bpf: fix 32-bit divide by zero

due to some JITs doing if (src_reg == 0) check in 64-bit mode for div/mod operations mask upper 32-bits of src register before doing the check Fixes: 6225827 ("net: filter: x86: internal BPF JIT") Fixes: 7a12b50 ("sparc64: Add eBPF JIT.") Reported-by: [email protected] Signed-off-by: Alexei Starovoitov <[email protected]> Signed-off-by: Daniel Borkmann <[email protected]>
siemens · Jan 14, 2018 · 68fda45 · 68fda45
1 parent c366287
commit 68fda45
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diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
@@ -4445,6 +4445,24 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env)
 	int i, cnt, delta = 0;
 
 	for (i = 0; i < insn_cnt; i++, insn++) {
+		if (insn->code == (BPF_ALU | BPF_MOD | BPF_X) ||
+		    insn->code == (BPF_ALU | BPF_DIV | BPF_X)) {
+			/* due to JIT bugs clear upper 32-bits of src register
+			 * before div/mod operation
+			 */
+			insn_buf[0] = BPF_MOV32_REG(insn->src_reg, insn->src_reg);
+			insn_buf[1] = *insn;
+			cnt = 2;
+			new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
+			if (!new_prog)
+				return -ENOMEM;
+
+			delta    += cnt - 1;
+			env->prog = prog = new_prog;
+			insn      = new_prog->insnsi + i + delta;
+			continue;
+		}
+
 		if (insn->code != (BPF_JMP | BPF_CALL))
 			continue;
 

diff --git a/net/core/filter.c b/net/core/filter.c
@@ -458,6 +458,10 @@ static int bpf_convert_filter(struct sock_filter *prog, int len,
 			    convert_bpf_extensions(fp, &insn))
 				break;
 
+			if (fp->code == (BPF_ALU | BPF_DIV | BPF_X) ||
+			    fp->code == (BPF_ALU | BPF_MOD | BPF_X))
+				*insn++ = BPF_MOV32_REG(BPF_REG_X, BPF_REG_X);
+
 			*insn = BPF_RAW_INSN(fp->code, BPF_REG_A, BPF_REG_X, 0, fp->k);
 			break;