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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 13 May 2020 16:59:40 -0700
Message-ID: <CAHk-=wjBKGLyf1d53GwfUTZiK_XPdujwh+u2XSpD2HWRV01Afw@mail.gmail.com>
Subject: Re: [PATCH 11/18] maccess: remove strncpy_from_unsafe
To:     Masami Hiramatsu <mhiramat@kernel.org>
Cc:     Daniel Borkmann <daniel@iogearbox.net>,
        Christoph Hellwig <hch@lst.de>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-parisc@vger.kernel.org,
        linux-um <linux-um@lists.infradead.org>,
        Netdev <netdev@vger.kernel.org>, bpf@vger.kernel.org,
        Linux-MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Wed, May 13, 2020 at 4:21 PM Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
>
> For trace_kprobe.c current order (kernel -> user fallback) is preferred
> because it has another function dedicated for user memory.

Well, then it should just use the "strict" kernel-only one for the
non-user memory.

But yes, if there are legacy interfaces, then we might want to say
"these continue to work for the legacy case on platforms where we can
tell which kind of pointer it is from the bit pattern".

But we should likely at least disallow it entirely on platforms where
we really can't - or pick one hardcoded choice. On sparc, you really
_have_ to specify one or the other.

                  Linus