linux-kernel - Re: [PATCH 1/2] x86, mpx: explicitly disable 32-bit MPX support on 64-bit kernels

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Date:	Tue, 23 Dec 2014 10:19:44 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Dave Hansen <dave@...1.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>, X86 ML <x86@...nel.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH 1/2] x86, mpx: explicitly disable 32-bit MPX support on
 64-bit kernels


* Andy Lutomirski <luto@...capital.net> wrote:

> On Mon, Dec 22, 2014 at 12:21 PM, Dave Hansen <dave@...1.net> wrote:
> > On 12/22/2014 12:17 PM, Andy Lutomirski wrote:
> >>> >         /*
> >>> > +        * 32-bit binaries on 64-bit kernels are currently
> >>> > +        * unsupported.
> >>> > +        */
> >>> > +       if (IS_ENABLED(CONFIG_X86_64) && test_thread_flag(TIF_IA32))
> >>> > +               return MPX_INVALID_BOUNDS_DIR;
> >> Should this check mm->ia32_compat instead?
> >
> > set_personality_64bit/ia32() seem to make that and TIF_IA32 awfully
> > equivalent.  Is there a specific reason for wanting it done this way?
> 
> My general desire to remove various bogus TIF_IA32 references. 
> [...]

So we generally want to use mm->context.ia32_compat instead of 
TIF_IA32, because in the end TIF_IA32 will go away altogether?

Or do you just want to audit all TIF_IA32 places (because most of 
them are wrong), and using mm->context.ia32_compat where it's 
justified and eliminating TIF_IA32 use is a nice way to document 
that ongoing audit without breaking stuff and such?

> [...]  But this is only temporary, so I don't really care.

New code that touches this area should better use new principles, 
so I have no problem with requiring this, as long as it's well 
explained and logical and desirable to everyone.

Thanks,

	Ingo
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