[PATCH 6/6] ebpf: allow BPF_REG_X in src_reg conditional jumps

Tycho Andersen
2015-09-04T16:06:01Z

The classic converter generates conditional jumps with:

if (BPF_SRC(fp->code) == BPF_K && (int) fp->k < 0) {
...
} else {
insn->dst_reg = BPF_REG_A;
insn->src_reg = BPF_REG_X;
insn->imm = fp->k;
bpf_src = BPF_SRC(fp->code);
}

but here, we enforce that the src_reg == BPF_REG_0. We should also allow
BPF_REG_X since that's what the converter generates; this enables us to
load eBPF programs that were generated by the converter.

Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
CC: Kees Cook <keescook@chromium.org>
CC: Will Drewry <wad@chromium.org>
CC: Oleg Nesterov <oleg@redhat.com>
CC: Andy Lutomirski <luto@amacapital.net>
CC: Pavel Emelyanov <xemul@parallels.com>
CC: Serge E. Hallyn <serge.hallyn@ubuntu.com>
CC: Alexei Starovoitov <ast@kernel.org>
CC: Daniel Borkmann <daniel@iogearbox.net>
---
kernel/bpf/verifier.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 039d866..2fff8cd 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1080,7 +1080,12 @@ static int check_cond_jmp_op(struct verifier_env *env,
if (err)
return err;
} else {
- if (insn->src_reg != BPF_REG_0) {
+ switch (insn->src_reg) {
+ case BPF_REG_0:
+ /* the classic converter generates BPF_JMP with src_reg of X */
+ case BPF_REG_X:
+ break;
+ default:
verbose("BPF_JMP uses reserved fields\n");
return -EINVAL;
}
--
2.1.4