Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Fri, 29 Nov 2019 18:32:13 +0100
From:   Oleg Nesterov <oleg@redhat.com>
To:     Andy Lutomirski <luto@amacapital.net>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Borislav Petkov <bp@alien8.de>, Ingo Molnar <mingo@kernel.org>,
        Jan Kratochvil <jan.kratochvil@redhat.com>,
        Pedro Alves <palves@redhat.com>, Peter Anvin <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        the arch/x86 maintainers <x86@kernel.org>
Subject: Re: [PATCH] ptrace/x86: introduce TS_COMPAT_RESTART to fix
 get_nr_restart_syscall()
Message-ID: <20191129173213.GB3992@redhat.com>
References: <CAHk-=whA1h-7MKGdzyViwJR4_rqYKMP91FwuObWneBZE0yH81A@mail.gmail.com>
 <EB7AF2AE-6CA3-4395-AA37-BF92EE308A42@amacapital.net>
MIME-Version: 1.0
In-Reply-To: <EB7AF2AE-6CA3-4395-AA37-BF92EE308A42@amacapital.net>
User-Agent: Mutt/1.5.24 (2015-08-30)
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable
Content-Disposition: inline
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 11/28, Andy Lutomirski wrote:
>
> I think this doesn=E2=80=99t work for x32.

Why? get_nr_restart_syscall() can still rely on the "orig_ax & __X32_SYSCAL=
L_BIT"
check, debugger should restore regs->orig_ax correctly.

> Let=E2=80=99s either save the result of syscall_get_arch()

We can save the result of syscall_get_arch(), but it doesn't distinguish
x32/x86_64 tasks, so it doesn't really differ from TS_COMPAT.

> or just actually calculate and save the restart_syscall nr here.

sure, we we can do this.

> Before we commit to this, Kees, do you think we can manage to just renumb=
er
> restart_syscall()?  That=E2=80=99s a much better solution if we can pull =
it off.

Agreed.

Oleg.