netdev - Bug with BPF_ALU64

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Message-ID: <52c7df55-84d9-f6d2-ed84-51ac90eb6bcc@solarflare.com>
Date:   Thu, 14 Sep 2017 18:53:17 +0100
From:   Edward Cree <ecree@...arflare.com>
To:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...com>
CC:     netdev <netdev@...r.kernel.org>
Subject: Bug with BPF_ALU64 | BPF_END?

Is BPF_END supposed to only be used with BPF_ALU, never with BPF_ALU64?
In kernel/bpf/core.c:___bpf_prog_run(), there are only jump table targets
 for the BPF_ALU case, not for the BPF_ALU64 case (opcodes 0xd7 and 0xdf).
But the verifier doesn't enforce this; by crafting a program that uses
 these opcodes I can get a WARN when they're run (without JIT; it looks
 like the x86 JIT, at least, won't like it either).
Proposed patch below the cut; build-tested only.

-Ed
---

[PATCH net] bpf/verifier: reject BPF_ALU64|BPF_END

Neither ___bpf_prog_run nor the JITs accept it.

Fixes: 17a5267067f3 ("bpf: verifier (add verifier core)")
Signed-off-by: Edward Cree <ecree@...arflare.com>
---
 kernel/bpf/verifier.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 477b693..799b245 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2292,7 +2292,8 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
 			}
 		} else {
 			if (insn->src_reg != BPF_REG_0 || insn->off != 0 ||
-			    (insn->imm != 16 && insn->imm != 32 && insn->imm != 64)) {
+			    (insn->imm != 16 && insn->imm != 32 && insn->imm != 64) ||
+			    BPF_CLASS(insn->code) == BPF_ALU64) {
 				verbose("BPF_END uses reserved fields\n");
 				return -EINVAL;
 			}