linux-kernel - Re: [RFC v2] x86-64: Allow emulated vsyscalls from user addresses

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Message-ID: <CAObL_7EWkNhWDW6oMsAk6fa0Drhf=zQhJ1+sFmynk=ohq+RevQ@mail.gmail.com>
Date:	Sun, 7 Aug 2011 12:14:46 -0400
From:	Andrew Lutomirski <luto@....edu>
To:	Borislav Petkov <bp@...en8.de>, Andrew Lutomirski <luto@....edu>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Andi Kleen <andi@...stfloor.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	lueckintel@...oo.com, kimwooyoung@...il.com,
	Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: [RFC v2] x86-64: Allow emulated vsyscalls from user addresses

On Sun, Aug 7, 2011 at 11:44 AM, Borislav Petkov <bp@...en8.de> wrote:
> On Sun, Aug 07, 2011 at 08:58:56AM -0400, Andrew Lutomirski wrote:
>> > Also, what do we do with userspace which decides to hardcode "int 0x4[012]"
>> > somewhere in the meantime?
>>
>> Break it?  Any code that does that will get an unconditional warning
>> with this patch.
>
> Ok, I hope you're right. Because I'm sure you remember the last
> prominent time the kernel broke userspace in the face of powertop.
> Although having the warning should be fine, i.e. along the lines of "you
> silly userspace process have been warned."

We have an advantage this time: why would anyone want to use them?
They're annoying to use and they're slower than syscalls.

We could resurrect the patch that randomized the vectors at boot, but
that was IMO ugly.

--Andy
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