From: Dave Hansen <dave@sr71.net>
To: Andy Lutomirski <luto@amacapital.net>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>, X86 ML <x86@kernel.org>
Subject: Re: [RFC][PATCH 0/8] x86, mpx: Support 32-bit binaries on 64-bit kernels
Date: Fri, 12 Dec 2014 13:41:08 -0800 [thread overview]
Message-ID: <548B60F4.6020903@sr71.net> (raw)
In-Reply-To: <CALCETrW4f3EUYGG_zyzb7sZBXaoW3eHMpTn3dd3WpDgJq2HjtA@mail.gmail.com>
On 12/12/2014 12:48 PM, Andy Lutomirski wrote:
> On Fri, Dec 12, 2014 at 12:27 PM, Dave Hansen <dave@sr71.net> wrote:
>> You want the same size structures with the same format for 32-bit and
>> 64-bit modes?
>
> Yes. Especially because programs can switch between 32-bit and 64-bit
> mode entirely in userspace. I don't know whether any do in practice,
> but programs *can*.
So, you want a 2GB of the 32-bit address space dedicated to a bounds
directory, and half of the space for the bounds tables to be simply
zero-filled unused address bits? That seems, um, a bit unreasonable.
> Or better yet: Intel could have skipped supporting it at all in 32-bit
> mode.
So, we should not have this security feature for 32-bit apps... because
it costs us 50 lines of code in the kernel to support? Did you look at
the diffstat?
> Isn't mpx somewhat of an address space hog anyway?
Yes, it will be troublesome for 32-bit apps that are already bumping up
against the virtual address space size to support it. But, really, how
many of those *are* there these days?
next prev parent reply other threads:[~2014-12-12 21:41 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-12 19:12 [RFC][PATCH 0/8] x86, mpx: Support 32-bit binaries on 64-bit kernels Dave Hansen
2014-12-12 19:12 ` [RFC][PATCH 1/8] x86: make is_64bit_mm() widely available Dave Hansen
2014-12-12 19:12 ` [RFC][PATCH 2/8] x86: make __VIRTUAL_MASK safe to use on 32 bit Dave Hansen
2014-12-12 19:12 ` [RFC][PATCH 3/8] x86, mpx: we do not allocate the bounds directory Dave Hansen
2014-12-12 19:12 ` [RFC][PATCH 4/8] x86, mpx: remove redundant MPX_BNDCFG_ADDR_MASK Dave Hansen
2014-12-12 19:12 ` [RFC][PATCH 5/8] x86, mpx: Add temporary variable to reduce masking Dave Hansen
2014-12-12 19:12 ` [RFC][PATCH 6/8] x86, mpx: new directory entry to addr helper Dave Hansen
2014-12-12 19:12 ` [RFC][PATCH 7/8] x86, mpx: do 32-bit-only cmpxchg for 32-bit apps Dave Hansen
2014-12-12 19:12 ` [RFC][PATCH 8/8] x86, mpx: support 32bit binaries on 64bit kernel Dave Hansen
2014-12-12 20:22 ` [RFC][PATCH 0/8] x86, mpx: Support 32-bit binaries on 64-bit kernels Andy Lutomirski
2014-12-12 20:27 ` Dave Hansen
2014-12-12 20:48 ` Andy Lutomirski
2014-12-12 21:41 ` Dave Hansen [this message]
2014-12-12 23:04 ` Andy Lutomirski
2014-12-12 23:16 ` Dave Hansen
2014-12-13 0:11 ` Andy Lutomirski
2014-12-13 0:23 ` Dave Hansen
2014-12-13 1:45 ` Andy Lutomirski
2014-12-13 15:50 ` Dave Hansen
2014-12-12 20:27 ` Andy Lutomirski
2014-12-12 20:35 ` Dave Hansen
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