netdev - Re: [bpf PATCH] bpf: Do not allow btf_ctx_access with _

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Message-ID: <d53db444-8473-a48c-179f-4baf13a97674@iogearbox.net>
Date:   Thu, 25 Jun 2020 17:01:40 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     John Fastabend <john.fastabend@...il.com>, jolsa@...nel.org,
        andrii.nakryiko@...il.com, ast@...nel.org
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [bpf PATCH] bpf: Do not allow btf_ctx_access with __int128 types

On 6/25/20 12:20 AM, John Fastabend wrote:
> To ensure btf_ctx_access() is safe the verifier checks that the BTF
> arg type is an int, enum, or pointer. When the function does the
> BTF arg lookup it uses the calculation 'arg = off / 8'  using the
> fact that registers are 8B. This requires that the first arg is
> in the first reg, the second in the second, and so on. However,
> for __int128 the arg will consume two registers by default LLVM
> implementation. So this will cause the arg layout assumed by the
> 'arg = off / 8' calculation to be incorrect.
> 
> Because __int128 is uncommon this patch applies the easiest fix and
> will force int types to be sizeof(u64) or smaller so that they will
> fit in a single register.
> 
> v2: remove unneeded parens per Andrii's feedback
> 
> Fixes: 9e15db66136a1 ("bpf: Implement accurate raw_tp context access via BTF")
> Acked-by: Andrii Nakryiko <andriin@...com>
> Signed-off-by: John Fastabend <john.fastabend@...il.com>

Applied, thanks!