powerpc/bpf: Reject atomic ops in ppc32 JIT

Commit 91c960b ("bpf: Rename BPF_XADD and prepare to encode other
atomics in .imm") converted BPF_XADD to BPF_ATOMIC and updated all JIT
implementations to reject JIT'ing instructions with an immediate value
different from BPF_ADD. However, ppc32 BPF JIT was implemented around
the same time and didn't include the same change. Update the ppc32 JIT
accordingly.

Fixes: 51c66ad ("powerpc/bpf: Implement extended BPF on PPC32")
Cc: stable@vger.kernel.org # v5.13+
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/426699046d89fe50f66ecf74bd31c01eda976ba5.1625145429.git.naveen.n.rao@linux.vnet.ibm.com

arch/powerpc/net/bpf_jit_comp32.c

@@ -773,9 +773,17 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
 			break;
 
 		/*
-		 * BPF_STX XADD (atomic_add)
+		 * BPF_STX ATOMIC (atomic ops)
 		 */
-		case BPF_STX | BPF_XADD | BPF_W: /* *(u32 *)(dst + off) += src */
+		case BPF_STX | BPF_ATOMIC | BPF_W:
+			if (imm != BPF_ADD) {
+				pr_err_ratelimited("eBPF filter atomic op code %02x (@%d) unsupported\n",
+						   code, i);
+				return -ENOTSUPP;
+			}
+
+			/* *(u32 *)(dst + off) += src */
+
 			bpf_set_seen_register(ctx, tmp_reg);
 			/* Get offset into TMP_REG */
 			EMIT(PPC_RAW_LI(tmp_reg, off));
@@ -789,7 +797,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
 			PPC_BCC_SHORT(COND_NE, (ctx->idx - 3) * 4);
 			break;
 
-		case BPF_STX | BPF_XADD | BPF_DW: /* *(u64 *)(dst + off) += src */
+		case BPF_STX | BPF_ATOMIC | BPF_DW: /* *(u64 *)(dst + off) += src */
 			return -EOPNOTSUPP;
 
 		/*