linux-kernel - Re: [PATCH] x86/ptrace: Remove questionable TS

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Message-ID: <20160620161409.GA29851@redhat.com>
Date:	Mon, 20 Jun 2016 18:14:10 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Pedro Alves <pedro@...ves.net>, Kees Cook <keescook@...omium.org>,
	Borislav Petkov <bp@...en8.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] x86/ptrace: Remove questionable TS_COMPAT usage in
	ptrace

On 06/20, Andy Lutomirski wrote:
>
> On Mon, Jun 20, 2016 at 8:24 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> >
> > How about the simple change below for now? IIRC 32-bit task can't use
> > "syscall" so if syscall_get_nr() >= 0 then even the wrong TS_COMPAT is
> > not that bad, even if it "leaks" to user-mode.
>
> Hmm.  That should fix the minor security issue, but it will even
> further break cross-arch tracing: now a 32-bit tracer tracing a 64-bit
> task that does int $0x80 will malfunction even more than it would
> have.

This is broken in any case. I mean, a 32-bit debugger can't really
debug a 64-bit task.

I don't think this change makes the things really worse.

> Also, it relies on bizarre arch details IMO.

Heh,  it looks as if your patch do not ;)

> I think I prefer my version, coming momentarily.

I disagree... I don't really understand why do we need the additional
complications for the minimal fix which doesn't look very nice anyway.

But I won't argue, and your patch looks correct to me.

Oleg.