netdev - Re: [PATCH net-next] bpf: Preserve const register type on const OR alu ops

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Message-ID: <58435847.2000406@iogearbox.net>
Date:   Sun, 04 Dec 2016 00:41:59 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Alexei Starovoitov <ast@...com>,
        "David S . Miller" <davem@...emloft.net>
CC:     Gianluca Borello <g.borello@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] bpf: Preserve const register type on const OR
 alu ops

On 12/03/2016 09:31 PM, Alexei Starovoitov wrote:
> From: Gianluca Borello <g.borello@...il.com>
>
> Occasionally, clang (e.g. version 3.8.1) translates a sum between two
> constant operands using a BPF_OR instead of a BPF_ADD. The verifier is
> currently not handling this scenario, and the destination register type
> becomes UNKNOWN_VALUE even if it's still storing a constant. As a result,
> the destination register cannot be used as argument to a helper function
> expecting a ARG_CONST_STACK_*, limiting some use cases.
>
> Modify the verifier to handle this case, and add a few tests to make sure
> all combinations are supported, and stack boundaries are still verified
> even with BPF_OR.
>
> Signed-off-by: Gianluca Borello <g.borello@...il.com>
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>

Acked-by: Daniel Borkmann <daniel@...earbox.net>