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    Subject[PATCH 4.4 06/67] bpf: arsh is not supported in 32 bit alu thus reject it
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

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

    From: Daniel Borkmann <daniel@iogearbox.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@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>
    ---
    kernel/bpf/verifier.c | 5 +++++
    1 file changed, 5 insertions(+)

    --- a/kernel/bpf/verifier.c
    +++ b/kernel/bpf/verifier.c
    @@ -1165,6 +1165,11 @@ static int check_alu_op(struct verifier_
    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;

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