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 <20220121174145.3433628-1-kennyyu@fb.com>
In-Reply-To: <20220121174145.3433628-1-kennyyu@fb.com>
From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Fri, 21 Jan 2022 09:47:13 -0800
Message-ID: <CAADnVQKZa_rm3sybP=Rt4Nm-zYrv4s9XvF7PGDFTOBD-TDu23g@mail.gmail.com>
Subject: Re: [PATCH v5 bpf-next 1/3] bpf: Add bpf_access_process_vm() helper
To:     Kenny Yu <kennyyu@fb.com>
Cc:     Andrii Nakryiko <andrii.nakryiko@gmail.com>,
        Andrii Nakryiko <andrii@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>, bpf <bpf@vger.kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Gabriele <phoenix1987@gmail.com>, Yonghong Song <yhs@fb.com>
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On Fri, Jan 21, 2022 at 9:42 AM Kenny Yu <kennyyu@fb.com> wrote:
>
> Thanks for the suggestions! I'll go with the all-or-nothing approach to
> be consistent with `bpf_copy_from_user` and will make the following changes:
>
> * Return value: returns 0 on success, or negative error on failure.
> * If we had a partial read, we will memset the read bytes to 0 and return
>   -EFAULT

Not read bytes, but all bytes.
copy_from_user zeros leftover for us, but access_process_vm doesn't
do this on partial read.