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Date:   Mon, 21 Jun 2021 02:27:52 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Michael Schmitz <schmitzmic@gmail.com>
Cc:     "Eric W. Biederman" <ebiederm@xmission.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Jens Axboe <axboe@kernel.dk>, Oleg Nesterov <oleg@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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        alpha <linux-alpha@vger.kernel.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        linux-m68k <linux-m68k@lists.linux-m68k.org>,
        Arnd Bergmann <arnd@kernel.org>,
        Ley Foon Tan <ley.foon.tan@intel.com>,
        Tejun Heo <tj@kernel.org>, Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH 1/2] alpha/ptrace: Record and handle the absence of
 switch_stack
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On Mon, Jun 21, 2021 at 02:01:18PM +1200, Michael Schmitz wrote:
> Hi Eric,
> 
> instrumenting get_reg on m68k and using a similar patch to yours to warn
> when unsaved registers are accessed on the switch stack, I get a hit from
> getegid and getegid32, just by running a simple ptrace on ls.
> 
> Going to wack those two moles now ...

Explain, please.  get_reg() is called by tracer; whose state are you checking?
Because you are *not* accessing the switch stack of the caller of get_reg().
And tracee should be in something like syscall_trace() or do_notify_resume();
both have SAVE_SWITCH_STACK done by the glue...