linux-kernel - Re: [PATCH 14/18] maccess: allow architectures to provide kernel probing directly

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Date:   Mon, 18 May 2020 17:09:03 +0200
From:   Christoph Hellwig <hch@....de>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Christoph Hellwig <hch@....de>, x86@...nel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-parisc@...r.kernel.org, linux-um@...ts.infradead.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 14/18] maccess: allow architectures to provide kernel
 probing directly

On Sat, May 16, 2020 at 12:42:59PM +0900, Masami Hiramatsu wrote:
> > Provide alternative versions of probe_kernel_read, probe_kernel_write
> > and strncpy_from_kernel_unsafe that don't need set_fs magic, but instead
> > use arch hooks that are modelled after unsafe_{get,put}_user to access
> > kernel memory in an exception safe way.
> 
> This patch seems to introduce new implementation of probe_kernel_read/write()
> and strncpy_from_kernel_unsafe(), but also drops copy_from/to_kernel_nofault()
> and strncpy_from_kernel_nofault() if HAVE_ARCH_PROBE_KERNEL is defined.
> In the result, this cause a link error with BPF and kprobe events.

That was just a bug as I didn't commit the changes to switch everything
to _nofault and remove _unsafe entirely, sorry.