netdev - Re: [PATCH 11/18] maccess: remove strncpy_from

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Date:   Thu, 14 May 2020 10:00:09 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Christoph Hellwig <hch@....de>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-parisc@...r.kernel.org,
        linux-um <linux-um@...ts.infradead.org>,
        Netdev <netdev@...r.kernel.org>, bpf@...r.kernel.org,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 11/18] maccess: remove strncpy_from_unsafe

On Wed, 13 May 2020 16:59:40 -0700
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Wed, May 13, 2020 at 4:21 PM Masami Hiramatsu <mhiramat@...nel.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".

Yes, that was why I changed my mind and send reviewed-by last time.

https://lore.kernel.org/bpf/20200511142716.f1ff6fc55220012982c47fec@kernel.org/

> 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.

OK. BTW, is there any way to detect the kernel/user space overlap on
memory layout statically? If there, I can do it. (I don't like
"if (CONFIG_X86)" thing....)
Or, maybe we need CONFIG_ARCH_OVERLAP_ADDRESS_SPACE?

Thank you,

-- 
Masami Hiramatsu <mhiramat@...nel.org>