linux-kernel - Re: [PATCH 1/2] alpha/ptrace: Record and handle the absence of switch

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Date:   Mon, 21 Jun 2021 02:27:52 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Michael Schmitz <schmitzmic@...il.com>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>, Oleg Nesterov <oleg@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        alpha <linux-alpha@...r.kernel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Arnd Bergmann <arnd@...nel.org>,
        Ley Foon Tan <ley.foon.tan@...el.com>,
        Tejun Heo <tj@...nel.org>, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH 1/2] alpha/ptrace: Record and handle the absence of
 switch_stack

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...