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Date:   Fri, 22 May 2020 09:22:11 +0900
From:   Masami Hiramatsu <>
To:     Christoph Hellwig <>
Cc:, Alexei Starovoitov <>,
        Daniel Borkmann <>,
        Linus Torvalds <>,
        Andrew Morton <>,,,,,,
Subject: Re: clean up and streamline probe_kernel_* and friends v4

On Thu, 21 May 2020 17:22:38 +0200
Christoph Hellwig <> wrote:

> Hi all,
> this series start cleaning up the safe kernel and user memory probing
> helpers in mm/maccess.c, and then allows architectures to implement
> the kernel probing without overriding the address space limit and
> temporarily allowing access to user memory.  It then switches x86
> over to this new mechanism by reusing the unsafe_* uaccess logic.
> This version also switches to the saner copy_{from,to}_kernel_nofault
> naming suggested by Linus.
> I kept the x86 helpers as-is without calling unsage_{get,put}_user as
> that avoids a number of hard to trace casts, and it will still work
> with the asm-goto based version easily.
> Changes since v3:
>  - cleanup how bpf and trace_kprobe perform the TASK_SIZE checks
>  - remove the unused dst argument to probe_kernel_read_allowed
>  - document the -ERANGE return value

This series looks good to me.

Reviewed-by: Masami Hiramatsu <>

for this series.

Thank you!

> Changes since v2:
>  - rebased on 5.7-rc6 with the bpf trace format string changes
>  - rename arch_kernel_read to __get_kernel_nofault and arch_kernel_write
>    to __put_kernel_nofault
>  - clean up the tracers to only allowd "mixed" reads when the kernel
>    has non-overlapping address spaces

Masami Hiramatsu <>

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