linux-kernel - [PATCH 4.9 62/66] bpf: arsh is not supported in 32 bit alu thus reject it

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Message-Id: <20180129123843.167617307@linuxfoundation.org>
Date:   Mon, 29 Jan 2018 13:57:26 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "ast@...nel.org, stable@...r.kernel.org, Daniel Borkmann" 
        <daniel@...earbox.net>,
        syzbot+93c4904c5c70348a6890@...kaller.appspotmail.com,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: [PATCH 4.9 62/66] bpf: arsh is not supported in 32 bit alu thus reject it

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Daniel Borkmann <daniel@...earbox.net>

[ 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: 17a5267067f3 ("bpf: verifier (add verifier core)")
Reported-by: syzbot+93c4904c5c70348a6890@...kaller.appspotmail.com
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 kernel/bpf/verifier.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1843,6 +1843,11 @@ static int check_alu_op(struct bpf_verif
 			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;