linux-kernel - Re: [PATCH 00/11] x86: Supervisor Mode Access Prevention

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Message-ID: <505CD854.1030502@zytor.com>
Date:	Fri, 21 Sep 2012 14:12:52 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Kees Cook <keescook@...omium.org>,
	Linda Wang <lwang@...hat.com>,
	Matt Fleming <matt.fleming@...el.com>
Subject: Re: [PATCH 00/11] x86: Supervisor Mode Access Prevention

On 09/21/2012 02:09 PM, Linus Torvalds wrote:
> On Fri, Sep 21, 2012 at 2:03 PM, H. Peter Anvin <hpa@...ux.intel.com> wrote:
>>
>> A while ago I also did a mockup patch which switched %cr3 to
>> swapper_pg_dir while entering the kernel (basically where the CLAC
>> instructions go, plus the SYSCALL path; a restore was obviously needed,
>> too.)  The performance was atrocious, but I didn't remember running into
>> any problems.
> 
> Well, they are bound to be corner-cases and unusual. I was thinking of
> problems like the one recently fixed in commit ed6fe9d614fc ("Fix
> order of arguments to compat_put_time[spec|val]"), which really
> requires compat handling of fairly unusual cases.
> 
> That's the kind of situation where I'd expect bugs might still lurk.
> And it would only get triggered by some rather unusual setups.
> 

Yes; in *most* cases these are exploitable security bugs on non-SMAP
hardware (which is obviously the whole point!), but there are a few
conditions where there may be issues that aren't exploitable problems.

	-hpa



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