Commit fcabc6d0 authored Jan 29, 2018 by Daniel Borkmann Committed by Greg Kroah-Hartman Jan 31, 2018

bpf: arsh is not supported in 32 bit alu thus reject it



[ upstream commit 7891a87efc7116590eaba57acc3c422487802c6f ]

The following snippet was throwing an 'unknown opcode cc' warning
in BPF interpreter:

  0: (18) r0 = 0x0
  2: (7b) *(u64 *)(r10 -16) = r0
  3: (cc) (u32) r0 s>>= (u32) r0
  4: (95) exit

Although a number of JITs do support BPF_ALU | BPF_ARSH | BPF_{K,X}
generation, not all of them do and interpreter does neither. We can
leave existing ones and implement it later in bpf-next for the
remaining ones, but reject this properly in verifier for the time
being.

Fixes: 17a52670 ("bpf: verifier (add verifier core)")
Reported-by:  <syzbot+93c4904c5c70348a6890@syzkaller.appspotmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent a3d6dd6a

kernel/bpf/verifier.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -1843,6 +1843,11 @@ static int check_alu_op(struct bpf_verifier_env env, struct bpf_insn insn)
		return -EINVAL;
		}

		if (opcode == BPF_ARSH && BPF_CLASS(insn->code) != BPF_ALU64) {
		verbose("BPF_ARSH not supported for 32 bit ALU\n");
		return -EINVAL;
		}

		if ((opcode == BPF_LSH \|\| opcode == BPF_RSH \|\|
		opcode == BPF_ARSH) && BPF_SRC(insn->code) == BPF_K) {
		int size = BPF_CLASS(insn->code) == BPF_ALU64 ? 64 : 32;