FAILED: patch "[PATCH] s390/bpf: Fix backward jumps" failed to apply to 4.0-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.0-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From b035b60ded132592055c0f9bd1cc280259c7de4b Mon Sep 17 00:00:00 2001
From: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Date: Thu, 21 May 2015 15:39:31 +0200
Subject: [PATCH] s390/bpf: Fix backward jumps

Currently all backward jumps crash for JITed s390x eBPF programs
with an illegal instruction program check and kernel panic. Because
for negative values the opcode of the jump instruction is overriden
by the negative branch offset an illegal instruction is generated
by the JIT:

 000003ff802da378: c01100000002   lgfi    %r1,2
 000003ff802da37e: fffffff52065   unknown <-- illegal instruction
 000003ff802da384: b904002e       lgr     %r2,%r14

So fix this and mask the offset in order not to damage the opcode.

Cc: stable@vger.kernel.org # 4.0+
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index d3766dd67e23..fee782acc2ee 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -250,7 +250,7 @@ static inline void reg_set_seen(struct bpf_jit *jit, u32 b1)
 ({								\
 	/* Branch instruction needs 6 bytes */			\
 	int rel = (addrs[i + off + 1] - (addrs[i + 1] - 6)) / 2;\
-	_EMIT6(op1 | reg(b1, b2) << 16 | rel, op2 | mask);	\
+	_EMIT6(op1 | reg(b1, b2) << 16 | (rel & 0xffff), op2 | mask);	\
 	REG_SET_SEEN(b1);					\
 	REG_SET_SEEN(b2);					\
 })