Re: [PATCH] x86/asm/entry: Remove user_mode_ignore_vm86()

From: Borislav Petkov <bp@alien8.de>
To: Ingo Molnar <mingo@kernel.org>
Cc: Denys Vlasenko <dvlasenk@redhat.com>,
	Andy Lutomirski <luto@amacapital.net>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Brad Spengler <spender@grsecurity.net>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andrew Lutomirski <luto@kernel.org>,
	"linux-tip-commits@vger.kernel.org" 
	<linux-tip-commits@vger.kernel.org>
Subject: Re: [PATCH] x86/asm/entry: Remove user_mode_ignore_vm86()
Date: Sun, 29 Mar 2015 14:13:47 +0200	[thread overview]
Message-ID: <20150329121347.GC4973@pd.tnic> (raw)
In-Reply-To: <20150329090233.GA1963@gmail.com>

On Sun, Mar 29, 2015 at 11:02:34AM +0200, Ingo Molnar wrote:
> So how about doing the patch below?
> 
> Thanks,
> 
> 	Ingo
> 
> ===================================>
> From 6677d6f073cfda7f1036eb06d13faaad5c6742cc Mon Sep 17 00:00:00 2001
> From: Ingo Molnar <mingo@kernel.org>
> Date: Sun, 29 Mar 2015 09:10:08 +0200
> Subject: [PATCH] x86/asm/entry: Remove user_mode_ignore_vm86()
> 
> user_mode_ignore_vm86() can be used instead of user_mode(), in
> places where we have already done a v8086_mode() security
> check of ptregs.
> 
> But doing this check in the wrong place would be a bug that could
> result in security problems, and also the naming still isn't very clear.
> 
> Furthermore, it only affects 32-bit kernels, while most development
> happens on 64-bit kernels.
> 
> If we replace them with user_mode() checks then the cost is only a
> very minor increase in various slowpaths:
> 
>    text             data   bss     dec              hex    filename
>    10573391         703562 1753042 13029995         c6d26b vmlinux.o.before
>    10573423         703562 1753042 13030027         c6d28b vmlinux.o.after
> 
> So lets get rid of this distinction once and for all.
> 
> Cc: Andy Lutomirski <luto@amacapital.net>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Denys Vlasenko <dvlasenk@redhat.com>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
> ---
>  arch/x86/include/asm/ptrace.h    | 17 -----------------
>  arch/x86/kernel/cpu/perf_event.c |  2 +-
>  arch/x86/kernel/traps.c          |  6 +++---
>  3 files changed, 4 insertions(+), 21 deletions(-)

I had some doubts about people using user_mode_ignore_vm86() in the
wrong way and thus introducing sec. bugs.

Since this is only on the slow path, simplifying the code makes sense to
me.

Acked-by: Borislav Petkov <bp@suse.de>

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--