linux-kernel - Re: PTRACE_SYSEMU behavior difference on arm64

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Message-ID: <CABV8kRxD3_zh_WJy0jWVpxxNG_NSwoTJXdLd8Ym9Bm7PbHhftQ@mail.gmail.com>
Date:   Fri, 15 May 2020 16:43:58 -0400
From:   Keno Fischer <keno@...iacomputing.com>
To:     Will Deacon <will@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: PTRACE_SYSEMU behavior difference on arm64

On Fri, May 15, 2020 at 8:13 AM Will Deacon <will@...nel.org> wrote:
> But it also
> means that nobody is using this on arm64, so we could also consider removing
> it entirely. Did you spot this because you are trying to use it for
> something or just by inspection/unit-testing?

No, I was trying to port a tool from x86 and nothing made sense for
many hours :). (it was quite a bit of debugging, because the
syscall that it was supposed to skip installed a seccomp filter,
which then later veto'd random syscalls making the
symptoms quite confusing). Having PTRACE_SYSEMU isn't
critical, but we might as well support it.
It makes things a bit more efficient and is probably safer
(if it works correctly ;). The patch is fairly small. Will validate
and then send it here for review.

Keno