netdev - [PATCH bpf-next 11/13] bpf, mips64: remove unneeded zero check from div/mod with k

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Message-Id: <20180126223348.11250-12-daniel@iogearbox.net>
Date:   Fri, 26 Jan 2018 23:33:46 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     ast@...nel.org
Cc:     netdev@...r.kernel.org, Daniel Borkmann <daniel@...earbox.net>,
        David Daney <david.daney@...ium.com>
Subject: [PATCH bpf-next 11/13] bpf, mips64: remove unneeded zero check from div/mod with k

The verifier in both cBPF and eBPF reject div/mod by 0 imm,
so this can never load. Remove emitting such test and reject
it from being JITed instead (the latter is actually also not
needed, but given practice in sparc64, ppc64 today, so
doesn't hurt to add it here either).

Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Cc: David Daney <david.daney@...ium.com>
---
 arch/mips/net/ebpf_jit.c | 19 ++++---------------
 1 file changed, 4 insertions(+), 15 deletions(-)

diff --git a/arch/mips/net/ebpf_jit.c b/arch/mips/net/ebpf_jit.c
index 296f1410..3e2798b 100644
--- a/arch/mips/net/ebpf_jit.c
+++ b/arch/mips/net/ebpf_jit.c
@@ -741,16 +741,11 @@ static int build_one_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
 		break;
 	case BPF_ALU | BPF_DIV | BPF_K: /* ALU_IMM */
 	case BPF_ALU | BPF_MOD | BPF_K: /* ALU_IMM */
+		if (insn->imm == 0)
+			return -EINVAL;
 		dst = ebpf_to_mips_reg(ctx, insn, dst_reg);
 		if (dst < 0)
 			return dst;
-		if (insn->imm == 0) { /* Div by zero */
-			b_off = b_imm(exit_idx, ctx);
-			if (is_bad_offset(b_off))
-				return -E2BIG;
-			emit_instr(ctx, beq, MIPS_R_ZERO, MIPS_R_ZERO, b_off);
-			emit_instr(ctx, addu, MIPS_R_V0, MIPS_R_ZERO, MIPS_R_ZERO);
-		}
 		td = get_reg_val_type(ctx, this_idx, insn->dst_reg);
 		if (td == REG_64BIT || td == REG_32BIT_ZERO_EX)
 			/* sign extend */
@@ -770,19 +765,13 @@ static int build_one_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
 		break;
 	case BPF_ALU64 | BPF_DIV | BPF_K: /* ALU_IMM */
 	case BPF_ALU64 | BPF_MOD | BPF_K: /* ALU_IMM */
+		if (insn->imm == 0)
+			return -EINVAL;
 		dst = ebpf_to_mips_reg(ctx, insn, dst_reg);
 		if (dst < 0)
 			return dst;
-		if (insn->imm == 0) { /* Div by zero */
-			b_off = b_imm(exit_idx, ctx);
-			if (is_bad_offset(b_off))
-				return -E2BIG;
-			emit_instr(ctx, beq, MIPS_R_ZERO, MIPS_R_ZERO, b_off);
-			emit_instr(ctx, addu, MIPS_R_V0, MIPS_R_ZERO, MIPS_R_ZERO);
-		}
 		if (get_reg_val_type(ctx, this_idx, insn->dst_reg) == REG_32BIT)
 			emit_instr(ctx, dinsu, dst, MIPS_R_ZERO, 32, 32);
-
 		if (insn->imm == 1) {
 			/* div by 1 is a nop, mod by 1 is zero */
 			if (bpf_op == BPF_MOD)
-- 
2.9.5