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

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Message-ID: <20160619211906.GA14712@redhat.com>
Date:	Sun, 19 Jun 2016 23:19:07 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	x86@...nel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Kees Cook <keescook@...omium.org>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH] x86/ptrace: Remove questionable TS_COMPAT usage in
	ptrace

Let me first thank Pedro who has already replied!

And I have to admit I will need to re-read his explanations after
sleep to (try to) convince myself I fully understans the problems ;)
Too late for me.

Right now I have nothing to add, but

On 06/18, Andy Lutomirski wrote:
>
> @@ -922,16 +922,7 @@ static int putreg32(struct task_struct *child, unsigned regno, u32 value)
>  	R32(esp, sp);
>  
>  	case offsetof(struct user32, regs.orig_eax):
> -		/*
> -		 * A 32-bit debugger setting orig_eax means to restore
> -		 * the state of the task restarting a 32-bit syscall.
> -		 * Make sure we interpret the -ERESTART* codes correctly
> -		 * in case the task is not actually still sitting at the
> -		 * exit from a 32-bit syscall with TS_COMPAT still set.
> -		 */
>  		regs->orig_ax = value;
> -		if (syscall_get_nr(child, regs) >= 0)
> -			task_thread_info(child)->status |= TS_COMPAT;

I agree it would be nice to remove this code, but then it is not clear
how/when we should sign-extend regs->ax..

And this leads to another question, why do we actually need to set/clear
TS_COMPAT in set_personality_ia32() ??

Oleg.