FAILED: patch "[PATCH] s390/bpf: clear correct BPF accumulator register" failed to apply to 4.2-stable tree

FAILED: patch "[PATCH] s390/bpf: clear correct BPF accumulator register" failed to apply to 4.2-stable tree

[gregkh]

The patch below does not apply to the 4.2-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 f75298f5c3fee750ad170bb98556e366a45a4093 Mon Sep 17 00:00:00 2001
From: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Date: Wed, 29 Jul 2015 21:15:14 +0200
Subject: [PATCH] s390/bpf: clear correct BPF accumulator register

Currently we assumed the following BPF to eBPF register mapping:

 - BPF_REG_A -> BPF_REG_7
 - BPF_REG_X -> BPF_REG_8

Unfortunately this mapping is wrong. The correct mapping is:

 - BPF_REG_A -> BPF_REG_0
 - BPF_REG_X -> BPF_REG_7

So clear the correct registers and use the BPF_REG_A and BPF_REG_X
macros instead of BPF_REG_0/7.

Fixes: 054623105728 ("s390/bpf: Add s390x eBPF JIT compiler backend")
Cc: stable@vger.kernel.org # 4.0+
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 79c731e8d178..01ad16608f66 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -448,13 +448,13 @@ static void bpf_jit_prologue(struct bpf_jit *jit)
 		EMIT6_DISP_LH(0xe3000000, 0x0004, REG_SKB_DATA, REG_0,
 			      BPF_REG_1, offsetof(struct sk_buff, data));
 	}
-	/* BPF compatibility: clear A (%b7) and X (%b8) registers */
-	if (REG_SEEN(BPF_REG_7))
-		/* lghi %b7,0 */
-		EMIT4_IMM(0xa7090000, BPF_REG_7, 0);
-	if (REG_SEEN(BPF_REG_8))
-		/* lghi %b8,0 */
-		EMIT4_IMM(0xa7090000, BPF_REG_8, 0);
+	/* BPF compatibility: clear A (%b0) and X (%b7) registers */
+	if (REG_SEEN(BPF_REG_A))
+		/* lghi %ba,0 */
+		EMIT4_IMM(0xa7090000, BPF_REG_A, 0);
+	if (REG_SEEN(BPF_REG_X))
+		/* lghi %bx,0 */
+		EMIT4_IMM(0xa7090000, BPF_REG_X, 0);
 }
 
 /*