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bpf: fix 32-bit divide by zero

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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: 622582786c ("net: filter: x86: internal BPF JIT")
Fixes: 7a12b5031c ("sparc64: Add eBPF JIT.")
Reported-by: syzbot+48340bb518e88849e2e3@syzkaller.appspotmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Alexei Starovoitov 2018-01-12 18:59:52 -08:00 committed by Daniel Borkmann
parent c366287ebd
commit 68fda450a7
2 changed files with 22 additions and 0 deletions
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18
kernel/bpf/verifier.c
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@ -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;

4
net/core/filter.c
View File

@ -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;