powerpc/bpf/jit: Fix 32-bit JIT for seccomp_data access

I am using SECCOMP to filter syscalls on a ppc32 platform, and noticed
that the JIT compiler was failing on the BPF even though the
interpreter was working fine.

The issue was that the compiler was missing one of the instructions
used by SECCOMP, so here is a patch to enable JIT for that
instruction.

Fixes: eb84bab0fb38 ("ppc: Kconfig: Enable BPF JIT on ppc32")
Signed-off-by: Mark Lord <mlord@pobox.com>
Acked-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/net/bpf_jit_comp.c

@@ -327,6 +327,9 @@ static int bpf_jit_build_body(struct bpf_prog *fp, u32 *image,
 			BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, len) != 4);
 			PPC_LWZ_OFFS(r_A, r_skb, offsetof(struct sk_buff, len));
 			break;
+		case BPF_LDX | BPF_W | BPF_ABS: /* A = *((u32 *)(seccomp_data + K)); */
+			PPC_LWZ_OFFS(r_A, r_skb, K);
+			break;
 		case BPF_LDX | BPF_W | BPF_LEN: /* X = skb->len; */
 			PPC_LWZ_OFFS(r_X, r_skb, offsetof(struct sk_buff, len));
 			break;