linux-kernel - Re: [PATCH 1/5] x86/vm86: Move userspace accesses to do_sys

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Message-ID: <CALCETrU+=-bwux-FRSAy2YhEsTV8V1=vtiW5SbShQH+VhobC2A@mail.gmail.com>
Date:	Sat, 11 Jul 2015 09:37:35 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Brian Gerst <brgerst@...il.com>
Cc:	X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/5] x86/vm86: Move userspace accesses to do_sys_vm86()

On Fri, Jul 10, 2015 at 10:09 PM, Brian Gerst <brgerst@...il.com> wrote:
> Move the userspace accesses down into the common function in
> preparation for the next set of patches.
>

One thing I don't like about the current code that makes these patches
harder to review is the bizarre approach to copying.  If you changed
this:

> -       tmp = copy_vm86_regs_from_user(&info.regs, &v86->regs,
> -                                      offsetof(struct kernel_vm86_struct, vm86plus) -
> -                                      sizeof(info.regs));

into a normal field-by-field get_user / copy_from_user (the latter for
the big regs struct) then it would be clear what the ABI is and it
would be much easier to read the patches and confirm that you aren't
accidentally changing the ABI.

You could also get rid of the constraint that certain fields in
apparently kernel-internal structs had to be in a certain order.

Other than that, patches 1-4 look good on cursory inspection.  I'll
look more carefully later.  I need to think about patch 5 more.

--Andy
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