linux-kernel - Re: [PATCH] [RFC] x86: work around MPX Erratum

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Message-ID: <CALCETrWaW21JEkD3m-smvetJdSqwb5rfyWao4paNbKPi4oVU+Q@mail.gmail.com>
Date:	Tue, 3 May 2016 14:44:08 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Dave Hansen <dave.hansen@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>
Subject: Re: [PATCH] [RFC] x86: work around MPX Erratum

On Tue, May 3, 2016 at 2:39 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Tue, May 3, 2016 at 2:31 PM, Andy Lutomirski <luto@...capital.net> wrote:
>>
>> Having actually read the erratum: how can this affect Linux at all
>> under any scenario where user code hasn't already completely
>> compromised the kernel?
>
> If it matches purely on linear address, you will potentially have
> interesting situations with people running in virtualized environments
> and crashing programs in other virtual containers or the host.

If so, how does SMEP help?  There's no guarantee that the same linear
address in two different VMs has the same U/S bit in the page tables.

IOW, I'm having trouble seeing a situation under which SMEP matters
and Linux would be affected in the absence of SMEP.

--Andy