From 68fda450a7df51cff9e5a4d4a4d9d0d5f2589153 Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Fri, 12 Jan 2018 18:59:52 -0800 Subject: [PATCH] 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: 622582786c9e ("net: filter: x86: internal BPF JIT") Fixes: 7a12b5031c6b ("sparc64: Add eBPF JIT.") Reported-by: syzbot+48340bb518e88849e2e3@syzkaller.appspotmail.com Signed-off-by: Alexei Starovoitov Signed-off-by: Daniel Borkmann --- kernel/bpf/verifier.c | 18 ++++++++++++++++++ net/core/filter.c | 4 ++++ 2 files changed, 22 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 20eb04fd155e..b7448347e6b6 100644 --- 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 index d339ef170df6..1c0eb436671f 100644 --- 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;