2 replies; 11+ messages in thread
From: Dan Carpenter @ 2014-12-01 11:29 UTC (permalink / raw)
To: Daniel Borkmann
Cc: tytso, zatimend, linux-kernel, Hannes Frederic Sowa,
Alexey Dobriyan, Kees Cook, Julia Lawall
On Mon, Dec 01, 2014 at 12:04:57PM +0100, Daniel Borkmann wrote:
> Well, BSD has helpers such as bzero_explicit() for such cases to work
> around this, which memzero_explicit() similarly does; see also [1].
>
> [1] https://gcc.gnu.org/ml/gcc-help/2014-10/msg00059.html
We should make memset() a define and call a custom function internally.
Otherwise there are thousands of calls to memset() which we would need
to audit. We could do some of this automatically but it's going to be a
mess.
regards,
dan carpenter
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH] random: add and use memzero_explicit() for clearing data
2014-12-01 11:29 ` Dan Carpenter
@ 2014-12-01 11:38 ` Dan Carpenter
2014-12-01 13:39 ` Daniel Borkmann
2014-12-01 11:48 ` Daniel Borkmann
1 sibling, 1 reply; 11+ messages in thread
From: Dan Carpenter @ 2014-12-01 11:38 UTC (permalink / raw)
To: Daniel Borkmann
Cc: tytso, zatimend, linux-kernel, Hannes Frederic Sowa,
Alexey Dobriyan, Kees Cook, Julia Lawall
On Mon, Dec 01, 2014 at 02:29:57PM +0300, Dan Carpenter wrote:
> On Mon, Dec 01, 2014 at 12:04:57PM +0100, Daniel Borkmann wrote:
> > Well, BSD has helpers such as bzero_explicit() for such cases to work
> > around this, which memzero_explicit() similarly does; see also [1].
> >
> > [1] https://gcc.gnu.org/ml/gcc-help/2014-10/msg00059.html
>
> We should make memset() a define and call a custom function internally.
>
Or we could specify -fno-builtin-memset like the GCC people suggest.
regards,
dan carpenter
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH] random: add and use memzero_explicit() for clearing data
2014-12-01 11:29 ` Dan Carpenter
2014-12-01 11:38 ` Dan Carpenter
@ 2014-12-01 11:48 ` Daniel Borkmann
1 sibling, 0 replies; 11+ messages in thread
From: Daniel Borkmann @ 2014-12-01 11:48 UTC (permalink / raw)
To: Dan Carpenter
Cc: tytso, zatimend, linux-kernel, Hannes Frederic Sowa,
Alexey Dobriyan, Kees Cook, Julia Lawall
On 12/01/2014 12:29 PM, Dan Carpenter wrote:
> On Mon, Dec 01, 2014 at 12:04:57PM +0100, Daniel Borkmann wrote:
>> Well, BSD has helpers such as bzero_explicit() for such cases to work
>> around this, which memzero_explicit() similarly does; see also [1].
>>
>> [1] https://gcc.gnu.org/ml/gcc-help/2014-10/msg00059.html
>
> We should make memset() a define and call a custom function internally.
>
> Otherwise there are thousands of calls to memset() which we would need
> to audit. We could do some of this automatically but it's going to be a
> mess.
Sort of, yeah; for now random driver and crypto subsystem, which I consider
the main candidates, have been converted and with Julia's latest patch set
from today (via coccinelle) also remaining arch-specific crypto drivers.
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH] random: add and use memzero_explicit() for clearing data
2014-12-01 11:38 ` Dan Carpenter
@ 2014-12-01 13:39 ` Daniel Borkmann
0 siblings, 0 replies; 11+ messages in thread
From: Daniel Borkmann @ 2014-12-01 13:39 UTC (permalink / raw)
To: Dan Carpenter
Cc: tytso, zatimend, linux-kernel, Hannes Frederic Sowa,
Alexey Dobriyan, Kees Cook, Julia Lawall
On 12/01/2014 12:38 PM, Dan Carpenter wrote:
> On Mon, Dec 01, 2014 at 02:29:57PM +0300, Dan Carpenter wrote:
>> On Mon, Dec 01, 2014 at 12:04:57PM +0100, Daniel Borkmann wrote:
>>> Well, BSD has helpers such as bzero_explicit() for such cases to work
>>> around this, which memzero_explicit() similarly does; see also [1].
>>>
>>> [1] https://gcc.gnu.org/ml/gcc-help/2014-10/msg00059.html
>>
>> We should make memset() a define and call a custom function internally.
>
> Or we could specify -fno-builtin-memset like the GCC people suggest.
If there's a better, reliable way, I'm all for it. To me, memzero_explicit()
seemed like the least intrusive variant doing the job, I'm unsure if globally
setting -fno-builtin-memset will come with unforeseen side-effects on some
archs (besides performance-wise).
^ permalink raw reply [flat|nested] 11+ messages in thread
end of thread, other threads:[~2014-12-01 13:40 UTC | newest]
Thread overview: 11+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2014-08-25 20:01 [PATCH] random: add and use memzero_explicit() for clearing data Daniel Borkmann
2014-08-25 20:35 ` Alexey Dobriyan
2014-08-25 20:38 ` Daniel Borkmann
2014-08-25 23:11 ` Hannes Frederic Sowa
2014-08-27 3:21 ` Theodore Ts'o
2014-12-01 10:27 ` Dan Carpenter
2014-12-01 11:04 ` Daniel Borkmann
2014-12-01 11:29 ` Dan Carpenter
2014-12-01 11:38 ` Dan Carpenter
2014-12-01 13:39 ` Daniel Borkmann
2014-12-01 11:48 ` Daniel Borkmann
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