Re: [PATCH v6 4/4] x86/ldt: Make modify_ldt optional

From: Ingo Molnar <mingo@kernel.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: X86 ML <x86@kernel.org>, Borislav Petkov <bp@alien8.de>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	"security@kernel.org" <security@kernel.org>,
	Sasha Levin <sasha.levin@oracle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Jan Beulich <jbeulich@suse.com>,
	xen-devel <xen-devel@lists.xen.org>
Subject: Re: [PATCH v6 4/4] x86/ldt: Make modify_ldt optional
Date: Fri, 31 Jul 2015 15:49:21 +0200	[thread overview]
Message-ID: <20150731134921.GA24245@gmail.com> (raw)
In-Reply-To: <a605166a771c343fd64802dece77a903507333bd.1438291540.git.luto@kernel.org>

* Andy Lutomirski <luto@kernel.org> wrote:

> The modify_ldt syscall exposes a large attack surface and is
> unnecessary for modern userspace.  Make it optional.
> 
> Reviewed-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
>  arch/x86/Kconfig                   | 17 +++++++++++++++++
>  arch/x86/include/asm/mmu.h         |  2 ++
>  arch/x86/include/asm/mmu_context.h | 28 +++++++++++++++++++++-------
>  arch/x86/kernel/Makefile           |  3 ++-
>  arch/x86/kernel/cpu/perf_event.c   |  4 ++++
>  arch/x86/kernel/process_64.c       |  2 ++
>  arch/x86/kernel/step.c             |  2 ++
>  kernel/sys_ni.c                    |  1 +
>  8 files changed, 51 insertions(+), 8 deletions(-)

btw., I fixed a (rare) build failure on MATH_EMULATION=y && !MODIFY_LDT_SYSCALL:

  arch/x86/math-emu/fpu_system.h:21:71: error: ‘mm_context_t’ has no member named ‘ldt’

I took the easy fix: made MATH_EMULATION depend on MODIFY_LDT_SYSCALL for now.

Thanks,

	Ingo