linux-kernel - Re: [PATCH 2/2] alpha/ptrace: Add missing switch

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Message-ID: <YMpk7oNPSbVG0DSP@zeniv-ca.linux.org.uk>
Date:   Wed, 16 Jun 2021 20:54:06 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Michael Schmitz <schmitzmic@...il.com>,
        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 2/2] alpha/ptrace: Add missing switch_stack frames

On Wed, Jun 16, 2021 at 03:49:44PM -0500, Eric W. Biederman wrote:

> Someone might want or try to read them in the case of exit.  Which
> without some change will result in a read of other kernel stack content
> on alpha.

And someone might want a pony.  Again, why bother restoring those,
_especially_ in case of exit(2)?

> Plus there are coredumps which definitely want to read everything.

Huh?  In case of coredump we are going to have come through
$work_notifysig:
        mov     $sp, $16
	DO_SWITCH_STACK
	jsr     $26, do_work_pending
so they *do* have full pt_regs saved.  What's the problem?