s390/bpf,jit: fix address randomization

Add misssing braces to hole calculation. This resulted in an addition
instead of an substraction. Which in turn means that the jit compiler
could try to write out of bounds of the allocated piece of memory.

This bug was introduced with aa2d2c73 "s390/bpf,jit: address randomize
and write protect jit code".

Fixes this one:

[   37.320956] Unable to handle kernel pointer dereference at virtual kernel address 000003ff80231000
[   37.320984] Oops: 0011 [#1] PREEMPT SMP DEBUG_PAGEALLOC
[   37.320993] Modules linked in: dm_multipath scsi_dh eadm_sch dm_mod ctcm fsm autofs4
[   37.321007] CPU: 28 PID: 6443 Comm: multipathd Not tainted 3.10.9-61.x.20130829-s390xdefault #1
[   37.321011] task: 0000004ada778000 ti: 0000004ae3304000 task.ti: 0000004ae3304000
[   37.321014] Krnl PSW : 0704c00180000000 000000000012d1de (bpf_jit_compile+0x198e/0x23d0)
[   37.321022]            R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:0 PM:0 EA:3
               Krnl GPRS: 000000004350207d 0000004a00000001 0000000000000007 000003ff80231002
[   37.321029]            0000000000000007 000003ff80230ffe 00000000a7740000 000003ff80230f76
[   37.321032]            000003ffffffffff 000003ff00000000 000003ff0000007d 000000000071e820
[   37.321035]            0000004adbe99950 000000000071ea18 0000004af3d9e7c0 0000004ae3307b80
[   37.321046] Krnl Code: 000000000012d1d0: 41305004            la      %r3,4(%r5)
                          000000000012d1d4: e330f0f80021        clg     %r3,248(%r15)
                         #000000000012d1da: a7240009            brc     2,12d1ec
                         >000000000012d1de: 50805000            st      %r8,0(%r5)
                          000000000012d1e2: e330f0f00004        lg      %r3,240(%r15)
                          000000000012d1e8: 41303004            la      %r3,4(%r3)
                          000000000012d1ec: e380f0e00004        lg      %r8,224(%r15)
                          000000000012d1f2: e330f0f00024        stg     %r3,240(%r15)
[   37.321074] Call Trace:
[   37.321077] ([<000000000012da78>] bpf_jit_compile+0x2228/0x23d0)
[   37.321083]  [<00000000006007c2>] sk_attach_filter+0xfe/0x214
[   37.321090]  [<00000000005d2d92>] sock_setsockopt+0x926/0xbdc
[   37.321097]  [<00000000005cbfb6>] SyS_setsockopt+0x8a/0xe8
[   37.321101]  [<00000000005ccaa8>] SyS_socketcall+0x264/0x364
[   37.321106]  [<0000000000713f1c>] sysc_nr_ok+0x22/0x28
[   37.321113]  [<000003fffce10ea8>] 0x3fffce10ea8
[   37.321118] INFO: lockdep is turned off.
[   37.321121] Last Breaking-Event-Address:
[   37.321124]  [<000000000012d192>] bpf_jit_compile+0x1942/0x23d0
[   37.321132]
[   37.321135] Kernel panic - not syncing: Fatal exception: panic_on_oops

Cc: stable@vger.kernel.org # v3.11
Signed-off-by: NHeiko Carstens <heiko.carstens@de.ibm.com>

arch/s390/net/bpf_jit_comp.c

@@ -805,7 +805,7 @@ static struct bpf_binary_header *bpf_alloc_binary(unsigned int bpfsize,
 		return NULL;
 	memset(header, 0, sz);
 	header->pages = sz / PAGE_SIZE;
-	hole = sz - bpfsize + sizeof(*header);
+	hole = sz - (bpfsize + sizeof(*header));
 	/* Insert random number of illegal instructions before BPF code
 	 * and make sure the first instruction starts at an even address.
 	 */