linux-kernel - Re: [PATCH urgent v2] x86, asm: Disable opportunistic SYSRET if regs->flags has TF set

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Message-ID: <20150402160835.GC8045@gmail.com>
Date:	Thu, 2 Apr 2015 18:08:35 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Brian Gerst <brgerst@...il.com>, Andy Lutomirski <luto@...nel.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH urgent v2] x86, asm: Disable opportunistic SYSRET if
 regs->flags has TF set


* Denys Vlasenko <dvlasenk@...hat.com> wrote:

> On 04/02/2015 02:59 PM, Denys Vlasenko wrote:
> > On 04/02/2015 02:31 PM, Ingo Molnar wrote:
> >>   - we can optimize in a more directed fashion - like here
> >>
> >> ... while the downsides are:
> >>
> >>   - more code
> >>   - a (small) chance of a fix going to one path while not the other.
> >>
> >> How much extra code would it be?
> > 
> > A screenful or two.
> 
> I took a stab at it:
> 
>    text	   data	    bss	    dec	    hex	filename
>   12530	      0	      0	  12530	   30f2	entry_64.o2
>   12562	      0	      0	  12562	   3112	entry_64.o
> 
> The patch does two steps:
> 
> (1) copy-pastes "retint_swapgs:" code into syscall handling code,
> the copy is under "syscall_return:" label.
> 
> (2) remove "opportunistic sysret" code from "retint_swapgs" code block,
> since now it won't be reached by syscall return. This in fact removes
> most of the code in question.
> 
> Lightly run-tested so far.
> 
> Ingo, do you want this in a proper patch form?

Yeah, that looks good to me (only lightly reviewed).

Thanks,

	Ingo
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