Patch "s390/bpf: reduce maximum program size to 64 KB" has been added to the 4.6-stable tree

Patch "s390/bpf: reduce maximum program size to 64 KB" has been added to the 4.6-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    s390/bpf: reduce maximum program size to 64 KB

to the 4.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     s390-bpf-reduce-maximum-program-size-to-64-kb.patch
and it can be found in the queue-4.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 0fa963553a5c28d8f8aabd8878326d3f782045fc Mon Sep 17 00:00:00 2001
From: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Date: Thu, 12 May 2016 18:10:48 +0200
Subject: s390/bpf: reduce maximum program size to 64 KB

From: Michael Holzheu <holzheu@linux.vnet.ibm.com>

commit 0fa963553a5c28d8f8aabd8878326d3f782045fc upstream.

The s390 BFP compiler currently uses relative branch instructions
that only support jumps up to 64 KB. Examples are "j", "jnz", "cgrj",
etc.  Currently the maximum size of s390 BPF programs is set
to 0x7ffff.  If branches over 64 KB are generated the, kernel can
crash due to incorrect code.

So fix this an reduce the maximum size to 64 KB. Programs larger than
that will be interpreted.

Fixes: ce2b6ad9c185 ("s390/bpf: increase BPF_SIZE_MAX")
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/s390/net/bpf_jit_comp.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -45,7 +45,7 @@ struct bpf_jit {
 	int labels[1];		/* Labels for local jumps */
 };
 
-#define BPF_SIZE_MAX	0x7ffff	/* Max size for program (20 bit signed displ) */
+#define BPF_SIZE_MAX	0xffff	/* Max size for program (16 bit branches) */
 
 #define SEEN_SKB	1	/* skb access */
 #define SEEN_MEM	2	/* use mem[] for temporary storage */


Patches currently in stable-queue which might be from holzheu@linux.vnet.ibm.com are

queue-4.6/s390-bpf-fix-recache-skb-data-hlen-for-skb_vlan_push-pop.patch
queue-4.6/s390-bpf-reduce-maximum-program-size-to-64-kb.patch