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* [PATCH] bpf: fix possible spectre-v1 in find_and_alloc_map()
@ 2018-05-03 16:04 Mark Rutland
  2018-05-03 16:48 ` David Miller
  2018-05-04  0:16 ` Daniel Borkmann
  0 siblings, 2 replies; 4+ messages in thread
From: Mark Rutland @ 2018-05-03 16:04 UTC (permalink / raw)
  To: linux-kernel
  Cc: Mark Rutland, Alexei Starovoitov, Dan Carpenter, Daniel Borkmann,
	Peter Zijlstra, netdev

It's possible for userspace to control attr->map_type. Sanitize it when
using it as an array index to prevent an out-of-bounds value being used
under speculation.

Found by smatch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: netdev@vger.kernel.org
---
 kernel/bpf/syscall.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

I found this when running smatch over a v4.17-rc2 arm64 allyesconfig kernel.

IIUC this may allow for a speculative branch to an arbitrary gadget when we
subsequently call ops->map_alloc_check(attr).

Mark.

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 4ca46df19c9a..8a7acd0dbeb6 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -26,6 +26,7 @@
 #include <linux/cred.h>
 #include <linux/timekeeping.h>
 #include <linux/ctype.h>
+#include <linux/nospec.h>
 
 #define IS_FD_ARRAY(map) ((map)->map_type == BPF_MAP_TYPE_PROG_ARRAY || \
 			   (map)->map_type == BPF_MAP_TYPE_PERF_EVENT_ARRAY || \
@@ -102,12 +103,14 @@ const struct bpf_map_ops bpf_map_offload_ops = {
 static struct bpf_map *find_and_alloc_map(union bpf_attr *attr)
 {
 	const struct bpf_map_ops *ops;
+	u32 type = attr->map_type;
 	struct bpf_map *map;
 	int err;
 
-	if (attr->map_type >= ARRAY_SIZE(bpf_map_types))
+	if (type >= ARRAY_SIZE(bpf_map_types))
 		return ERR_PTR(-EINVAL);
-	ops = bpf_map_types[attr->map_type];
+	type = array_index_nospec(type, ARRAY_SIZE(bpf_map_types));
+	ops = bpf_map_types[type];
 	if (!ops)
 		return ERR_PTR(-EINVAL);
 
@@ -122,7 +125,7 @@ static struct bpf_map *find_and_alloc_map(union bpf_attr *attr)
 	if (IS_ERR(map))
 		return map;
 	map->ops = ops;
-	map->map_type = attr->map_type;
+	map->map_type = type;
 	return map;
 }
 
-- 
2.11.0

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH] bpf: fix possible spectre-v1 in find_and_alloc_map()
  2018-05-03 16:04 [PATCH] bpf: fix possible spectre-v1 in find_and_alloc_map() Mark Rutland
@ 2018-05-03 16:48 ` David Miller
  2018-05-04  0:16 ` Daniel Borkmann
  1 sibling, 0 replies; 4+ messages in thread
From: David Miller @ 2018-05-03 16:48 UTC (permalink / raw)
  To: mark.rutland; +Cc: linux-kernel, ast, dan.carpenter, daniel, peterz, netdev

From: Mark Rutland <mark.rutland@arm.com>
Date: Thu,  3 May 2018 17:04:59 +0100

> It's possible for userspace to control attr->map_type. Sanitize it when
> using it as an array index to prevent an out-of-bounds value being used
> under speculation.
> 
> Found by smatch.
> 
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>

Acked-by: David S. Miller <davem@davemloft.net>

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH] bpf: fix possible spectre-v1 in find_and_alloc_map()
  2018-05-03 16:04 [PATCH] bpf: fix possible spectre-v1 in find_and_alloc_map() Mark Rutland
  2018-05-03 16:48 ` David Miller
@ 2018-05-04  0:16 ` Daniel Borkmann
  2018-05-04 10:49   ` Mark Rutland
  1 sibling, 1 reply; 4+ messages in thread
From: Daniel Borkmann @ 2018-05-04  0:16 UTC (permalink / raw)
  To: Mark Rutland, linux-kernel
  Cc: Alexei Starovoitov, Dan Carpenter, Peter Zijlstra, netdev

On 05/03/2018 06:04 PM, Mark Rutland wrote:
> It's possible for userspace to control attr->map_type. Sanitize it when
> using it as an array index to prevent an out-of-bounds value being used
> under speculation.
> 
> Found by smatch.
> 
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: Dan Carpenter <dan.carpenter@oracle.com>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: netdev@vger.kernel.org

Applied to bpf tree, thanks Mark! I've also just submitted one for
BPF progs (http://patchwork.ozlabs.org/patch/908385/) which is same
situation.

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH] bpf: fix possible spectre-v1 in find_and_alloc_map()
  2018-05-04  0:16 ` Daniel Borkmann
@ 2018-05-04 10:49   ` Mark Rutland
  0 siblings, 0 replies; 4+ messages in thread
From: Mark Rutland @ 2018-05-04 10:49 UTC (permalink / raw)
  To: Daniel Borkmann
  Cc: linux-kernel, Alexei Starovoitov, Dan Carpenter, Peter Zijlstra, netdev

On Fri, May 04, 2018 at 02:16:31AM +0200, Daniel Borkmann wrote:
> On 05/03/2018 06:04 PM, Mark Rutland wrote:
> > It's possible for userspace to control attr->map_type. Sanitize it when
> > using it as an array index to prevent an out-of-bounds value being used
> > under speculation.
> > 
> > Found by smatch.
> > 
> > Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> > Cc: Alexei Starovoitov <ast@kernel.org>
> > Cc: Dan Carpenter <dan.carpenter@oracle.com>
> > Cc: Daniel Borkmann <daniel@iogearbox.net>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: netdev@vger.kernel.org
> 
> Applied to bpf tree, thanks Mark!

Cheers!

> I've also just submitted one for BPF progs
> (http://patchwork.ozlabs.org/patch/908385/) which is same situation.

That looks good to me. That case doesn't show up in my smatch results so
far, but I might just need a few more build iterations.

Thanks,
Mark.

^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2018-05-04 10:49 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2018-05-03 16:04 [PATCH] bpf: fix possible spectre-v1 in find_and_alloc_map() Mark Rutland
2018-05-03 16:48 ` David Miller
2018-05-04  0:16 ` Daniel Borkmann
2018-05-04 10:49   ` Mark Rutland

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